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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
0d4e6ca3 | 3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 2009, 2010 |
07d83abe MV |
4 | @c Free Software Foundation, Inc. |
5 | @c See the file guile.texi for copying conditions. | |
6 | ||
07d83abe MV |
7 | @node Scheduling |
8 | @section Threads, Mutexes, Asyncs and Dynamic Roots | |
9 | ||
07d83abe MV |
10 | @menu |
11 | * Arbiters:: Synchronization primitives. | |
12 | * Asyncs:: Asynchronous procedure invocation. | |
07d83abe | 13 | * Threads:: Multiple threads of execution. |
2567692a | 14 | * Mutexes and Condition Variables:: Synchronization primitives. |
b4fddbbe | 15 | * Blocking:: How to block properly in guile mode. |
2567692a | 16 | * Critical Sections:: Avoiding concurrency and reentries. |
b4fddbbe | 17 | * Fluids and Dynamic States:: Thread-local variables, etc. |
0d4e6ca3 | 18 | * Futures:: Fine-grain parallelism. |
07d83abe MV |
19 | * Parallel Forms:: Parallel execution of forms. |
20 | @end menu | |
21 | ||
22 | ||
23 | @node Arbiters | |
24 | @subsection Arbiters | |
07d83abe MV |
25 | @cindex arbiters |
26 | ||
e136aab0 KR |
27 | Arbiters are synchronization objects, they can be used by threads to |
28 | control access to a shared resource. An arbiter can be locked to | |
29 | indicate a resource is in use, and unlocked when done. | |
07d83abe | 30 | |
b4fddbbe MV |
31 | An arbiter is like a light-weight mutex (@pxref{Mutexes and Condition |
32 | Variables}). It uses less memory and may be faster, but there's no | |
33 | way for a thread to block waiting on an arbiter, it can only test and | |
34 | get the status returned. | |
07d83abe MV |
35 | |
36 | @deffn {Scheme Procedure} make-arbiter name | |
37 | @deffnx {C Function} scm_make_arbiter (name) | |
cdf1ad3b MV |
38 | Return an object of type arbiter and name @var{name}. Its |
39 | state is initially unlocked. Arbiters are a way to achieve | |
40 | process synchronization. | |
07d83abe MV |
41 | @end deffn |
42 | ||
43 | @deffn {Scheme Procedure} try-arbiter arb | |
44 | @deffnx {C Function} scm_try_arbiter (arb) | |
cdf1ad3b MV |
45 | If @var{arb} is unlocked, then lock it and return @code{#t}. |
46 | If @var{arb} is already locked, then do nothing and return | |
47 | @code{#f}. | |
07d83abe MV |
48 | @end deffn |
49 | ||
50 | @deffn {Scheme Procedure} release-arbiter arb | |
51 | @deffnx {C Function} scm_release_arbiter (arb) | |
e136aab0 KR |
52 | If @var{arb} is locked, then unlock it and return @code{#t}. If |
53 | @var{arb} is already unlocked, then do nothing and return @code{#f}. | |
54 | ||
55 | Typical usage is for the thread which locked an arbiter to later | |
56 | release it, but that's not required, any thread can release it. | |
07d83abe MV |
57 | @end deffn |
58 | ||
59 | ||
60 | @node Asyncs | |
61 | @subsection Asyncs | |
62 | ||
63 | @cindex asyncs | |
64 | @cindex user asyncs | |
65 | @cindex system asyncs | |
66 | ||
1021bb7a | 67 | Asyncs are a means of deferring the execution of Scheme code until it is |
07d83abe MV |
68 | safe to do so. |
69 | ||
70 | Guile provides two kinds of asyncs that share the basic concept but are | |
71 | otherwise quite different: system asyncs and user asyncs. System asyncs | |
72 | are integrated into the core of Guile and are executed automatically | |
73 | when the system is in a state to allow the execution of Scheme code. | |
74 | For example, it is not possible to execute Scheme code in a POSIX signal | |
75 | handler, but such a signal handler can queue a system async to be | |
76 | executed in the near future, when it is safe to do so. | |
77 | ||
78 | System asyncs can also be queued for threads other than the current one. | |
79 | This way, you can cause threads to asynchronously execute arbitrary | |
80 | code. | |
81 | ||
82 | User asyncs offer a convenient means of queueing procedures for future | |
83 | execution and triggering this execution. They will not be executed | |
84 | automatically. | |
85 | ||
86 | @menu | |
74926120 NJ |
87 | * System asyncs:: |
88 | * User asyncs:: | |
07d83abe MV |
89 | @end menu |
90 | ||
91 | @node System asyncs | |
92 | @subsubsection System asyncs | |
93 | ||
94 | To cause the future asynchronous execution of a procedure in a given | |
95 | thread, use @code{system-async-mark}. | |
96 | ||
97 | Automatic invocation of system asyncs can be temporarily disabled by | |
98 | calling @code{call-with-blocked-asyncs}. This function works by | |
99 | temporarily increasing the @emph{async blocking level} of the current | |
100 | thread while a given procedure is running. The blocking level starts | |
101 | out at zero, and whenever a safe point is reached, a blocking level | |
102 | greater than zero will prevent the execution of queued asyncs. | |
103 | ||
104 | Analogously, the procedure @code{call-with-unblocked-asyncs} will | |
105 | temporarily decrease the blocking level of the current thread. You | |
106 | can use it when you want to disable asyncs by default and only allow | |
107 | them temporarily. | |
108 | ||
109 | In addition to the C versions of @code{call-with-blocked-asyncs} and | |
110 | @code{call-with-unblocked-asyncs}, C code can use | |
661ae7ab MV |
111 | @code{scm_dynwind_block_asyncs} and @code{scm_dynwind_unblock_asyncs} |
112 | inside a @dfn{dynamic context} (@pxref{Dynamic Wind}) to block or | |
113 | unblock system asyncs temporarily. | |
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114 | |
115 | @deffn {Scheme Procedure} system-async-mark proc [thread] | |
116 | @deffnx {C Function} scm_system_async_mark (proc) | |
117 | @deffnx {C Function} scm_system_async_mark_for_thread (proc, thread) | |
118 | Mark @var{proc} (a procedure with zero arguments) for future execution | |
119 | in @var{thread}. When @var{proc} has already been marked for | |
120 | @var{thread} but has not been executed yet, this call has no effect. | |
121 | When @var{thread} is omitted, the thread that called | |
122 | @code{system-async-mark} is used. | |
123 | ||
124 | This procedure is not safe to be called from signal handlers. Use | |
125 | @code{scm_sigaction} or @code{scm_sigaction_for_thread} to install | |
126 | signal handlers. | |
127 | @end deffn | |
128 | ||
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129 | @deffn {Scheme Procedure} call-with-blocked-asyncs proc |
