qemu-thread-win32.c

   1 /*
   2  * Win32 implementation for mutex/cond/thread functions
   3  *
   4  * Copyright Red Hat, Inc. 2010
   5  *
   6  * Author:
   7  *  Paolo Bonzini <pbonzini@redhat.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  *
  12  */
  13 #include "qemu-common.h"
  14 #include "qemu-thread.h"
  15 #include <process.h>
  16 #include <assert.h>
  17 #include <limits.h>
  18
  19 static void error_exit(int err, const char *msg)
  20 {
  21     char *pstr;
  22
  23     FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
  24                   NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
  25     fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
  26     LocalFree(pstr);
  27     exit(1);
  28 }
  29
  30 void qemu_mutex_init(QemuMutex *mutex)
  31 {
  32     mutex->owner = 0;
  33     InitializeCriticalSection(&mutex->lock);
  34 }
  35
  36 void qemu_mutex_destroy(QemuMutex *mutex)
  37 {
  38     assert(mutex->owner == 0);
  39     DeleteCriticalSection(&mutex->lock);
  40 }
  41
  42 void qemu_mutex_lock(QemuMutex *mutex)
  43 {
  44     EnterCriticalSection(&mutex->lock);
  45
  46     /* Win32 CRITICAL_SECTIONs are recursive.  Assert that we're not
  47      * using them as such.
  48      */
  49     assert(mutex->owner == 0);
  50     mutex->owner = GetCurrentThreadId();
  51 }
  52
  53 int qemu_mutex_trylock(QemuMutex *mutex)
  54 {
  55     int owned;
  56
  57     owned = TryEnterCriticalSection(&mutex->lock);
  58     if (owned) {
  59         assert(mutex->owner == 0);
  60         mutex->owner = GetCurrentThreadId();
  61     }
  62     return !owned;
  63 }
  64
  65 void qemu_mutex_unlock(QemuMutex *mutex)
  66 {
  67     assert(mutex->owner == GetCurrentThreadId());
  68     mutex->owner = 0;
  69     LeaveCriticalSection(&mutex->lock);
  70 }
  71
  72 void qemu_cond_init(QemuCond *cond)
  73 {
  74     memset(cond, 0, sizeof(*cond));
  75
  76     cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
  77     if (!cond->sema) {
  78         error_exit(GetLastError(), __func__);
  79     }
  80     cond->continue_event = CreateEvent(NULL,    /* security */
  81                                        FALSE,   /* auto-reset */
  82                                        FALSE,   /* not signaled */
  83                                        NULL);   /* name */
  84     if (!cond->continue_event) {
  85         error_exit(GetLastError(), __func__);
  86     }
  87 }
  88
  89 void qemu_cond_destroy(QemuCond *cond)
  90 {
  91     BOOL result;
  92     result = CloseHandle(cond->continue_event);
  93     if (!result) {
  94         error_exit(GetLastError(), __func__);
  95     }
  96     cond->continue_event = 0;
  97     result = CloseHandle(cond->sema);
  98     if (!result) {
  99         error_exit(GetLastError(), __func__);
 100     }
 101     cond->sema = 0;
 102 }
 103
 104 void qemu_cond_signal(QemuCond *cond)
 105 {
 106     DWORD result;
 107
 108     /*
 109      * Signal only when there are waiters.  cond->waiters is
 110      * incremented by pthread_cond_wait under the external lock,
 111      * so we are safe about that.
 112      */
 113     if (cond->waiters == 0) {
 114         return;
 115     }
 116
 117     /*
 118      * Waiting threads decrement it outside the external lock, but
 119      * only if another thread is executing pthread_cond_broadcast and
 120      * has the mutex.  So, it also cannot be decremented concurrently
 121      * with this particular access.
 122      */
 123     cond->target = cond->waiters - 1;
 124     result = SignalObjectAndWait(cond->sema, cond->continue_event,
 125                                  INFINITE, FALSE);
 126     if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
 127         error_exit(GetLastError(), __func__);
 128     }
 129 }
 130
 131 void qemu_cond_broadcast(QemuCond *cond)
 132 {
 133     BOOLEAN result;
 134     /*
 135      * As in pthread_cond_signal, access to cond->waiters and
 136      * cond->target is locked via the external mutex.
 137      */
 138     if (cond->waiters == 0) {
 139         return;
 140     }
 141
 142     cond->target = 0;
 143     result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
 144     if (!result) {
 145         error_exit(GetLastError(), __func__);
 146     }
 147
 148     /*
 149      * At this point all waiters continue. Each one takes its
 150      * slice of the semaphore. Now it's our turn to wait: Since
 151      * the external mutex is held, no thread can leave cond_wait,
 152      * yet. For this reason, we can be sure that no thread gets
 153      * a chance to eat *more* than one slice. OTOH, it means
 154      * that the last waiter must send us a wake-up.
