Line data Source code
1 : /*
2 : * Portable condition variable support for windows and pthreads.
3 : * Everything is inline, this header can be included where needed.
4 : *
5 : * APIs generally return 0 on success and non-zero on error,
6 : * and the caller needs to use its platform's error mechanism to
7 : * discover the error (errno, or GetLastError())
8 : *
9 : * Note that some implementations cannot distinguish between a
10 : * condition variable wait time-out and successful wait. Most often
11 : * the difference is moot anyway since the wait condition must be
12 : * re-checked.
13 : * PyCOND_TIMEDWAIT, in addition to returning negative on error,
14 : * thus returns 0 on regular success, 1 on timeout
15 : * or 2 if it can't tell.
16 : *
17 : * There are at least two caveats with using these condition variables,
18 : * due to the fact that they may be emulated with Semaphores on
19 : * Windows:
20 : * 1) While PyCOND_SIGNAL() will wake up at least one thread, we
21 : * cannot currently guarantee that it will be one of the threads
22 : * already waiting in a PyCOND_WAIT() call. It _could_ cause
23 : * the wakeup of a subsequent thread to try a PyCOND_WAIT(),
24 : * including the thread doing the PyCOND_SIGNAL() itself.
25 : * The same applies to PyCOND_BROADCAST(), if N threads are waiting
26 : * then at least N threads will be woken up, but not necessarily
27 : * those already waiting.
28 : * For this reason, don't make the scheduling assumption that a
29 : * specific other thread will get the wakeup signal
30 : * 2) The _mutex_ must be held when calling PyCOND_SIGNAL() and
31 : * PyCOND_BROADCAST().
32 : * While e.g. the posix standard strongly recommends that the mutex
33 : * associated with the condition variable is held when a
34 : * pthread_cond_signal() call is made, this is not a hard requirement,
35 : * although scheduling will not be "reliable" if it isn't. Here
36 : * the mutex is used for internal synchronization of the emulated
37 : * Condition Variable.
38 : */
39 :
40 : #ifndef _CONDVAR_IMPL_H_
41 : #define _CONDVAR_IMPL_H_
42 :
43 : #include "Python.h"
44 : #include "pycore_condvar.h"
45 :
46 : #ifdef _POSIX_THREADS
47 : /*
48 : * POSIX support
49 : */
50 :
51 : /* These private functions are implemented in Python/thread_pthread.h */
52 : int _PyThread_cond_init(PyCOND_T *cond);
53 : void _PyThread_cond_after(long long us, struct timespec *abs);
54 :
55 : /* The following functions return 0 on success, nonzero on error */
56 : #define PyMUTEX_INIT(mut) pthread_mutex_init((mut), NULL)
57 : #define PyMUTEX_FINI(mut) pthread_mutex_destroy(mut)
58 : #define PyMUTEX_LOCK(mut) pthread_mutex_lock(mut)
59 : #define PyMUTEX_UNLOCK(mut) pthread_mutex_unlock(mut)
60 :
61 : #define PyCOND_INIT(cond) _PyThread_cond_init(cond)
62 : #define PyCOND_FINI(cond) pthread_cond_destroy(cond)
63 : #define PyCOND_SIGNAL(cond) pthread_cond_signal(cond)
64 : #define PyCOND_BROADCAST(cond) pthread_cond_broadcast(cond)
65 : #define PyCOND_WAIT(cond, mut) pthread_cond_wait((cond), (mut))
66 :
67 : /* return 0 for success, 1 on timeout, -1 on error */
68 : Py_LOCAL_INLINE(int)
69 319760 : PyCOND_TIMEDWAIT(PyCOND_T *cond, PyMUTEX_T *mut, long long us)
70 : {
71 : struct timespec abs_timeout;
72 319760 : _PyThread_cond_after(us, &abs_timeout);
73 319760 : int ret = pthread_cond_timedwait(cond, mut, &abs_timeout);
74 319758 : if (ret == ETIMEDOUT) {
75 124778 : return 1;
76 : }
77 194980 : if (ret) {
78 0 : return -1;
79 : }
80 194980 : return 0;
81 : }
82 :
83 : #elif defined(NT_THREADS)
84 : /*
85 : * Windows (XP, 2003 server and later, as well as (hopefully) CE) support
86 : *
87 : * Emulated condition variables ones that work with XP and later, plus
88 : * example native support on VISTA and onwards.