130 | @deffnx {C Function} scm_call_with_blocked_asyncs (proc) | |
07d83abe MV |
131 | Call @var{proc} and block the execution of system asyncs by one level |
132 | for the current thread while it is running. Return the value returned | |
133 | by @var{proc}. For the first two variants, call @var{proc} with no | |
134 | arguments; for the third, call it with @var{data}. | |
135 | @end deffn | |
136 | ||
1021bb7a NJ |
137 | @deftypefn {C Function} {void *} scm_c_call_with_blocked_asyncs (void * (*proc) (void *data), void *data) |
138 | The same but with a C function @var{proc} instead of a Scheme thunk. | |
139 | @end deftypefn | |
140 | ||
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141 | @deffn {Scheme Procedure} call-with-unblocked-asyncs proc |
142 | @deffnx {C Function} scm_call_with_unblocked_asyncs (proc) | |
07d83abe MV |
143 | Call @var{proc} and unblock the execution of system asyncs by one |
144 | level for the current thread while it is running. Return the value | |
145 | returned by @var{proc}. For the first two variants, call @var{proc} | |
146 | with no arguments; for the third, call it with @var{data}. | |
147 | @end deffn | |
148 | ||
1021bb7a NJ |
149 | @deftypefn {C Function} {void *} scm_c_call_with_unblocked_asyncs (void *(*proc) (void *data), void *data) |
150 | The same but with a C function @var{proc} instead of a Scheme thunk. | |
151 | @end deftypefn | |
152 | ||
661ae7ab | 153 | @deftypefn {C Function} void scm_dynwind_block_asyncs () |
1021bb7a NJ |
154 | During the current dynwind context, increase the blocking of asyncs by |
155 | one level. This function must be used inside a pair of calls to | |
661ae7ab | 156 | @code{scm_dynwind_begin} and @code{scm_dynwind_end} (@pxref{Dynamic |
1021bb7a | 157 | Wind}). |
07d83abe MV |
158 | @end deftypefn |
159 | ||
661ae7ab | 160 | @deftypefn {C Function} void scm_dynwind_unblock_asyncs () |
1021bb7a NJ |
161 | During the current dynwind context, decrease the blocking of asyncs by |
162 | one level. This function must be used inside a pair of calls to | |
661ae7ab | 163 | @code{scm_dynwind_begin} and @code{scm_dynwind_end} (@pxref{Dynamic |
1021bb7a | 164 | Wind}). |
07d83abe MV |
165 | @end deftypefn |
166 | ||
167 | @node User asyncs | |
168 | @subsubsection User asyncs | |
169 | ||
170 | A user async is a pair of a thunk (a parameterless procedure) and a | |
171 | mark. Setting the mark on a user async will cause the thunk to be | |
172 | executed when the user async is passed to @code{run-asyncs}. Setting | |
173 | the mark more than once is satisfied by one execution of the thunk. | |
174 | ||
175 | User asyncs are created with @code{async}. They are marked with | |
176 | @code{async-mark}. | |
177 | ||
178 | @deffn {Scheme Procedure} async thunk | |
179 | @deffnx {C Function} scm_async (thunk) | |
180 | Create a new user async for the procedure @var{thunk}. | |
181 | @end deffn | |
182 | ||
183 | @deffn {Scheme Procedure} async-mark a | |
184 | @deffnx {C Function} scm_async_mark (a) | |
185 | Mark the user async @var{a} for future execution. | |
186 | @end deffn | |
187 | ||
188 | @deffn {Scheme Procedure} run-asyncs list_of_a | |
189 | @deffnx {C Function} scm_run_asyncs (list_of_a) | |
190 | Execute all thunks from the marked asyncs of the list @var{list_of_a}. | |
191 | @end deffn | |
192 | ||
07d83abe MV |
193 | @node Threads |
194 | @subsection Threads | |
195 | @cindex threads | |
196 | @cindex Guile threads | |
197 | @cindex POSIX threads | |
198 | ||
0d4e6ca3 LC |
199 | Guile supports POSIX threads, unless it was configured with |
200 | @code{--without-threads} or the host lacks POSIX thread support. When | |
201 | thread support is available, the @code{threads} feature is provided | |
202 | (@pxref{Feature Manipulation, @code{provided?}}). | |
203 | ||
204 | The procedures below manipulate Guile threads, which are wrappers around | |
205 | the system's POSIX threads. For application-level parallelism, using | |
206 | higher-level constructs, such as futures, is recommended | |
207 | (@pxref{Futures}). | |
208 | ||
cdf1ad3b MV |
209 | @deffn {Scheme Procedure} all-threads |
210 | @deffnx {C Function} scm_all_threads () | |
211 | Return a list of all threads. | |
212 | @end deffn | |
213 | ||
214 | @deffn {Scheme Procedure} current-thread | |
215 | @deffnx {C Function} scm_current_thread () | |
216 | Return the thread that called this function. | |
217 | @end deffn | |
07d83abe MV |
218 | |
219 | @c begin (texi-doc-string "guile" "call-with-new-thread") | |
23f2b9a3 | 220 | @deffn {Scheme Procedure} call-with-new-thread thunk [handler] |
b4fddbbe MV |
221 | Call @code{thunk} in a new thread and with a new dynamic state, |
222 | returning the new thread. The procedure @var{thunk} is called via | |
223 | @code{with-continuation-barrier}. | |
07d83abe | 224 | |
b4fddbbe MV |
225 | When @var{handler} is specified, then @var{thunk} is called from |
226 | within a @code{catch} with tag @code{#t} that has @var{handler} as its | |
227 | handler. This catch is established inside the continuation barrier. | |
07d83abe | 228 | |
b4fddbbe MV |
229 | Once @var{thunk} or @var{handler} returns, the return value is made |
230 | the @emph{exit value} of the thread and the thread is terminated. | |
07d83abe MV |
231 | @end deffn |
232 | ||
b4fddbbe MV |
233 | @deftypefn {C Function} SCM scm_spawn_thread (scm_t_catch_body body, void *body_data, scm_t_catch_handler handler, void *handler_data) |
234 | Call @var{body} in a new thread, passing it @var{body_data}, returning | |
235 | the new thread. The function @var{body} is called via | |
236 | @code{scm_c_with_continuation_barrier}. | |
237 | ||
238 | When @var{handler} is non-@code{NULL}, @var{body} is called via | |
239 | @code{scm_internal_catch} with tag @code{SCM_BOOL_T} that has | |
240 | @var{handler} and @var{handler_data} as the handler and its data. This | |
241 | catch is established inside the continuation barrier. | |
242 | ||
243 | Once @var{body} or @var{handler} returns, the return value is made the | |
244 | @emph{exit value} of the thread and the thread is terminated. | |
245 | @end deftypefn | |
246 | ||
6180e336 NJ |
247 | @deffn {Scheme Procedure} thread? obj |
248 | @deffnx {C Function} scm_thread_p (obj) | |
249 | Return @code{#t} iff @var{obj} is a thread; otherwise, return | |
250 | @code{#f}. | |
251 | @end deffn | |
252 | ||
07d83abe | 253 | @c begin (texi-doc-string "guile" "join-thread") |
