Merge commit 'v1.7.0' into jc/checkout-reflog-fix
[git] / compat / win32 / pthread.c
1 /*
2  * Copyright (C) 2009 Andrzej K. Haczewski <ahaczewski@gmail.com>
3  *
4  * DISCLAMER: The implementation is Git-specific, it is subset of original
5  * Pthreads API, without lots of other features that Git doesn't use.
6  * Git also makes sure that the passed arguments are valid, so there's
7  * no need for double-checking.
8  */
9
10 #include "../../git-compat-util.h"
11 #include "pthread.h"
12
13 #include <errno.h>
14 #include <limits.h>
15
16 static unsigned __stdcall win32_start_routine(void *arg)
17 {
18         pthread_t *thread = arg;
19         thread->arg = thread->start_routine(thread->arg);
20         return 0;
21 }
22
23 int pthread_create(pthread_t *thread, const void *unused,
24                    void *(*start_routine)(void*), void *arg)
25 {
26         thread->arg = arg;
27         thread->start_routine = start_routine;
28         thread->handle = (HANDLE)
29                 _beginthreadex(NULL, 0, win32_start_routine, thread, 0, NULL);
30
31         if (!thread->handle)
32                 return errno;
33         else
34                 return 0;
35 }
36
37 int win32_pthread_join(pthread_t *thread, void **value_ptr)
38 {
39         DWORD result = WaitForSingleObject(thread->handle, INFINITE);
40         switch (result) {
41                 case WAIT_OBJECT_0:
42                         if (value_ptr)
43                                 *value_ptr = thread->arg;
44                         return 0;
45                 case WAIT_ABANDONED:
46                         return EINVAL;
47                 default:
48                         return err_win_to_posix(GetLastError());
49         }
50 }
51
52 int pthread_cond_init(pthread_cond_t *cond, const void *unused)
53 {
54         cond->waiters = 0;
55         cond->was_broadcast = 0;
56         InitializeCriticalSection(&cond->waiters_lock);
57
58         cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
59         if (!cond->sema)
60                 die("CreateSemaphore() failed");
61
62         cond->continue_broadcast = CreateEvent(NULL,    /* security */
63                                 FALSE,                  /* auto-reset */
64                                 FALSE,                  /* not signaled */
65                                 NULL);                  /* name */
66         if (!cond->continue_broadcast)
67                 die("CreateEvent() failed");
68
69         return 0;
70 }
71
72 int pthread_cond_destroy(pthread_cond_t *cond)
73 {
74         CloseHandle(cond->sema);
75         CloseHandle(cond->continue_broadcast);
76         DeleteCriticalSection(&cond->waiters_lock);
77         return 0;
78 }
79
80 int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex)
81 {
82         int last_waiter;
83
84         EnterCriticalSection(&cond->waiters_lock);
85         cond->waiters++;
86         LeaveCriticalSection(&cond->waiters_lock);
87
88         /*
89          * Unlock external mutex and wait for signal.
90          * NOTE: we've held mutex locked long enough to increment
91          * waiters count above, so there's no problem with
92          * leaving mutex unlocked before we wait on semaphore.
93          */
94         LeaveCriticalSection(mutex);
95
96         /* let's wait - ignore return value */
97         WaitForSingleObject(cond->sema, INFINITE);
98
99         /*
100          * Decrease waiters count. If we are the last waiter, then we must
101          * notify the broadcasting thread that it can continue.
102          * But if we continued due to cond_signal, we do not have to do that
103          * because the signaling thread knows that only one waiter continued.
104          */
105         EnterCriticalSection(&cond->waiters_lock);
106         cond->waiters--;
107         last_waiter = cond->was_broadcast && cond->waiters == 0;
108         LeaveCriticalSection(&cond->waiters_lock);
109
110         if (last_waiter) {
111                 /*
112                  * cond_broadcast was issued while mutex was held. This means
113                  * that all other waiters have continued, but are contending
114                  * for the mutex at the end of this function because the
115                  * broadcasting thread did not leave cond_broadcast, yet.
116                  * (This is so that it can be sure that each waiter has
117                  * consumed exactly one slice of the semaphor.)
118                  * The last waiter must tell the broadcasting thread that it
119                  * can go on.
120                  */
121                 SetEvent(cond->continue_broadcast);
122                 /*
123                  * Now we go on to contend with all other waiters for
124                  * the mutex. Auf in den Kampf!
125                  */
126         }
127         /* lock external mutex again */
128         EnterCriticalSection(mutex);
129
130         return 0;
131 }
132
133 /*
134  * IMPORTANT: This implementation requires that pthread_cond_signal
135  * is called while the mutex is held that is used in the corresponding
136  * pthread_cond_wait calls!
137  */
138 int pthread_cond_signal(pthread_cond_t *cond)
139 {
140         int have_waiters;
141
142         EnterCriticalSection(&cond->waiters_lock);
143         have_waiters = cond->waiters > 0;
144         LeaveCriticalSection(&cond->waiters_lock);
145
146         /*
147          * Signal only when there are waiters
148          */
149         if (have_waiters)
150                 return ReleaseSemaphore(cond->sema, 1, NULL) ?
151                         0 : err_win_to_posix(GetLastError());
152         else
153                 return 0;
154 }
155
156 /*
157  * DOUBLY IMPORTANT: This implementation requires that pthread_cond_broadcast
158  * is called while the mutex is held that is used in the corresponding
159  * pthread_cond_wait calls!
160  */
161 int pthread_cond_broadcast(pthread_cond_t *cond)
162 {
163         EnterCriticalSection(&cond->waiters_lock);
164
165         if ((cond->was_broadcast = cond->waiters > 0)) {
166                 /* wake up all waiters */
167                 ReleaseSemaphore(cond->sema, cond->waiters, NULL);
168                 LeaveCriticalSection(&cond->waiters_lock);
169                 /*
170                  * At this point all waiters continue. Each one takes its
171                  * slice of the semaphor. Now it's our turn to wait: Since
172                  * the external mutex is held, no thread can leave cond_wait,
173                  * yet. For this reason, we can be sure that no thread gets
174                  * a chance to eat *more* than one slice. OTOH, it means
175                  * that the last waiter must send us a wake-up.
176                  */
177                 WaitForSingleObject(cond->continue_broadcast, INFINITE);
178                 /*
179                  * Since the external mutex is held, no thread can enter
180                  * cond_wait, and, hence, it is safe to reset this flag
181                  * without cond->waiters_lock held.
182                  */
183                 cond->was_broadcast = 0;
184         } else {
185                 LeaveCriticalSection(&cond->waiters_lock);
186         }
187         return 0;
188 }