Added SDL_DetachThread() API.

include/SDL_thread.h

@@ -165,13 +165,53 @@ extern DECLSPEC SDL_threadID SDLCALL SDL_GetThreadID(SDL_Thread * thread);
 extern DECLSPEC int SDLCALL SDL_SetThreadPriority(SDL_ThreadPriority priority);
 
 /**
- *  Wait for a thread to finish.
+ *  Wait for a thread to finish. Threads that haven't been detached will
+ *  remain (as a "zombie") until this function cleans them up. Not doing so
+ *  is a resource leak.
+ *
+ *  Once a thread has been cleaned up through this function, the SDL_Thread
+ *  that references it becomes invalid and should not be referenced again.
+ *  As such, only one thread may call SDL_WaitThread() on another.
  *
  *  The return code for the thread function is placed in the area
  *  pointed to by \c status, if \c status is not NULL.
+ *
+ *  You may not wait on a thread that has been used in a call to
+ *  SDL_DetachThread(). Use either that function or this one, but not
+ *  both, or behavior is undefined.
+ *
+ *  It is safe to pass NULL to this function; it is a no-op.
  */
 extern DECLSPEC void SDLCALL SDL_WaitThread(SDL_Thread * thread, int *status);
 
+/**
+ *  A thread may be "detached" to signify that it should not remain until
+ *  another thread has called SDL_WaitThread() on it. Detaching a thread
+ *  is useful for long-running threads that nothing needs to synchronize
+ *  with or further manage. When a detached thread is done, it simply
+ *  goes away.
+ *
+ *  There is no way to recover the return code of a detached thread. If you
+ *  need this, don't detach the thread and instead use SDL_WaitThread().
+ *
+ *  Once a thread is detached, you should usually assume the SDL_Thread isn't
+ *  safe to reference again, as it will become invalid immediately upon
+ *  the detached thread's exit, instead of remaining until someone has called
+ *  SDL_WaitThread() to finally clean it up. As such, don't detach the same
+ *  thread more than once.
+ *
+ *  If a thread has already exited when passed to SDL_DetachThread(), it will
+ *  stop waiting for a call to SDL_WaitThread() and clean up immediately.
+ *  It is not safe to detach a thread that might be used with SDL_WaitThread().
+ *
+ *  You may not call SDL_WaitThread() on a thread that has been detached.
+ *  Use either that function or this one, but not both, or behavior is
+ *  undefined.
+ *
+ *  It is safe to pass NULL to this function; it is a no-op.
+ */
+extern DECLSPEC void SDLCALL SDL_DetachThread(SDL_Thread * thread);
+
 /**
  *  \brief Create an identifier that is globally visible to all threads but refers to data that is thread-specific.
  *

src/thread/SDL_systhread.h

@@ -51,6 +51,9 @@ extern int SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority);
  */
 extern void SDL_SYS_WaitThread(SDL_Thread * thread);
 
+/* Mark thread as cleaned up as soon as it exits, without joining. */
+extern void SDL_SYS_DetachThread(SDL_Thread * thread);
+
 /* Get the thread local storage for this thread */
 extern SDL_TLSData *SDL_SYS_GetTLSData();
 

src/thread/SDL_thread.c

@@ -22,6 +22,7 @@
 
 /* System independent thread management routines for SDL */
 
+#include "SDL_assert.h"
 #include "SDL_thread.h"
 #include "SDL_thread_c.h"
 #include "SDL_systhread.h"
@@ -265,13 +266,14 @@ SDL_RunThread(void *data)
     thread_args *args = (thread_args *) data;
     int (SDLCALL * userfunc) (void *) = args->func;
     void *userdata = args->data;
-    int *statusloc = &args->info->status;
+    SDL_Thread *thread = args->info;
+    int *statusloc = &thread->status;
 
     /* Perform any system-dependent setup - this function may not fail */
-    SDL_SYS_SetupThread(args->info->name);
+    SDL_SYS_SetupThread(thread->name);
 
     /* Get the thread id */
-    args->info->threadid = SDL_ThreadID();
+    thread->threadid = SDL_ThreadID();
 
     /* Wake up the parent thread */
     SDL_SemPost(args->wait);
@@ -281,6 +283,17 @@ SDL_RunThread(void *data)
 