6180e336 | 254 | @deffn {Scheme Procedure} join-thread thread [timeout [timeoutval]] |
300b1ae5 | 255 | @deffnx {C Function} scm_join_thread (thread) |
6180e336 | 256 | @deffnx {C Function} scm_join_thread_timed (thread, timeout, timeoutval) |
b4fddbbe MV |
257 | Wait for @var{thread} to terminate and return its exit value. Threads |
258 | that have not been created with @code{call-with-new-thread} or | |
74926120 | 259 | @code{scm_spawn_thread} have an exit value of @code{#f}. When |
6180e336 | 260 | @var{timeout} is given, it specifies a point in time where the waiting |
74926120 NJ |
261 | should be aborted. It can be either an integer as returned by |
262 | @code{current-time} or a pair as returned by @code{gettimeofday}. | |
263 | When the waiting is aborted, @var{timeoutval} is returned (if it is | |
6180e336 | 264 | specified; @code{#f} is returned otherwise). |
07d83abe MV |
265 | @end deffn |
266 | ||
cdf1ad3b MV |
267 | @deffn {Scheme Procedure} thread-exited? thread |
268 | @deffnx {C Function} scm_thread_exited_p (thread) | |
269 | Return @code{#t} iff @var{thread} has exited. | |
270 | @end deffn | |
271 | ||
07d83abe MV |
272 | @c begin (texi-doc-string "guile" "yield") |
273 | @deffn {Scheme Procedure} yield | |
274 | If one or more threads are waiting to execute, calling yield forces an | |
275 | immediate context switch to one of them. Otherwise, yield has no effect. | |
276 | @end deffn | |
277 | ||
07e02175 LC |
278 | @deffn {Scheme Procedure} cancel-thread thread |
279 | @deffnx {C Function} scm_cancel_thread (thread) | |
280 | Asynchronously notify @var{thread} to exit. Immediately after | |
281 | receiving this notification, @var{thread} will call its cleanup handler | |
282 | (if one has been set) and then terminate, aborting any evaluation that | |
283 | is in progress. | |
284 | ||
285 | Because Guile threads are isomorphic with POSIX threads, @var{thread} | |
286 | will not receive its cancellation signal until it reaches a cancellation | |
287 | point. See your operating system's POSIX threading documentation for | |
288 | more information on cancellation points; note that in Guile, unlike | |
289 | native POSIX threads, a thread can receive a cancellation notification | |
290 | while attempting to lock a mutex. | |
291 | @end deffn | |
292 | ||
293 | @deffn {Scheme Procedure} set-thread-cleanup! thread proc | |
294 | @deffnx {C Function} scm_set_thread_cleanup_x (thread, proc) | |
295 | Set @var{proc} as the cleanup handler for the thread @var{thread}. | |
296 | @var{proc}, which must be a thunk, will be called when @var{thread} | |
297 | exits, either normally or by being canceled. Thread cleanup handlers | |
298 | can be used to perform useful tasks like releasing resources, such as | |
299 | locked mutexes, when thread exit cannot be predicted. | |
300 | ||
301 | The return value of @var{proc} will be set as the @emph{exit value} of | |
302 | @var{thread}. | |
303 | ||
304 | To remove a cleanup handler, pass @code{#f} for @var{proc}. | |
305 | @end deffn | |
306 | ||
307 | @deffn {Scheme Procedure} thread-cleanup thread | |
308 | @deffnx {C Function} scm_thread_cleanup (thread) | |
309 | Return the cleanup handler currently installed for the thread | |
310 | @var{thread}. If no cleanup handler is currently installed, | |
311 | thread-cleanup returns @code{#f}. | |
312 | @end deffn | |
313 | ||
07d83abe MV |
314 | Higher level thread procedures are available by loading the |
315 | @code{(ice-9 threads)} module. These provide standardized | |
3cf066df | 316 | thread creation. |
07d83abe MV |
317 | |
318 | @deffn macro make-thread proc [args@dots{}] | |
319 | Apply @var{proc} to @var{args} in a new thread formed by | |
320 | @code{call-with-new-thread} using a default error handler that display | |
b4fddbbe MV |
321 | the error to the current error port. The @var{args@dots{}} |
322 | expressions are evaluated in the new thread. | |
07d83abe MV |
323 | @end deffn |
324 | ||
325 | @deffn macro begin-thread first [rest@dots{}] | |
326 | Evaluate forms @var{first} and @var{rest} in a new thread formed by | |
327 | @code{call-with-new-thread} using a default error handler that display | |
328 | the error to the current error port. | |
329 | @end deffn | |
330 | ||
2567692a MV |
331 | @node Mutexes and Condition Variables |
332 | @subsection Mutexes and Condition Variables | |
333 | @cindex mutex | |
334 | @cindex condition variable | |
335 | ||
336 | A mutex is a thread synchronization object, it can be used by threads | |
337 | to control access to a shared resource. A mutex can be locked to | |
338 | indicate a resource is in use, and other threads can then block on the | |
339 | mutex to wait for the resource (or can just test and do something else | |
340 | if not available). ``Mutex'' is short for ``mutual exclusion''. | |
341 | ||
342 | There are two types of mutexes in Guile, ``standard'' and | |
343 | ``recursive''. They're created by @code{make-mutex} and | |
344 | @code{make-recursive-mutex} respectively, the operation functions are | |
345 | then common to both. | |
346 | ||
347 | Note that for both types of mutex there's no protection against a | |
348 | ``deadly embrace''. For instance if one thread has locked mutex A and | |
349 | is waiting on mutex B, but another thread owns B and is waiting on A, | |
350 | then an endless wait will occur (in the current implementation). | |
351 | Acquiring requisite mutexes in a fixed order (like always A before B) | |
352 | in all threads is one way to avoid such problems. | |
353 | ||
354 | @sp 1 | |
6180e336 | 355 | @deffn {Scheme Procedure} make-mutex . flags |
2567692a | 356 | @deffnx {C Function} scm_make_mutex () |
9c9b203b | 357 | @deffnx {C Function} scm_make_mutex_with_flags (SCM flags) |
74926120 | 358 | Return a new mutex. It is initially unlocked. If @var{flags} is |
6180e336 | 359 | specified, it must be a list of symbols specifying configuration flags |
74926120 | 360 | for the newly-created mutex. The supported flags are: |
6180e336 NJ |
361 | @table @code |
362 | @item unchecked-unlock | |
363 | Unless this flag is present, a call to `unlock-mutex' on the returned | |
364 | mutex when it is already unlocked will cause an error to be signalled. | |
365 | ||
366 | @item allow-external-unlock | |
367 | Allow the returned mutex to be unlocked by the calling thread even if | |
