[vlc-devel] [PATCH 4/4] thread: make vlc_thread_self() always work
Thomas Guillem
thomas at gllm.fr
Tue Feb 18 09:57:43 CET 2020
On Mon, Feb 17, 2020, at 21:56, Rémi Denis-Courmont wrote:
> This changes the return type of vlc_thread_self() to match (one of) the
> C run-time native thread handle type. Then we add a macro to compare
> handles for equality, which may be useful for self-debugging or to
> implement recursive locking.
I am curious, why a project like VLC would want to implement recursive locking ?
I think it's already available on all OS, no ?
It reminds me this MR on libbluray: https://code.videolan.org/videolan/libbluray/merge_requests/17
>
> Without this, vlc_thread_self() returned NULL on non-POSIX platforms
> on threads not created by vlc_clone() - such as the main thread - which
> was not terribly helpful.
>
> This function overlaps with vlc_thread_id(). But unlike the later, it
> works on all platforms. There are in particular no portable ways to
> implement vlc_thread_id() on POSIX Threads.
> ---
> include/vlc_threads.h | 36 ++++++++++++++++++++++++++++--------
> src/android/thread.c | 4 ++--
> src/os2/thread.c | 4 ++--
> src/win32/thread.c | 4 ++--
> 4 files changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/include/vlc_threads.h b/include/vlc_threads.h
> index 647471e517..02f630ae52 100644
> --- a/include/vlc_threads.h
> +++ b/include/vlc_threads.h
> @@ -54,6 +54,10 @@ VLC_API void vlc_testcancel(void);
>
> typedef struct vlc_thread *vlc_thread_t;
> # define VLC_THREAD_CANCELED NULL
> +
> +typedef HANDLE vlc_osthread_t;
> +#define vlc_thread_equal(a,b) ((a) == (b))
> +
> # define LIBVLC_NEED_SLEEP
> typedef struct
> {
> @@ -99,6 +103,10 @@ static inline int vlc_poll(struct pollfd *fds,
> unsigned nfds, int timeout)
>
> typedef struct vlc_thread *vlc_thread_t;
> #define VLC_THREAD_CANCELED NULL
> +
> +typedef unsigned long vlc_osthread_t;
> +#define vlc_thread_equal(a,b) ((a) == (b))
> +
> typedef struct
> {
> bool dynamic;
> @@ -164,6 +172,8 @@ static inline int vlc_poll (struct pollfd *fds,
> unsigned nfds, int timeout)
>
> typedef struct vlc_thread *vlc_thread_t;
> #define VLC_THREAD_CANCELED NULL
> +typedef pthread_t vlc_osthread_t;
> +#define vlc_thread_equal(a,b) pthread_equal(a,b)
> typedef pthread_mutex_t vlc_mutex_t;
> #define VLC_STATIC_MUTEX PTHREAD_MUTEX_INITIALIZER
> typedef pthread_once_t vlc_once_t;
> @@ -209,6 +219,8 @@ static inline int vlc_poll (struct pollfd *fds,
> unsigned nfds, int timeout)
>
> typedef pthread_t vlc_thread_t;
> #define VLC_THREAD_CANCELED PTHREAD_CANCELED
> +typedef pthread_t vlc_osthread_t;
> +#define vlc_thread_equal(a,b) pthread_equal(a,b)
> typedef pthread_mutex_t vlc_mutex_t;
> #define VLC_STATIC_MUTEX PTHREAD_MUTEX_INITIALIZER
> typedef pthread_rwlock_t vlc_rwlock_t;
> @@ -252,6 +264,9 @@ typedef struct
> */
> #define VLC_THREAD_CANCELED PTHREAD_CANCELED
>
> +typedef pthread_t vlc_osthread_t;
> +#define vlc_thread_equal(a,b) pthread_equal(a,b)
> +
> /**
> * Mutex.
> *
> @@ -816,18 +831,21 @@ VLC_API void vlc_control_cancel(vlc_cleanup_t *);
> * Thread handle.
> *
> * This function returns the thread handle of the calling thread.
> + * This works even if the thread was <b>not</b> created with vlc_clone().
> + * As a consequence, depending on the platform, this might or might not be the
> + * same as the @ref vlc_thread_t thread handle returned by vlc_clone().
> *
> - * \note The exact type of the thread handle depends on the platform,
> - * including an integer type, a pointer type or a compound type of any size.
> - * If you need an integer identifier, use vlc_thread_id() instead.
> + * Also depending on the platform, this might be an integer type, a pointer
> + * type, or a compound type of any (reasonable) size. To compare two thread
> + * handles, use the vlc_thread_equal() macro, not a hand-coded comparison.
> + * Comparing the calling thread for equality with another thread is in fact
> + * pretty much the only purpose of this function.
> *
> - * \note vlc_join(vlc_thread_self(), NULL) is undefined,
> - * as it obviously does not make any sense (it might result in a deadlock, but
> - * there are no warranties that it will).
> + * \note If you need an integer identifier, use vlc_thread_id() instead.
> *
> - * \return the thread handle
> + * \return the OS run-time thread handle
> */
> -VLC_API vlc_thread_t vlc_thread_self(void) VLC_USED;
> +VLC_API vlc_osthread_t vlc_thread_self(void) VLC_USED;
>
> /**
> * Thread identifier.
> @@ -841,6 +859,8 @@ VLC_API vlc_thread_t vlc_thread_self(void) VLC_USED;
> * There are no particular semantics to the thread ID with LibVLC.
> * It is provided mainly for tracing and debugging.
> *
> + * See also vlc_thread_self().
> + *
> * \warning This function is not currently implemented on all supported
> * platforms. Where not implemented, it returns (unsigned long)-1.
> *
> diff --git a/src/android/thread.c b/src/android/thread.c
> index d3e8b25c47..da128a769c 100644
> --- a/src/android/thread.c
> +++ b/src/android/thread.c
> @@ -150,9 +150,9 @@ struct vlc_thread
>
> static thread_local struct vlc_thread *thread = NULL;
>
> -vlc_thread_t vlc_thread_self (void)
> +pthread_t vlc_thread_self(void)
> {
> - return thread;
> + return pthread_self();
> }
>
> void vlc_threads_setup (libvlc_int_t *p_libvlc)
> diff --git a/src/os2/thread.c b/src/os2/thread.c
> index f2eb435129..150b916988 100644
> --- a/src/os2/thread.c
> +++ b/src/os2/thread.c
> @@ -674,9 +674,9 @@ int vlc_set_priority (vlc_thread_t th, int priority)
> return VLC_SUCCESS;
> }
>
> -vlc_thread_t vlc_thread_self (void)
> +unsigned long vlc_thread_self(void)
> {
> - return vlc_threadvar_get (thread_key);
> + return vlc_thread_id();
> }
>
> unsigned long vlc_thread_id (void)
> diff --git a/src/win32/thread.c b/src/win32/thread.c
> index e0539f9322..59d55b3925 100644
> --- a/src/win32/thread.c
> +++ b/src/win32/thread.c
> @@ -536,9 +536,9 @@ int vlc_clone_detach (vlc_thread_t *p_handle, void
> *(*entry) (void *),
> return vlc_clone_attr (p_handle, true, entry, data, priority);
> }
>
> -vlc_thread_t vlc_thread_self (void)
> +unsigned long vlc_thread_self(void)
> {
> - return TlsGetValue(thread_key);
> + return GetCurrentThreadId();
> }
>
> unsigned long vlc_thread_id (void)
> --
> 2.25.0
>
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