     /* Clean up thread-local storage */
     SDL_TLSCleanup();
+
+    /* Mark us as ready to be joined (or detached) */
+    if (!SDL_AtomicCAS(&thread->state, SDL_THREAD_STATE_ALIVE, SDL_THREAD_STATE_ZOMBIE)) {
+        /* Clean up if something already detached us. */
+        if (SDL_AtomicCAS(&thread->state, SDL_THREAD_STATE_DETACHED, SDL_THREAD_STATE_CLEANED)) {
+            if (thread->name) {
+                SDL_free(thread->name);
+            }
+            SDL_free(thread);
+        }
+    }
 }
 
 #ifdef SDL_PASSED_BEGINTHREAD_ENDTHREAD
@@ -306,8 +319,9 @@ SDL_CreateThread(int (SDLCALL * fn) (void *),
         SDL_OutOfMemory();
         return (NULL);
     }
-    SDL_memset(thread, 0, (sizeof *thread));
+    SDL_zerop(thread);
     thread->status = -1;
+    SDL_AtomicSet(&thread->state, SDL_THREAD_STATE_ALIVE);
 
     /* Set up the arguments for the thread */
     if (name != NULL) {
@@ -410,4 +424,27 @@ SDL_WaitThread(SDL_Thread * thread, int *status)
     }
 }
 
+void
+SDL_DetachThread(SDL_Thread * thread)
+{
+    if (!thread) {
+        return;
+    }
+
+    /* Grab dibs if the state is alive+joinable. */
+    if (SDL_AtomicCAS(&thread->state, SDL_THREAD_STATE_ALIVE, SDL_THREAD_STATE_DETACHED)) {
+        SDL_SYS_DetachThread(thread);
+    } else {
+        /* all other states are pretty final, see where we landed. */
+        const int state = SDL_AtomicGet(&thread->state);
+        if ((state == SDL_THREAD_STATE_DETACHED) || (state == SDL_THREAD_STATE_CLEANED)) {
+            return;  /* already detached (you shouldn't call this twice!) */
+        } else if (state == SDL_THREAD_STATE_ZOMBIE) {
+            SDL_WaitThread(thread, NULL);  /* already done, clean it up. */
+        } else {
+            SDL_assert(0 && "Unexpected thread state");
+        }
+    }
+}
+
 /* vi: set ts=4 sw=4 expandtab: */

src/thread/SDL_thread_c.h

@@ -40,12 +40,21 @@
 #endif
 #include "../SDL_error_c.h"
 
+typedef enum SDL_ThreadState
+{
+    SDL_THREAD_STATE_ALIVE,
+    SDL_THREAD_STATE_DETACHED,
+    SDL_THREAD_STATE_ZOMBIE,
+    SDL_THREAD_STATE_CLEANED,
+} SDL_ThreadState;
+
 /* This is the system-independent thread info structure */
 struct SDL_Thread
 {
     SDL_threadID threadid;
     SYS_ThreadHandle handle;
     int status;
+    SDL_atomic_t state;  /* SDL_THREAD_STATE_* */
     SDL_error errbuf;
     char *name;
     void *data;

src/thread/generic/SDL_systhread.c

@@ -62,4 +62,10 @@ SDL_SYS_WaitThread(SDL_Thread * thread)
     return;
 }
 
+void
+SDL_SYS_DetachThread(SDL_Thread * thread)
+{
+    return;
+}
+
 /* vi: set ts=4 sw=4 expandtab: */

src/thread/psp/SDL_systhread.c

@@ -77,6 +77,12 @@ void SDL_SYS_WaitThread(SDL_Thread *thread)
     sceKernelDeleteThread(thread->handle);
 }
 
+void SDL_SYS_DetachThread(SDL_Thread *thread)
+{
+    /* !!! FIXME: is this correct? */
+    sceKernelDeleteThread(thread->handle);
+}
+
 void SDL_SYS_KillThread(SDL_Thread *thread)
 {
     sceKernelTerminateDeleteThread(thread->handle);

src/thread/pthread/SDL_systhread.c

@@ -213,4 +213,10 @@ SDL_SYS_WaitThread(SDL_Thread * thread)
     pthread_join(thread->handle, 0);
 }
 
+void
+SDL_SYS_DetachThread(SDL_Thread * thread)
+{
+    pthread_detach(thread->handle);
+}
+
 /* vi: set ts=4 sw=4 expandtab: */

src/thread/windows/SDL_systhread.c

@@ -234,6 +234,12 @@ SDL_SYS_WaitThread(SDL_Thread * thread)
     CloseHandle(thread->handle);
 }
 
+void
+SDL_SYS_DetachThread(SDL_Thread * thread)
+{
+    CloseHandle(thread->handle);
+}
+
 #endif /* SDL_THREAD_WINDOWS */
 
 /* vi: set ts=4 sw=4 expandtab: */