368 | it was originally locked by a different thread. | |
369 | ||
370 | @item recursive | |
371 | The returned mutex will be recursive. | |
372 | ||
373 | @end table | |
374 | @end deffn | |
375 | ||
376 | @deffn {Scheme Procedure} mutex? obj | |
377 | @deffnx {C Function} scm_mutex_p (obj) | |
74926120 | 378 | Return @code{#t} iff @var{obj} is a mutex; otherwise, return |
6180e336 | 379 | @code{#f}. |
2567692a MV |
380 | @end deffn |
381 | ||
382 | @deffn {Scheme Procedure} make-recursive-mutex | |
383 | @deffnx {C Function} scm_make_recursive_mutex () | |
6180e336 NJ |
384 | Create a new recursive mutex. It is initially unlocked. Calling this |
385 | function is equivalent to calling `make-mutex' and specifying the | |
386 | @code{recursive} flag. | |
2567692a MV |
387 | @end deffn |
388 | ||
adc085f1 | 389 | @deffn {Scheme Procedure} lock-mutex mutex [timeout [owner]] |
2567692a | 390 | @deffnx {C Function} scm_lock_mutex (mutex) |
adc085f1 | 391 | @deffnx {C Function} scm_lock_mutex_timed (mutex, timeout, owner) |
74926120 | 392 | Lock @var{mutex}. If the mutex is already locked, then block and |
adc085f1 | 393 | return only when @var{mutex} has been acquired. |
2567692a | 394 | |
74926120 NJ |
395 | When @var{timeout} is given, it specifies a point in time where the |
396 | waiting should be aborted. It can be either an integer as returned | |
397 | by @code{current-time} or a pair as returned by @code{gettimeofday}. | |
398 | When the waiting is aborted, @code{#f} is returned. | |
6180e336 | 399 | |
adc085f1 | 400 | When @var{owner} is given, it specifies an owner for @var{mutex} other |
74926120 | 401 | than the calling thread. @var{owner} may also be @code{#f}, |
adc085f1 JG |
402 | indicating that the mutex should be locked but left unowned. |
403 | ||
2567692a MV |
404 | For standard mutexes (@code{make-mutex}), and error is signalled if |
405 | the thread has itself already locked @var{mutex}. | |
406 | ||
407 | For a recursive mutex (@code{make-recursive-mutex}), if the thread has | |
408 | itself already locked @var{mutex}, then a further @code{lock-mutex} | |
409 | call increments the lock count. An additional @code{unlock-mutex} | |
410 | will be required to finally release. | |
411 | ||
6180e336 | 412 | If @var{mutex} was locked by a thread that exited before unlocking it, |
74926120 | 413 | the next attempt to lock @var{mutex} will succeed, but |
6180e336 NJ |
414 | @code{abandoned-mutex-error} will be signalled. |
415 | ||
2567692a MV |
416 | When a system async (@pxref{System asyncs}) is activated for a thread |
417 | blocked in @code{lock-mutex}, the wait is interrupted and the async is | |
418 | executed. When the async returns, the wait resumes. | |
419 | @end deffn | |
420 | ||
661ae7ab MV |
421 | @deftypefn {C Function} void scm_dynwind_lock_mutex (SCM mutex) |
422 | Arrange for @var{mutex} to be locked whenever the current dynwind | |
423 | context is entered and to be unlocked when it is exited. | |
2567692a | 424 | @end deftypefn |
74926120 | 425 | |
2567692a MV |
426 | @deffn {Scheme Procedure} try-mutex mx |
427 | @deffnx {C Function} scm_try_mutex (mx) | |
428 | Try to lock @var{mutex} as per @code{lock-mutex}. If @var{mutex} can | |
429 | be acquired immediately then this is done and the return is @code{#t}. | |
430 | If @var{mutex} is locked by some other thread then nothing is done and | |
431 | the return is @code{#f}. | |
432 | @end deffn | |
433 | ||
6180e336 | 434 | @deffn {Scheme Procedure} unlock-mutex mutex [condvar [timeout]] |
2567692a | 435 | @deffnx {C Function} scm_unlock_mutex (mutex) |
6180e336 NJ |
436 | @deffnx {C Function} scm_unlock_mutex_timed (mutex, condvar, timeout) |
437 | Unlock @var{mutex}. An error is signalled if @var{mutex} is not locked | |
74926120 | 438 | and was not created with the @code{unchecked-unlock} flag set, or if |
6180e336 NJ |
439 | @var{mutex} is locked by a thread other than the calling thread and was |
440 | not created with the @code{allow-external-unlock} flag set. | |
441 | ||
442 | If @var{condvar} is given, it specifies a condition variable upon | |
443 | which the calling thread will wait to be signalled before returning. | |
74926120 | 444 | (This behavior is very similar to that of |
6180e336 NJ |
445 | @code{wait-condition-variable}, except that the mutex is left in an |
446 | unlocked state when the function returns.) | |
447 | ||
74926120 NJ |
448 | When @var{timeout} is also given, it specifies a point in time where |
449 | the waiting should be aborted. It can be either an integer as | |
450 | returned by @code{current-time} or a pair as returned by | |
451 | @code{gettimeofday}. When the waiting is aborted, @code{#f} is | |
6180e336 | 452 | returned. Otherwise the function returns @code{#t}. |
2567692a MV |
453 | @end deffn |
454 | ||
adc085f1 JG |
455 | @deffn {Scheme Procedure} mutex-owner mutex |
456 | @deffnx {C Function} scm_mutex_owner (mutex) | |
74926120 | 457 | Return the current owner of @var{mutex}, in the form of a thread or |
adc085f1 JG |
458 | @code{#f} (indicating no owner). Note that a mutex may be unowned but |
459 | still locked. | |
460 | @end deffn | |
461 | ||
462 | @deffn {Scheme Procedure} mutex-level mutex | |
463 | @deffnx {C Function} scm_mutex_level (mutex) | |
464 | Return the current lock level of @var{mutex}. If @var{mutex} is | |
465 | currently unlocked, this value will be 0; otherwise, it will be the | |
466 | number of times @var{mutex} has been recursively locked by its current | |
467 | owner. | |
468 | @end deffn | |
469 | ||
470 | @deffn {Scheme Procedure} mutex-locked? mutex | |
471 | @deffnx {C Function} scm_mutex_locked_p (mutex) | |
472 | Return @code{#t} if @var{mutex} is locked, regardless of ownership; | |
473 | otherwise, return @code{#f}. | |
474 | @end deffn | |
475 | ||
2567692a MV |
476 | @deffn {Scheme Procedure} make-condition-variable |
477 | @deffnx {C Function} scm_make_condition_variable () | |
478 | Return a new condition variable. | |
479 | @end deffn | |
480 | ||
6180e336 NJ |
481 | @deffn {Scheme Procedure} condition-variable? obj |
482 | @deffnx {C Function} scm_condition_variable_p (obj) | |
74926120 | 483 | Return @code{#t} iff @var{obj} is a condition variable; otherwise, |
6180e336 NJ |
484 | return @code{#f}. |
485 | @end deffn | |
486 | ||
2567692a MV |
487 | @deffn {Scheme Procedure} wait-condition-variable condvar mutex [time] |
