1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/media/libvpx/vpx_ports/vpx_once.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,102 @@
1.4 +/*
1.5 + * Copyright (c) 2011 The WebM project authors. All Rights Reserved.
1.6 + *
1.7 + * Use of this source code is governed by a BSD-style license
1.8 + * that can be found in the LICENSE file in the root of the source
1.9 + * tree. An additional intellectual property rights grant can be found
1.10 + * in the file PATENTS. All contributing project authors may
1.11 + * be found in the AUTHORS file in the root of the source tree.
1.12 + */
1.13 +#ifndef VPX_ONCE_H
1.14 +#define VPX_ONCE_H
1.15 +
1.16 +#include "vpx_config.h"
1.17 +
1.18 +#if CONFIG_MULTITHREAD && defined(_WIN32)
1.19 +#include <windows.h>
1.20 +#include <stdlib.h>
1.21 +static void once(void (*func)(void))
1.22 +{
1.23 + static CRITICAL_SECTION *lock;
1.24 + static LONG waiters;
1.25 + static int done;
1.26 + void *lock_ptr = &lock;
1.27 +
1.28 + /* If the initialization is complete, return early. This isn't just an
1.29 + * optimization, it prevents races on the destruction of the global
1.30 + * lock.
1.31 + */
1.32 + if(done)
1.33 + return;
1.34 +
1.35 + InterlockedIncrement(&waiters);
1.36 +
1.37 + /* Get a lock. We create one and try to make it the one-true-lock,
1.38 + * throwing it away if we lost the race.
1.39 + */
1.40 +
1.41 + {
1.42 + /* Scope to protect access to new_lock */
1.43 + CRITICAL_SECTION *new_lock = malloc(sizeof(CRITICAL_SECTION));
1.44 + InitializeCriticalSection(new_lock);
1.45 + if (InterlockedCompareExchangePointer(lock_ptr, new_lock, NULL) != NULL)
1.46 + {
1.47 + DeleteCriticalSection(new_lock);
1.48 + free(new_lock);
1.49 + }
1.50 + }
1.51 +
1.52 + /* At this point, we have a lock that can be synchronized on. We don't
1.53 + * care which thread actually performed the allocation.
1.54 + */
1.55 +
1.56 + EnterCriticalSection(lock);
1.57 +
1.58 + if (!done)
1.59 + {
1.60 + func();
1.61 + done = 1;
1.62 + }
1.63 +
1.64 + LeaveCriticalSection(lock);
1.65 +
1.66 + /* Last one out should free resources. The destructed objects are
1.67 + * protected by checking if(done) above.
1.68 + */
1.69 + if(!InterlockedDecrement(&waiters))
1.70 + {
1.71 + DeleteCriticalSection(lock);
1.72 + free(lock);
1.73 + lock = NULL;
1.74 + }
1.75 +}
1.76 +
1.77 +
1.78 +#elif CONFIG_MULTITHREAD && HAVE_PTHREAD_H
1.79 +#include <pthread.h>
1.80 +static void once(void (*func)(void))
1.81 +{
1.82 + static pthread_once_t lock = PTHREAD_ONCE_INIT;
1.83 + pthread_once(&lock, func);
1.84 +}
1.85 +
1.86 +
1.87 +#else
1.88 +/* No-op version that performs no synchronization. vp8_rtcd() is idempotent,
1.89 + * so as long as your platform provides atomic loads/stores of pointers
1.90 + * no synchronization is strictly necessary.
1.91 + */
1.92 +
1.93 +static void once(void (*func)(void))
1.94 +{
1.95 + static int done;
1.96 +
1.97 + if(!done)
1.98 + {
1.99 + func();
1.100 + done = 1;
1.101 + }
1.102 +}
1.103 +#endif
1.104 +
1.105 +#endif