89 : */
90 :
91 : #if _PY_EMULATED_WIN_CV
92 :
93 : /* The mutex is a CriticalSection object and
94 : The condition variables is emulated with the help of a semaphore.
95 :
96 : This implementation still has the problem that the threads woken
97 : with a "signal" aren't necessarily those that are already
98 : waiting. It corresponds to listing 2 in:
99 : http://birrell.org/andrew/papers/ImplementingCVs.pdf
100 :
101 : Generic emulations of the pthread_cond_* API using
102 : earlier Win32 functions can be found on the web.
103 : The following read can be give background information to these issues,
104 : but the implementations are all broken in some way.
105 : http://www.cse.wustl.edu/~schmidt/win32-cv-1.html
106 : */
107 :
108 : Py_LOCAL_INLINE(int)
109 : PyMUTEX_INIT(PyMUTEX_T *cs)
110 : {
111 : InitializeCriticalSection(cs);
112 : return 0;
113 : }
114 :
115 : Py_LOCAL_INLINE(int)
116 : PyMUTEX_FINI(PyMUTEX_T *cs)
117 : {
118 : DeleteCriticalSection(cs);
119 : return 0;
120 : }
121 :
122 : Py_LOCAL_INLINE(int)
123 : PyMUTEX_LOCK(PyMUTEX_T *cs)
124 : {
125 : EnterCriticalSection(cs);
126 : return 0;
127 : }
128 :
129 : Py_LOCAL_INLINE(int)
130 : PyMUTEX_UNLOCK(PyMUTEX_T *cs)
131 : {
132 : LeaveCriticalSection(cs);
133 : return 0;
134 : }
135 :
136 :
137 : Py_LOCAL_INLINE(int)
138 : PyCOND_INIT(PyCOND_T *cv)
139 : {
140 : /* A semaphore with a "large" max value, The positive value
141 : * is only needed to catch those "lost wakeup" events and
142 : * race conditions when a timed wait elapses.
143 : */
144 : cv->sem = CreateSemaphore(NULL, 0, 100000, NULL);
145 : if (cv->sem==NULL)
146 : return -1;
147 : cv->waiting = 0;
148 : return 0;
149 : }
150 :
151 : Py_LOCAL_INLINE(int)
152 : PyCOND_FINI(PyCOND_T *cv)
153 : {
154 : return CloseHandle(cv->sem) ? 0 : -1;
155 : }
156 :
157 : /* this implementation can detect a timeout. Returns 1 on timeout,
158 : * 0 otherwise (and -1 on error)
159 : */
160 : Py_LOCAL_INLINE(int)
161 : _PyCOND_WAIT_MS(PyCOND_T *cv, PyMUTEX_T *cs, DWORD ms)
162 : {
163 : DWORD wait;
164 : cv->waiting++;
165 : PyMUTEX_UNLOCK(cs);
166 : /* "lost wakeup bug" would occur if the caller were interrupted here,
167 : * but we are safe because we are using a semaphore which has an internal
168 : * count.
169 : */
170 : wait = WaitForSingleObjectEx(cv->sem, ms, FALSE);
171 : PyMUTEX_LOCK(cs);
172 : if (wait != WAIT_OBJECT_0)
173 : --cv->waiting;
174 : /* Here we have a benign race condition with PyCOND_SIGNAL.
175 : * When failure occurs or timeout, it is possible that
176 : * PyCOND_SIGNAL also decrements this value
177 : * and signals releases the mutex. This is benign because it
178 : * just means an extra spurious wakeup for a waiting thread.
179 : * ('waiting' corresponds to the semaphore's "negative" count and
180 : * we may end up with e.g. (waiting == -1 && sem.count == 1). When
181 : * a new thread comes along, it will pass right through, having
182 : * adjusted it to (waiting == 0 && sem.count == 0).