488 | @deffnx {C Function} scm_wait_condition_variable (condvar, mutex, time) | |
489 | Wait until @var{condvar} has been signalled. While waiting, | |
490 | @var{mutex} is atomically unlocked (as with @code{unlock-mutex}) and | |
491 | is locked again when this function returns. When @var{time} is given, | |
492 | it specifies a point in time where the waiting should be aborted. It | |
493 | can be either a integer as returned by @code{current-time} or a pair | |
494 | as returned by @code{gettimeofday}. When the waiting is aborted, | |
495 | @code{#f} is returned. When the condition variable has in fact been | |
496 | signalled, @code{#t} is returned. The mutex is re-locked in any case | |
497 | before @code{wait-condition-variable} returns. | |
498 | ||
499 | When a system async is activated for a thread that is blocked in a | |
500 | call to @code{wait-condition-variable}, the waiting is interrupted, | |
501 | the mutex is locked, and the async is executed. When the async | |
502 | returns, the mutex is unlocked again and the waiting is resumed. When | |
503 | the thread block while re-acquiring the mutex, execution of asyncs is | |
504 | blocked. | |
505 | @end deffn | |
506 | ||
507 | @deffn {Scheme Procedure} signal-condition-variable condvar | |
508 | @deffnx {C Function} scm_signal_condition_variable (condvar) | |
509 | Wake up one thread that is waiting for @var{condvar}. | |
510 | @end deffn | |
511 | ||
512 | @deffn {Scheme Procedure} broadcast-condition-variable condvar | |
513 | @deffnx {C Function} scm_broadcast_condition_variable (condvar) | |
514 | Wake up all threads that are waiting for @var{condvar}. | |
515 | @end deffn | |
516 | ||
517 | @sp 1 | |
518 | The following are higher level operations on mutexes. These are | |
519 | available from | |
520 | ||
521 | @example | |
522 | (use-modules (ice-9 threads)) | |
523 | @end example | |
524 | ||
525 | @deffn macro with-mutex mutex [body@dots{}] | |
526 | Lock @var{mutex}, evaluate the @var{body} forms, then unlock | |
527 | @var{mutex}. The return value is the return from the last @var{body} | |
528 | form. | |
529 | ||
530 | The lock, body and unlock form the branches of a @code{dynamic-wind} | |
531 | (@pxref{Dynamic Wind}), so @var{mutex} is automatically unlocked if an | |
532 | error or new continuation exits @var{body}, and is re-locked if | |
533 | @var{body} is re-entered by a captured continuation. | |
534 | @end deffn | |
535 | ||
536 | @deffn macro monitor body@dots{} | |
537 | Evaluate the @var{body} forms, with a mutex locked so only one thread | |
538 | can execute that code at any one time. The return value is the return | |
539 | from the last @var{body} form. | |
540 | ||
541 | Each @code{monitor} form has its own private mutex and the locking and | |
542 | evaluation is as per @code{with-mutex} above. A standard mutex | |
543 | (@code{make-mutex}) is used, which means @var{body} must not | |
544 | recursively re-enter the @code{monitor} form. | |
545 | ||
546 | The term ``monitor'' comes from operating system theory, where it | |
547 | means a particular bit of code managing access to some resource and | |
548 | which only ever executes on behalf of one process at any one time. | |
549 | @end deffn | |
550 | ||
551 | ||
b4fddbbe MV |
552 | @node Blocking |
553 | @subsection Blocking in Guile Mode | |
07d83abe | 554 | |
d3d66147 LC |
555 | Up to Guile version 1.8, a thread blocked in guile mode would prevent |
556 | the garbage collector from running. Thus threads had to explicitly | |
557 | leave guile mode with @code{scm_without_guile ()} before making a | |
558 | potentially blocking call such as a mutex lock, a @code{select ()} | |
559 | system call, etc. The following functions could be used to temporarily | |
560 | leave guile mode or to perform some common blocking operations in a | |
561 | supported way. | |
562 | ||
563 | Starting from Guile 2.0, blocked threads no longer hinder garbage | |
564 | collection. Thus, the functions below are not needed anymore. They can | |
565 | still be used to inform the GC that a thread is about to block, giving | |
566 | it a (small) optimization opportunity for ``stop the world'' garbage | |
567 | collections, should they occur while the thread is blocked. | |
07d83abe | 568 | |
54428bb8 MV |
569 | @deftypefn {C Function} {void *} scm_without_guile (void *(*func) (void *), void *data) |
570 | Leave guile mode, call @var{func} on @var{data}, enter guile mode and | |
571 | return the result of calling @var{func}. | |
07d83abe | 572 | |
b4fddbbe | 573 | While a thread has left guile mode, it must not call any libguile |
54428bb8 MV |
574 | functions except @code{scm_with_guile} or @code{scm_without_guile} and |
575 | must not use any libguile macros. Also, local variables of type | |
576 | @code{SCM} that are allocated while not in guile mode are not | |
577 | protected from the garbage collector. | |
578 | ||
579 | When used from non-guile mode, calling @code{scm_without_guile} is | |
580 | still allowed: it simply calls @var{func}. In that way, you can leave | |
581 | guile mode without having to know whether the current thread is in | |
582 | guile mode or not. | |
07d83abe MV |
583 | @end deftypefn |
584 | ||
b4fddbbe MV |
585 | @deftypefn {C Function} int scm_pthread_mutex_lock (pthread_mutex_t *mutex) |
586 | Like @code{pthread_mutex_lock}, but leaves guile mode while waiting for | |
587 | the mutex. | |
07d83abe MV |
588 | @end deftypefn |
589 | ||
b4fddbbe MV |
590 | @deftypefn {C Function} int scm_pthread_cond_wait (pthread_cond_t *cond, pthread_mutex_t *mutex) |
591 | @deftypefnx {C Function} int scm_pthread_cond_timedwait (pthread_cond_t *cond, pthread_mutex_t *mutex, struct timespec *abstime) | |
592 | Like @code{pthread_cond_wait} and @code{pthread_cond_timedwait}, but | |
593 | leaves guile mode while waiting for the condition variable. | |
07d83abe MV |
594 | @end deftypefn |
595 | ||
b4fddbbe MV |
596 | @deftypefn {C Function} int scm_std_select (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout) |
597 | Like @code{select} but leaves guile mode while waiting. Also, the | |
598 | delivery of a system async causes this function to be interrupted with | |
599 | error code @code{EINTR}. | |
07d83abe MV |
600 | @end deftypefn |
601 | ||
b4fddbbe MV |
602 | @deftypefn {C Function} {unsigned int} scm_std_sleep ({unsigned int} seconds) |
603 | Like @code{sleep}, but leaves guile mode while sleeping. Also, the | |
