[vlc-devel] [PATCH 4/4] thread: make vlc_thread_self() always work

[Rémi Denis-Courmont]

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.

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