 155      */
 156     WaitForSingleObject(cond->continue_event, INFINITE);
 157 }
 158
 159 void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
 160 {
 161     /*
 162      * This access is protected under the mutex.
 163      */
 164     cond->waiters++;
 165
 166     /*
 167      * Unlock external mutex and wait for signal.
 168      * NOTE: we've held mutex locked long enough to increment
 169      * waiters count above, so there's no problem with
 170      * leaving mutex unlocked before we wait on semaphore.
 171      */
 172     qemu_mutex_unlock(mutex);
 173     WaitForSingleObject(cond->sema, INFINITE);
 174
 175     /* Now waiters must rendez-vous with the signaling thread and
 176      * let it continue.  For cond_broadcast this has heavy contention
 177      * and triggers thundering herd.  So goes life.
 178      *
 179      * Decrease waiters count.  The mutex is not taken, so we have
 180      * to do this atomically.
 181      *
 182      * All waiters contend for the mutex at the end of this function
 183      * until the signaling thread relinquishes it.  To ensure
 184      * each waiter consumes exactly one slice of the semaphore,
 185      * the signaling thread stops until it is told by the last
 186      * waiter that it can go on.
 187      */
 188     if (InterlockedDecrement(&cond->waiters) == cond->target) {
 189         SetEvent(cond->continue_event);
 190     }
 191
 192     qemu_mutex_lock(mutex);
 193 }
 194
 195 struct QemuThreadData {
 196     QemuThread *thread;
 197     void *(*start_routine)(void *);
 198     void *arg;
 199 };
 200
 201 static int qemu_thread_tls_index = TLS_OUT_OF_INDEXES;
 202
 203 static unsigned __stdcall win32_start_routine(void *arg)
 204 {
 205     struct QemuThreadData data = *(struct QemuThreadData *) arg;
 206     QemuThread *thread = data.thread;
 207
 208     free(arg);
 209     TlsSetValue(qemu_thread_tls_index, thread);
 210
 211     /*
 212      * Use DuplicateHandle instead of assigning thread->thread in the
 213      * creating thread to avoid races.  It's simpler this way than with
 214      * synchronization.
 215      */
 216     DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
 217                     GetCurrentProcess(), &thread->thread,
 218                     0, FALSE, DUPLICATE_SAME_ACCESS);
 219
 220     qemu_thread_exit(data.start_routine(data.arg));
 221     abort();
 222 }
 223
 224 void qemu_thread_exit(void *arg)
 225 {
 226     QemuThread *thread = TlsGetValue(qemu_thread_tls_index);
 227     thread->ret = arg;
 228     CloseHandle(thread->thread);
 229     thread->thread = NULL;
 230     ExitThread(0);
 231 }
 232
 233 static inline void qemu_thread_init(void)
 234 {
 235     if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
 236         qemu_thread_tls_index = TlsAlloc();
 237         if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
 238             error_exit(ERROR_NO_SYSTEM_RESOURCES, __func__);
 239         }
 240     }
 241 }
 242
 243
 244 void qemu_thread_create(QemuThread *thread,
 245                        void *(*start_routine)(void *),
 246                        void *arg)
 247 {
 248     HANDLE hThread;
 249
 250     struct QemuThreadData *data;
 251     qemu_thread_init();
 252     data = g_malloc(sizeof *data);
 253     data->thread = thread;
 254     data->start_routine = start_routine;
 255     data->arg = arg;
 256
 257     hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
 258                                       data, 0, NULL);
 259     if (!hThread) {
 260         error_exit(GetLastError(), __func__);
 261     }
 262     CloseHandle(hThread);
 263 }
 264
 265 void qemu_thread_get_self(QemuThread *thread)
 266 {
 267     if (!thread->thread) {
 268         /* In the main thread of the process.  Initialize the QemuThread
 269            pointer in TLS, and use the dummy GetCurrentThread handle as
 270            the identifier for qemu_thread_is_self.  */
 271         qemu_thread_init();
 272         TlsSetValue(qemu_thread_tls_index, thread);
 273         thread->thread = GetCurrentThread();
 274     }
 275 }
 276
 277 int qemu_thread_is_self(QemuThread *thread)
 278 {
 279     QemuThread *this_thread = TlsGetValue(qemu_thread_tls_index);
 280     return this_thread->thread == thread->thread;
 281 }