604 | delivery of a system async causes this function to be interrupted. | |
07d83abe MV |
605 | @end deftypefn |
606 | ||
b4fddbbe MV |
607 | @deftypefn {C Function} {unsigned long} scm_std_usleep ({unsigned long} usecs) |
608 | Like @code{usleep}, but leaves guile mode while sleeping. Also, the | |
609 | delivery of a system async causes this function to be interrupted. | |
07d83abe MV |
610 | @end deftypefn |
611 | ||
07d83abe | 612 | |
2567692a MV |
613 | @node Critical Sections |
614 | @subsection Critical Sections | |
615 | ||
616 | @deffn {C Macro} SCM_CRITICAL_SECTION_START | |
617 | @deffnx {C Macro} SCM_CRITICAL_SECTION_END | |
618 | These two macros can be used to delimit a critical section. | |
619 | Syntactically, they are both statements and need to be followed | |
620 | immediately by a semicolon. | |
621 | ||
622 | Executing @code{SCM_CRITICAL_SECTION_START} will lock a recursive | |
623 | mutex and block the executing of system asyncs. Executing | |
624 | @code{SCM_CRITICAL_SECTION_END} will unblock the execution of system | |
625 | asyncs and unlock the mutex. Thus, the code that executes between | |
626 | these two macros can only be executed in one thread at any one time | |
627 | and no system asyncs will run. However, because the mutex is a | |
628 | recursive one, the code might still be reentered by the same thread. | |
629 | You must either allow for this or avoid it, both by careful coding. | |
630 | ||
631 | On the other hand, critical sections delimited with these macros can | |
632 | be nested since the mutex is recursive. | |
633 | ||
634 | You must make sure that for each @code{SCM_CRITICAL_SECTION_START}, | |
635 | the corresponding @code{SCM_CRITICAL_SECTION_END} is always executed. | |
636 | This means that no non-local exit (such as a signalled error) might | |
637 | happen, for example. | |
638 | @end deffn | |
639 | ||
661ae7ab MV |
640 | @deftypefn {C Function} void scm_dynwind_critical_section (SCM mutex) |
641 | Call @code{scm_dynwind_lock_mutex} on @var{mutex} and call | |
642 | @code{scm_dynwind_block_asyncs}. When @var{mutex} is false, a recursive | |
2567692a MV |
643 | mutex provided by Guile is used instead. |
644 | ||
661ae7ab MV |
645 | The effect of a call to @code{scm_dynwind_critical_section} is that |
646 | the current dynwind context (@pxref{Dynamic Wind}) turns into a | |
647 | critical section. Because of the locked mutex, no second thread can | |
648 | enter it concurrently and because of the blocked asyncs, no system | |
649 | async can reenter it from the current thread. | |
2567692a MV |
650 | |
651 | When the current thread reenters the critical section anyway, the kind | |
652 | of @var{mutex} determines what happens: When @var{mutex} is recursive, | |
653 | the reentry is allowed. When it is a normal mutex, an error is | |
654 | signalled. | |
655 | @end deftypefn | |
656 | ||
657 | ||
b4fddbbe MV |
658 | @node Fluids and Dynamic States |
659 | @subsection Fluids and Dynamic States | |
07d83abe MV |
660 | |
661 | @cindex fluids | |
662 | ||
b4fddbbe MV |
663 | A @emph{fluid} is an object that can store one value per @emph{dynamic |
664 | state}. Each thread has a current dynamic state, and when accessing a | |
665 | fluid, this current dynamic state is used to provide the actual value. | |
666 | In this way, fluids can be used for thread local storage, but they are | |
667 | in fact more flexible: dynamic states are objects of their own and can | |
668 | be made current for more than one thread at the same time, or only be | |
669 | made current temporarily, for example. | |
670 | ||
671 | Fluids can also be used to simulate the desirable effects of | |
672 | dynamically scoped variables. Dynamically scoped variables are useful | |
673 | when you want to set a variable to a value during some dynamic extent | |
674 | in the execution of your program and have them revert to their | |
675 | original value when the control flow is outside of this dynamic | |
676 | extent. See the description of @code{with-fluids} below for details. | |
07d83abe MV |
677 | |
678 | New fluids are created with @code{make-fluid} and @code{fluid?} is | |
679 | used for testing whether an object is actually a fluid. The values | |
680 | stored in a fluid can be accessed with @code{fluid-ref} and | |
681 | @code{fluid-set!}. | |
682 | ||
683 | @deffn {Scheme Procedure} make-fluid | |
684 | @deffnx {C Function} scm_make_fluid () | |
685 | Return a newly created fluid. | |
b4fddbbe MV |
686 | Fluids are objects that can hold one |
687 | value per dynamic state. That is, modifications to this value are | |
688 | only visible to code that executes with the same dynamic state as | |
689 | the modifying code. When a new dynamic state is constructed, it | |
690 | inherits the values from its parent. Because each thread normally executes | |
691 | with its own dynamic state, you can use fluids for thread local storage. | |
07d83abe MV |
692 | @end deffn |
693 | ||
694 | @deffn {Scheme Procedure} fluid? obj | |
695 | @deffnx {C Function} scm_fluid_p (obj) | |
696 | Return @code{#t} iff @var{obj} is a fluid; otherwise, return | |
697 | @code{#f}. | |
698 | @end deffn | |
699 | ||
700 | @deffn {Scheme Procedure} fluid-ref fluid | |
701 | @deffnx {C Function} scm_fluid_ref (fluid) | |
702 | Return the value associated with @var{fluid} in the current | |
703 | dynamic root. If @var{fluid} has not been set, then return | |
704 | @code{#f}. | |
705 | @end deffn | |
706 | ||
707 | @deffn {Scheme Procedure} fluid-set! fluid value | |
708 | @deffnx {C Function} scm_fluid_set_x (fluid, value) | |
709 | Set the value associated with @var{fluid} in the current dynamic root. | |
710 | @end deffn | |
711 | ||
712 | @code{with-fluids*} temporarily changes the values of one or more fluids, | |
713 | so that the given procedure and each procedure called by it access the | |
714 | given values. After the procedure returns, the old values are restored. | |
715 | ||
cdf1ad3b MV |
716 | @deffn {Scheme Procedure} with-fluid* fluid value thunk |
717 | @deffnx {C Function} scm_with_fluid (fluid, value, thunk) | |
718 | Set @var{fluid} to @var{value} temporarily, and call @var{thunk}. | |
719 | @var{thunk} must be a procedure with no argument. | |
720 | @end deffn | |
721 | ||
07d83abe MV |
722 | @deffn {Scheme Procedure} with-fluids* fluids values thunk |
