On Tue, 6 Oct 2015 12:41:13 +0200
Hendrik Leppkes <h.lepp...@gmail.com> wrote:
> The emulation uses native InitOnce* APIs on Windows Vista+, and a
> lock-free/allocation-free approach using atomics and spinning for Windows XP.
> ---
> This is in preparation to use pthread_once for global static init functions,
> and eventually removing the global lock in avcodec_open2
>
> compat/w32pthreads.h | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 68 insertions(+)
>
> diff --git a/compat/w32pthreads.h b/compat/w32pthreads.h
> index 3748289..ef28036 100644
> --- a/compat/w32pthreads.h
> +++ b/compat/w32pthreads.h
> @@ -145,6 +145,19 @@ static inline void pthread_cond_signal(pthread_cond_t
> *cond)
> WakeConditionVariable(cond);
> }
>
> +typedef INIT_ONCE pthread_once_t;
> +#define PTHREAD_ONCE_INIT INIT_ONCE_STATIC_INIT
> +
> +static av_unused int pthread_once(pthread_once_t *once_control, void
> (*init_routine)(void))
> +{
> + BOOL pending = FALSE;
> + InitOnceBeginInitialize(once_control, 0, &pending, NULL);
> + if (pending)
> + init_routine();
> + InitOnceComplete(once_control, 0, NULL);
> + return 0;
> +}
> +
> #else // _WIN32_WINNT < 0x0600
> /* for pre-Windows 6.0 platforms we need to define and use our own condition
> * variable and api */
> @@ -291,6 +304,57 @@ static av_unused void pthread_cond_signal(pthread_cond_t
> *cond)
>
> pthread_mutex_unlock(&win32_cond->mtx_broadcast);
> }
> +
> +/* for pre-Windows 6.0 platforms, define INIT_ONCE struct,
> + * compatible to the one used in the native API */
> +
> +typedef union pthread_once_t {
> + void * Ptr; ///< For the Windows 6.0+ native functions
> + LONG state; ///< For the pre-Windows 6.0 compat code
> +} pthread_once_t;
> +
> +#define PTHREAD_ONCE_INIT {0}
> +
> +/* function pointers to init once API on windows 6.0+ kernels */
> +static BOOL (WINAPI *initonce_begin)(pthread_once_t *lpInitOnce, DWORD
> dwFlags, BOOL *fPending, void **lpContext);
> +static BOOL (WINAPI *initonce_complete)(pthread_once_t *lpInitOnce, DWORD
> dwFlags, void *lpContext);
> +
> +static av_unused int pthread_once(pthread_once_t *once_control, void
> (*init_routine)(void))
> +{
> + /* Use native functions on Windows 6.0+ */
> + if (initonce_begin && initonce_complete)
> + {
> + BOOL pending = FALSE;
> + initonce_begin(once_control, 0, &pending, NULL);
> + if (pending)
> + init_routine();
> + initonce_complete(once_control, 0, NULL);
> + return 0;
> + }
> +
> + /* pre-Windows 6.0 compat using a spin-lock */
> + switch (InterlockedCompareExchange(&once_control->state, 1, 0))
> + {
> + /* Initial run */
> + case 0:
> + init_routine();
> + InterlockedExchange(&once_control->state, 2);
> + break;
> + /* Another thread is running init */
> + case 1:
> + while (1) {
> + MemoryBarrier();
> + if (once_control->state == 2)
> + break;
> + Sleep(0);
> + }
> + break;
> + /* Initialization complete */
> + case 2:
> + break;
> + }
> + return 0;
> +}
> #endif
>
> static av_unused void w32thread_init(void)
> @@ -306,6 +370,10 @@ static av_unused void w32thread_init(void)
> (void*)GetProcAddress(kernel_dll, "WakeConditionVariable");
> cond_wait =
> (void*)GetProcAddress(kernel_dll, "SleepConditionVariableCS");
> + initonce_begin =
> + (void*)GetProcAddress(kernel_dll, "InitOnceBeginInitialize");
> + initonce_complete =
> + (void*)GetProcAddress(kernel_dll, "InitOnceComplete");
> #endif
>
> }
Seems all fine to me. (We've essentially did some patch review
iterations on IRC already.)
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