vlc_detach: releases a thread handle asynchronously

Note that this can only be used safely in the core. In a plug-in, it
would introduce a race whereby dlclose() unmaps the code segment that
a detached thread is running (this was discussed over a year ago).
For that, we'd need something a bit more involved along the lines of
Win32's FreeLibraryAndExitThread().

src/libvlc.h

@@ -58,6 +58,9 @@ vlc_list_t *vlc_list_find( vlc_object_t *, int, int );
  * Threads subsystem
  */
 
+/* This cannot be used as is from plugins: */
+void vlc_detach (vlc_thread_t);
+
 /* Hopefully, no need to export this. There is a new thread API instead. */
 void vlc_thread_cancel (vlc_object_t *);
 int vlc_object_waitpipe (vlc_object_t *obj);

src/misc/pthread.c

@@ -589,10 +589,10 @@ void vlc_cancel (vlc_thread_t thread_id)
  * occur.
  * @warning
  * A thread cannot join itself (normally VLC will abort if this is attempted).
+ * Also, a detached thread <b>cannot</b> be joined.
  *
  * @param handle thread handle
  * @param p_result [OUT] pointer to write the thread return value or NULL
- * @return 0 on success, a standard error code otherwise.
  */
 void vlc_join (vlc_thread_t handle, void **result)
 {
@@ -600,6 +600,28 @@ void vlc_join (vlc_thread_t handle, void **result)
     VLC_THREAD_ASSERT ("joining thread");
 }
 
+/**
+ * Detaches a thread. When the specified thread completes, it will be
+ * automatically destroyed (in particular, its stack will be reclaimed),
+ * instead of waiting for another thread to call vlc_join(). If the thread has
+ * already completed, it will be destroyed immediately.
+ *
+ * When a thread performs some work asynchronously and may complete much
+ * earlier than it can be joined, detaching the thread can save memory.
+ * However, care must be taken that any resources used by a detached thread
+ * remains valid until the thread completes. This will typically involve some
+ * kind of thread-safe signaling.
+ *
+ * A thread may detach itself.
+ *
+ * @param handle thread handle
+ */
+void vlc_detach (vlc_thread_t handle)
+{
+    int val = pthread_detach (handle);
+    VLC_THREAD_ASSERT ("detaching thread");
+}
+
 /**
  * Save the current cancellation state (enabled or disabled), then disable
  * cancellation for the calling thread.

src/misc/w32thread.c

@@ -497,6 +497,10 @@ void vlc_join (vlc_thread_t handle, void **result)
 #endif
 }
 
+void vlc_detach (vlc_thread_t handle)
+{
+    CloseHandle (handle);
+}
 
 /*** Thread cancellation ***/