723 | @deffnx {C Function} scm_with_fluids (fluids, values, thunk) | |
724 | Set @var{fluids} to @var{values} temporary, and call @var{thunk}. | |
725 | @var{fluids} must be a list of fluids and @var{values} must be the | |
726 | same number of their values to be applied. Each substitution is done | |
727 | in the order given. @var{thunk} must be a procedure with no argument. | |
728 | it is called inside a @code{dynamic-wind} and the fluids are | |
729 | set/restored when control enter or leaves the established dynamic | |
730 | extent. | |
731 | @end deffn | |
732 | ||
733 | @deffn {Scheme Macro} with-fluids ((fluid value) ...) body... | |
734 | Execute @var{body...} while each @var{fluid} is set to the | |
735 | corresponding @var{value}. Both @var{fluid} and @var{value} are | |
736 | evaluated and @var{fluid} must yield a fluid. @var{body...} is | |
737 | executed inside a @code{dynamic-wind} and the fluids are set/restored | |
738 | when control enter or leaves the established dynamic extent. | |
739 | @end deffn | |
740 | ||
741 | @deftypefn {C Function} SCM scm_c_with_fluids (SCM fluids, SCM vals, SCM (*cproc)(void *), void *data) | |
742 | @deftypefnx {C Function} SCM scm_c_with_fluid (SCM fluid, SCM val, SCM (*cproc)(void *), void *data) | |
743 | The function @code{scm_c_with_fluids} is like @code{scm_with_fluids} | |
744 | except that it takes a C function to call instead of a Scheme thunk. | |
745 | ||
746 | The function @code{scm_c_with_fluid} is similar but only allows one | |
747 | fluid to be set instead of a list. | |
748 | @end deftypefn | |
749 | ||
661ae7ab | 750 | @deftypefn {C Function} void scm_dynwind_fluid (SCM fluid, SCM val) |
07d83abe | 751 | This function must be used inside a pair of calls to |
661ae7ab MV |
752 | @code{scm_dynwind_begin} and @code{scm_dynwind_end} (@pxref{Dynamic |
753 | Wind}). During the dynwind context, the fluid @var{fluid} is set to | |
754 | @var{val}. | |
07d83abe MV |
755 | |
756 | More precisely, the value of the fluid is swapped with a `backup' | |
661ae7ab MV |
757 | value whenever the dynwind context is entered or left. The backup |
758 | value is initialized with the @var{val} argument. | |
07d83abe MV |
759 | @end deftypefn |
760 | ||
b4fddbbe MV |
761 | @deffn {Scheme Procedure} make-dynamic-state [parent] |
762 | @deffnx {C Function} scm_make_dynamic_state (parent) | |
763 | Return a copy of the dynamic state object @var{parent} | |
764 | or of the current dynamic state when @var{parent} is omitted. | |
765 | @end deffn | |
766 | ||
767 | @deffn {Scheme Procedure} dynamic-state? obj | |
768 | @deffnx {C Function} scm_dynamic_state_p (obj) | |
769 | Return @code{#t} if @var{obj} is a dynamic state object; | |
770 | return @code{#f} otherwise. | |
771 | @end deffn | |
772 | ||
773 | @deftypefn {C Procedure} int scm_is_dynamic_state (SCM obj) | |
774 | Return non-zero if @var{obj} is a dynamic state object; | |
775 | return zero otherwise. | |
776 | @end deftypefn | |
777 | ||
778 | @deffn {Scheme Procedure} current-dynamic-state | |
779 | @deffnx {C Function} scm_current_dynamic_state () | |
780 | Return the current dynamic state object. | |
781 | @end deffn | |
782 | ||
783 | @deffn {Scheme Procedure} set-current-dynamic-state state | |
784 | @deffnx {C Function} scm_set_current_dynamic_state (state) | |
785 | Set the current dynamic state object to @var{state} | |
786 | and return the previous current dynamic state object. | |
787 | @end deffn | |
788 | ||
789 | @deffn {Scheme Procedure} with-dynamic-state state proc | |
790 | @deffnx {C Function} scm_with_dynamic_state (state, proc) | |
791 | Call @var{proc} while @var{state} is the current dynamic | |
792 | state object. | |
793 | @end deffn | |
794 | ||
661ae7ab MV |
795 | @deftypefn {C Procedure} void scm_dynwind_current_dynamic_state (SCM state) |
796 | Set the current dynamic state to @var{state} for the current dynwind | |
797 | context. | |
b4fddbbe MV |
798 | @end deftypefn |
799 | ||
c2110081 | 800 | @deftypefn {C Procedure} {void *} scm_c_with_dynamic_state (SCM state, void *(*func)(void *), void *data) |
b4fddbbe MV |
801 | Like @code{scm_with_dynamic_state}, but call @var{func} with |
802 | @var{data}. | |
803 | @end deftypefn | |
804 | ||
0d4e6ca3 LC |
805 | @node Futures |
806 | @subsection Futures | |
807 | @cindex futures | |
808 | @cindex fine-grain parallelism | |
809 | @cindex parallelism | |
810 | ||
811 | The @code{(ice-9 futures)} module provides @dfn{futures}, a construct | |
812 | for fine-grain parallelism. A future is a wrapper around an expression | |
813 | whose computation may occur in parallel with the code of the calling | |
814 | thread, and possibly in parallel with other futures. Like promises, | |
815 | futures are essentially proxies that can be queried to obtain the value | |
816 | of the enclosed expression: | |
817 | ||
818 | @lisp | |
819 | (touch (future (+ 2 3))) | |
820 | @result{} 5 | |
821 | @end lisp | |
822 | ||
823 | However, unlike promises, the expression associated with a future may be | |
824 | evaluated on another CPU core, should one be available. This supports | |
825 | @dfn{fine-grain parallelism}, because even relatively small computations | |
826 | can be embedded in futures. Consider this sequential code: | |
827 | ||
828 | @lisp | |
829 | (define (find-prime lst1 lst2) | |
830 | (or (find prime? lst1) | |
831 | (find prime? lst2))) | |
832 | @end lisp | |
833 | ||
834 | The two arms of @code{or} are potentially computation-intensive. They | |
835 | are independent of one another, yet, they are evaluated sequentially | |
836 | when the first one returns @code{#f}. Using futures, one could rewrite | |
837 | it like this: | |
838 | ||
839 | @lisp | |
840 | (define (find-prime lst1 lst2) | |
841 | (let ((f (future (find prime? lst2)))) | |
842 | (or (find prime? lst1) | |
843 | (touch f)))) | |
844 | @end lisp | |
845 | ||
846 | This preserves the semantics of @code{find-prime}. On a multi-core | |
847 | machine, though, the computation of @code{(find prime? lst2)} may be | |
848 | done in parallel with that of the other @code{find} call, which can | |
849 | reduce the execution time of @code{find-prime}. | |
850 | ||
851 | Guile's futures are implemented on top of POSIX threads | |
852 | (@pxref{Threads}). Internally, a fixed-size pool of threads is used to | |
853 | evaluate futures, such that offloading the evaluation of an expression | |
