qemu-thread: add QemuEvent
This emulates Win32 manual-reset events using futexes or conditional
variables. Typical ways to use them are with multi-producer,
single-consumer data structures, to test for a complex condition whose
elements come from different threads:
for (;;) {
qemu_event_reset(ev);
... test complex condition ...
if (condition is true) {
break;
}
qemu_event_wait(ev);
}
Or more efficiently (but with some duplication):
... evaluate condition ...
while (!condition) {
qemu_event_reset(ev);
... evaluate condition ...
if (!condition) {
qemu_event_wait(ev);
... evaluate condition ...
}
}
QemuEvent provides a very fast userspace path in the common case when
no other thread is waiting, or the event is not changing state.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 517878d..27a5217 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -227,6 +227,32 @@
}
}
+void qemu_event_init(QemuEvent *ev, bool init)
+{
+ /* Manual reset. */
+ ev->event = CreateEvent(NULL, TRUE, init, NULL);
+}
+
+void qemu_event_destroy(QemuEvent *ev)
+{
+ CloseHandle(ev->event);
+}
+
+void qemu_event_set(QemuEvent *ev)
+{
+ SetEvent(ev->event);
+}
+
+void qemu_event_reset(QemuEvent *ev)
+{
+ ResetEvent(ev->event);
+}
+
+void qemu_event_wait(QemuEvent *ev)
+{
+ WaitForSingleObject(ev->event, INFINITE);
+}
+
struct QemuThreadData {
/* Passed to win32_start_routine. */
void *(*start_routine)(void *);
