ref: c311b3b3a9ceb0e45e0d5969bb20f1e95dbd9059
parent: 21173e19994a7ffcbdc321c35c8c8ea8e6219b78
author: John Koleszar <jkoleszar@google.com>
date: Wed Apr 18 12:03:40 EDT 2012
rtcd: serialize function pointer initialization Ensure that RTCD function pointers are set at most once, to silence some data race warnings. Implementation provided for POSIX threads and Win32, with the prior unsynchronized behavior left in place for other platforms. Change-Id: I65c5856df43ef67043b3d5f26ddafddd8fcb2f7e
--- a/vp8/common/generic/systemdependent.c
+++ b/vp8/common/generic/systemdependent.c
@@ -82,6 +82,58 @@
}
#endif
+
+#if HAVE_PTHREAD_H
+#include <pthread.h>
+static void once(void (*func)(void))
+{+ static pthread_once_t lock = PTHREAD_ONCE_INIT;
+ pthread_once(&lock, func);
+}
+
+
+#elif defined(_WIN32)
+static void once(void (*func)(void))
+{+ /* Using a static initializer here rather than InitializeCriticalSection()
+ * since there's no race-free context in which to execute it. Protecting
+ * it with an atomic op like InterlockedCompareExchangePointer introduces
+ * an x86 dependency, and InitOnceExecuteOnce requires Vista.
+ */
+ static CRITICAL_SECTION lock = {(void *)-1, -1, 0, 0, 0, 0};+ static int done;
+
+ EnterCriticalSection(&lock);
+
+ if (!done)
+ {+ func();
+ done = 1;
+ }
+
+ LeaveCriticalSection(&lock);
+}
+
+
+#else
+/* No-op version that performs no synchronization. vpx_rtcd() is idempotent,
+ * so as long as your platform provides atomic loads/stores of pointers
+ * no synchronization is strictly necessary.
+ */
+
+static void once(void (*func)(void))
+{+ static int done;
+
+ if(!done)
+ {+ func();
+ done = 1;
+ }
+}
+#endif
+
+
void vp8_machine_specific_config(VP8_COMMON *ctx)
{#if CONFIG_MULTITHREAD
@@ -94,5 +146,5 @@
ctx->cpu_caps = x86_simd_caps();
#endif
- vpx_rtcd();
+ once(vpx_rtcd);
}