854 | to another thread doesn't incur thread creation costs. By default, the | |
855 | pool contains one thread per CPU core, minus one, to account for the | |
856 | main thread. | |
857 | ||
858 | @deffn {Scheme Syntax} future exp | |
859 | Return a future for expression @var{exp}. This is equivalent to: | |
860 | ||
861 | @lisp | |
862 | (make-future (lambda () exp)) | |
863 | @end lisp | |
864 | @end deffn | |
865 | ||
866 | @deffn {Scheme Procedure} make-future thunk | |
867 | Return a future for @var{thunk}, a zero-argument procedure. | |
868 | ||
869 | This procedure returns immediately. Execution of @var{thunk} may begin | |
870 | in parallel with the calling thread's computations, if idle CPU cores | |
871 | are available, or it may start when @code{touch} is invoked on the | |
872 | returned future. | |
873 | ||
874 | If the execution of @var{thunk} throws an exception, that exception will | |
875 | be re-thrown when @code{touch} is invoked on the returned future. | |
876 | @end deffn | |
877 | ||
878 | @deffn {Scheme Procedure} future? obj | |
879 | Return @code{#t} if @var{obj} is a future. | |
880 | @end deffn | |
881 | ||
882 | @deffn {Scheme Procedure} touch f | |
883 | Return the result of the expression embedded in future @var{f}. | |
884 | ||
885 | If the result was already computed in parallel, @code{touch} returns | |
886 | instantaneously. Otherwise, it waits for the computation to complete, | |
887 | if it already started, or initiates it. | |
888 | @end deffn | |
889 | ||
890 | ||
07d83abe MV |
891 | @node Parallel Forms |
892 | @subsection Parallel forms | |
893 | @cindex parallel forms | |
894 | ||
895 | The functions described in this section are available from | |
896 | ||
897 | @example | |
898 | (use-modules (ice-9 threads)) | |
899 | @end example | |
900 | ||
901 | @deffn syntax parallel expr1 @dots{} exprN | |
af1323c5 | 902 | Evaluate each @var{expr} expression in parallel, each in its own thread. |
07d83abe MV |
903 | Return the results as a set of @var{N} multiple values |
904 | (@pxref{Multiple Values}). | |
905 | @end deffn | |
906 | ||
907 | @deffn syntax letpar ((var1 expr1) @dots{} (varN exprN)) body@dots{} | |
af1323c5 | 908 | Evaluate each @var{expr} in parallel, each in its own thread, then bind |
07d83abe MV |
909 | the results to the corresponding @var{var} variables and evaluate |
910 | @var{body}. | |
911 | ||
912 | @code{letpar} is like @code{let} (@pxref{Local Bindings}), but all the | |
913 | expressions for the bindings are evaluated in parallel. | |
914 | @end deffn | |
915 | ||
916 | @deffn {Scheme Procedure} par-map proc lst1 @dots{} lstN | |
917 | @deffnx {Scheme Procedure} par-for-each proc lst1 @dots{} lstN | |
918 | Call @var{proc} on the elements of the given lists. @code{par-map} | |
919 | returns a list comprising the return values from @var{proc}. | |
920 | @code{par-for-each} returns an unspecified value, but waits for all | |
921 | calls to complete. | |
922 | ||
923 | The @var{proc} calls are @code{(@var{proc} @var{elem1} @dots{} | |
924 | @var{elemN})}, where each @var{elem} is from the corresponding | |
925 | @var{lst}. Each @var{lst} must be the same length. The calls are | |
af1323c5 | 926 | made in parallel, each in its own thread. |
07d83abe MV |
927 | |
928 | These functions are like @code{map} and @code{for-each} (@pxref{List | |
929 | Mapping}), but make their @var{proc} calls in parallel. | |
930 | @end deffn | |
931 | ||
932 | @deffn {Scheme Procedure} n-par-map n proc lst1 @dots{} lstN | |
933 | @deffnx {Scheme Procedure} n-par-for-each n proc lst1 @dots{} lstN | |
934 | Call @var{proc} on the elements of the given lists, in the same way as | |
935 | @code{par-map} and @code{par-for-each} above, but use no more than | |
af1323c5 | 936 | @var{n} threads at any one time. The order in which calls are |
07d83abe MV |
937 | initiated within that threads limit is unspecified. |
938 | ||
939 | These functions are good for controlling resource consumption if | |
940 | @var{proc} calls might be costly, or if there are many to be made. On | |
941 | a dual-CPU system for instance @math{@var{n}=4} might be enough to | |
942 | keep the CPUs utilized, and not consume too much memory. | |
943 | @end deffn | |
944 | ||
945 | @deffn {Scheme Procedure} n-for-each-par-map n sproc pproc lst1 @dots{} lstN | |
946 | Apply @var{pproc} to the elements of the given lists, and apply | |
947 | @var{sproc} to each result returned by @var{pproc}. The final return | |
948 | value is unspecified, but all calls will have been completed before | |
949 | returning. | |
950 | ||
951 | The calls made are @code{(@var{sproc} (@var{pproc} @var{elem1} @dots{} | |
952 | @var{elemN}))}, where each @var{elem} is from the corresponding | |
953 | @var{lst}. Each @var{lst} must have the same number of elements. | |
954 | ||
af1323c5 KR |
955 | The @var{pproc} calls are made in parallel, in separate threads. No more |
956 | than @var{n} threads are used at any one time. The order in which | |
07d83abe MV |
957 | @var{pproc} calls are initiated within that limit is unspecified. |
958 | ||
959 | The @var{sproc} calls are made serially, in list element order, one at | |
960 | a time. @var{pproc} calls on later elements may execute in parallel | |
961 | with the @var{sproc} calls. Exactly which thread makes each | |
962 | @var{sproc} call is unspecified. | |
963 | ||
964 | This function is designed for individual calculations that can be done | |
965 | in parallel, but with results needing to be handled serially, for | |
966 | instance to write them to a file. The @var{n} limit on threads | |
967 | controls system resource usage when there are many calculations or | |
968 | when they might be costly. | |
969 | ||
970 | It will be seen that @code{n-for-each-par-map} is like a combination | |
971 | of @code{n-par-map} and @code{for-each}, | |
972 | ||
973 | @example | |
af1323c5 | 974 | (for-each sproc (n-par-map n pproc lst1 ... lstN)) |
07d83abe MV |
975 | @end example |
976 | ||
977 | @noindent | |
978 | But the actual implementation is more efficient since each @var{sproc} | |
979 | call, in turn, can be initiated once the relevant @var{pproc} call has | |
980 | completed, it doesn't need to wait for all to finish. | |
981 | @end deffn | |
982 | ||
983 | ||
3cf066df | 984 | |
07d83abe MV |
985 | @c Local Variables: |
986 | @c TeX-master: "guile.texi" | |
987 | @c End: |