183 : */
184 :
185 : if (wait == WAIT_FAILED)
186 : return -1;
187 : /* return 0 on success, 1 on timeout */
188 : return wait != WAIT_OBJECT_0;
189 : }
190 :
191 : Py_LOCAL_INLINE(int)
192 : PyCOND_WAIT(PyCOND_T *cv, PyMUTEX_T *cs)
193 : {
194 : int result = _PyCOND_WAIT_MS(cv, cs, INFINITE);
195 : return result >= 0 ? 0 : result;
196 : }
197 :
198 : Py_LOCAL_INLINE(int)
199 : PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long long us)
200 : {
201 : return _PyCOND_WAIT_MS(cv, cs, (DWORD)(us/1000));
202 : }
203 :
204 : Py_LOCAL_INLINE(int)
205 : PyCOND_SIGNAL(PyCOND_T *cv)
206 : {
207 : /* this test allows PyCOND_SIGNAL to be a no-op unless required
208 : * to wake someone up, thus preventing an unbounded increase of
209 : * the semaphore's internal counter.
210 : */
211 : if (cv->waiting > 0) {
212 : /* notifying thread decreases the cv->waiting count so that
213 : * a delay between notify and actual wakeup of the target thread
214 : * doesn't cause a number of extra ReleaseSemaphore calls.
215 : */
216 : cv->waiting--;
217 : return ReleaseSemaphore(cv->sem, 1, NULL) ? 0 : -1;
218 : }
219 : return 0;
220 : }
221 :
222 : Py_LOCAL_INLINE(int)
223 : PyCOND_BROADCAST(PyCOND_T *cv)
224 : {
225 : int waiting = cv->waiting;
226 : if (waiting > 0) {
227 : cv->waiting = 0;
228 : return ReleaseSemaphore(cv->sem, waiting, NULL) ? 0 : -1;
229 : }
230 : return 0;
231 : }
232 :
233 : #else /* !_PY_EMULATED_WIN_CV */
234 :
235 : Py_LOCAL_INLINE(int)
236 : PyMUTEX_INIT(PyMUTEX_T *cs)
237 : {
238 : InitializeSRWLock(cs);
239 : return 0;
240 : }
241 :
242 : Py_LOCAL_INLINE(int)
243 : PyMUTEX_FINI(PyMUTEX_T *cs)
244 : {
245 : return 0;
246 : }
247 :
248 : Py_LOCAL_INLINE(int)
249 : PyMUTEX_LOCK(PyMUTEX_T *cs)
250 : {
251 : AcquireSRWLockExclusive(cs);
252 : return 0;
253 : }
254 :
255 : Py_LOCAL_INLINE(int)
256 : PyMUTEX_UNLOCK(PyMUTEX_T *cs)
257 : {
258 : ReleaseSRWLockExclusive(cs);
259 : return 0;
260 : }
261 :
262 :
263 : Py_LOCAL_INLINE(int)
264 : PyCOND_INIT(PyCOND_T *cv)
265 : {
266 : InitializeConditionVariable(cv);
267 : return 0;
268 : }
269 : Py_LOCAL_INLINE(int)
270 : PyCOND_FINI(PyCOND_T *cv)
271 : {
272 : return 0;
273 : }
274 :
275 : Py_LOCAL_INLINE(int)
276 : PyCOND_WAIT(PyCOND_T *cv, PyMUTEX_T *cs)
277 : {
278 : return SleepConditionVariableSRW(cv, cs, INFINITE, 0) ? 0 : -1;
279 : }
280 :
281 : /* This implementation makes no distinction about timeouts. Signal
282 : * 2 to indicate that we don't know.
283 : */
284 : Py_LOCAL_INLINE(int)
285 : PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long long us)
286 : {
287 : return SleepConditionVariableSRW(cv, cs, (DWORD)(us/1000), 0) ? 2 : -1;
288 : }
289 :
290 : Py_LOCAL_INLINE(int)
291 : PyCOND_SIGNAL(PyCOND_T *cv)
292 : {
293 : WakeConditionVariable(cv);
294 : return 0;
295 : }
296 :
297 : Py_LOCAL_INLINE(int)
298 : PyCOND_BROADCAST(PyCOND_T *cv)
299 : {
300 : WakeAllConditionVariable(cv);
301 : return 0;
302 : }
303 :
304 :
305 : #endif /* _PY_EMULATED_WIN_CV */
306 :
307 : #endif /* _POSIX_THREADS, NT_THREADS */
308 :
309 : #endif /* _CONDVAR_IMPL_H_ */
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