stream: separate posix/win32 cancellation code

This code evolved into an ifdef mess as support for cancellation on
Windows was added. Make the Windows-specific code completely separate.
It looks cleaner, and it also means that some of the posix code is not
uselessly enabled on Windows. The latter made msvcrt.dll output warnings
because it does not like -1 passed as FD to read/write. (The same would
be harmless on POSIX.)

stream/stream.c

@@ -952,20 +952,15 @@ struct bstr stream_read_file(const char *filename, void *talloc_ctx,
     return res;
 }
 
+#ifndef __MINGW32__
 struct mp_cancel {
     atomic_bool triggered;
-#ifdef __MINGW32__
-    HANDLE event;
-#endif
     int wakeup_pipe[2];
 };
 
 static void cancel_destroy(void *p)
 {
     struct mp_cancel *c = p;
-#ifdef __MINGW32__
-    CloseHandle(c->event);
-#endif
     close(c->wakeup_pipe[0]);
     close(c->wakeup_pipe[1]);
 }
@@ -975,9 +970,6 @@ struct mp_cancel *mp_cancel_new(void *talloc_ctx)
     struct mp_cancel *c = talloc_ptrtype(talloc_ctx, c);
     talloc_set_destructor(c, cancel_destroy);
     *c = (struct mp_cancel){.triggered = ATOMIC_VAR_INIT(false)};
-#ifdef __MINGW32__
-    c->event = CreateEventW(NULL, TRUE, FALSE, NULL);
-#endif
     mp_make_wakeup_pipe(c->wakeup_pipe);
     return c;
 }
@@ -986,9 +978,6 @@ struct mp_cancel *mp_cancel_new(void *talloc_ctx)
 void mp_cancel_trigger(struct mp_cancel *c)
 {
     atomic_store(&c->triggered, true);
-#ifdef __MINGW32__
-    SetEvent(c->event);
-#endif
     write(c->wakeup_pipe[1], &(char){0}, 1);
 }
 
@@ -996,9 +985,6 @@ void mp_cancel_trigger(struct mp_cancel *c)
 void mp_cancel_reset(struct mp_cancel *c)
 {
     atomic_store(&c->triggered, false);
-#ifdef __MINGW32__
-    ResetEvent(c->event);
-#endif
     // Flush it fully.
     while (1) {
         int r = read(c->wakeup_pipe[0], &(char[256]){0}, 256);
@@ -1018,27 +1004,12 @@ bool mp_cancel_test(struct mp_cancel *c)
 
 // Wait until the even is signaled. If the timeout (in seconds) expires, return
 // false. timeout==0 polls, timeout<0 waits forever.
-#ifdef __MINGW32__
-bool mp_cancel_wait(struct mp_cancel *c, double timeout)
-{
-    return WaitForSingleObject(c->event, timeout < 0 ? INFINITE : timeout * 1000)
-            == WAIT_OBJECT_0;
-}
-#else
 bool mp_cancel_wait(struct mp_cancel *c, double timeout)
 {
     struct pollfd fd = { .fd = c->wakeup_pipe[0], .events = POLLIN };
     poll(&fd, 1, timeout * 1000);
     return fd.revents & POLLIN;
 }
-#endif
-
-#ifdef __MINGW32__
-void *mp_cancel_get_event(struct mp_cancel *c)
-{
-    return c->event;
-}
-#endif
 
 // The FD becomes readable if mp_cancel_test() would return true.
 // Don't actually read from it, just use it for poll().
@@ -1047,6 +1018,63 @@ int mp_cancel_get_fd(struct mp_cancel *c)
     return c->wakeup_pipe[0];
 }
 
+#else
+
+struct mp_cancel {
+    atomic_bool triggered;
+    HANDLE event;
+};
+
+static void cancel_destroy(void *p)
+{
+    struct mp_cancel *c = p;
+    CloseHandle(c->event);
+}
+
+struct mp_cancel *mp_cancel_new(void *talloc_ctx)
+{
+    struct mp_cancel *c = talloc_ptrtype(talloc_ctx, c);
+    talloc_set_destructor(c, cancel_destroy);
+    *c = (struct mp_cancel){.triggered = ATOMIC_VAR_INIT(false)};
+    c->event = CreateEventW(NULL, TRUE, FALSE, NULL);
+    return c;
+}
+
+void mp_cancel_trigger(struct mp_cancel *c)
+{
+    atomic_store(&c->triggered, true);
+    SetEvent(c->event);
+}
+
+void mp_cancel_reset(struct mp_cancel *c)
+{
+    atomic_store(&c->triggered, false);
+    ResetEvent(c->event);
+}
+
+bool mp_cancel_test(struct mp_cancel *c)
+{
+    return c ? atomic_load_explicit(&c->triggered, memory_order_relaxed) : false;
+}
+
+bool mp_cancel_wait(struct mp_cancel *c, double timeout)
+{
+    return WaitForSingleObject(c->event, timeout < 0 ? INFINITE : timeout * 1000)
+            == WAIT_OBJECT_0;
+}
+
+void *mp_cancel_get_event(struct mp_cancel *c)
+{
+    return c->event;
+}
+
+int mp_cancel_get_fd(struct mp_cancel *c)
+{
+    return -1;
+}
+
+#endif
+
 char **stream_get_proto_list(void)
 {
     char **list = NULL;