5 files changed, 62 insertions, 20 deletions
diff --git a/include/qemu/futex.h b/include/qemu/futex.h
index 91ae88966e..607613eec8 100644
--- a/include/qemu/futex.h
+++ b/include/qemu/futex.h
@@ -1,5 +1,5 @@
 /*
- * Wrappers around Linux futex syscall
+ * Wrappers around Linux futex syscall and similar
  *
  * Copyright Red Hat, Inc. 2017
  *
@@ -11,17 +11,35 @@
  *
  */
 
+/*
+ * Note that a wake-up can also be caused by common futex usage patterns in
+ * unrelated code that happened to have previously used the futex word's
+ * memory location (e.g., typical futex-based implementations of Pthreads
+ * mutexes can cause this under some conditions).  Therefore, qemu_futex_wait()
+ * callers should always conservatively assume that it is a spurious wake-up,
+ * and use the futex word's value (i.e., the user-space synchronization scheme)
+ * to decide whether to continue to block or not.
+ */
+
 #ifndef QEMU_FUTEX_H
 #define QEMU_FUTEX_H
 
+#define HAVE_FUTEX
+
+#ifdef CONFIG_LINUX
 #include <sys/syscall.h>
 #include <linux/futex.h>
 
 #define qemu_futex(...)              syscall(__NR_futex, __VA_ARGS__)
 
-static inline void qemu_futex_wake(void *f, int n)
+static inline void qemu_futex_wake_all(void *f)
 {
-    qemu_futex(f, FUTEX_WAKE, n, NULL, NULL, 0);
+    qemu_futex(f, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
+}
+
+static inline void qemu_futex_wake_single(void *f)
+{
+    qemu_futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
 }
 
 static inline void qemu_futex_wait(void *f, unsigned val)
@@ -37,5 +55,25 @@ static inline void qemu_futex_wait(void *f, unsigned val)
         }
     }
 }
+#elif defined(CONFIG_WIN32)
+#include <synchapi.h>
+
+static inline void qemu_futex_wake_all(void *f)
+{
+    WakeByAddressAll(f);
+}
+
+static inline void qemu_futex_wake_single(void *f)
+{
+    WakeByAddressSingle(f);
+}
+
+static inline void qemu_futex_wait(void *f, unsigned val)
+{
+    WaitOnAddress(f, &val, sizeof(val), INFINITE);
+}
+#else
+#undef HAVE_FUTEX
+#endif
 
 #endif /* QEMU_FUTEX_H */
diff --git a/include/qemu/lockcnt.h b/include/qemu/lockcnt.h
index f4b62a3f70..5a2800e3f1 100644
--- a/include/qemu/lockcnt.h
+++ b/include/qemu/lockcnt.h
@@ -17,7 +17,7 @@
 typedef struct QemuLockCnt QemuLockCnt;
 
 struct QemuLockCnt {
-#ifndef CONFIG_LINUX
+#ifndef HAVE_FUTEX
     QemuMutex mutex;
 #endif
     unsigned count;
diff --git a/include/qemu/thread-posix.h b/include/qemu/thread-posix.h
index 5f2f3d1386..758808b705 100644
--- a/include/qemu/thread-posix.h
+++ b/include/qemu/thread-posix.h
@@ -32,15 +32,6 @@ struct QemuSemaphore {
     unsigned int count;
 };
 
-struct QemuEvent {
-#ifndef __linux__
-    pthread_mutex_t lock;
-    pthread_cond_t cond;
-#endif
-    unsigned value;
-    bool initialized;
-};
-
 struct QemuThread {
     pthread_t thread;
 };
diff --git a/include/qemu/thread-win32.h b/include/qemu/thread-win32.h
index d95af4498f..da9e732299 100644
--- a/include/qemu/thread-win32.h
+++ b/include/qemu/thread-win32.h
@@ -28,12 +28,6 @@ struct QemuSemaphore {
     bool initialized;
 };
 
-struct QemuEvent {
-    int value;
-    HANDLE event;
-    bool initialized;
-};
-
 typedef struct QemuThreadData QemuThreadData;
 struct QemuThread {
     QemuThreadData *data;
diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index 6f800aad31..f0302ed01f 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -3,13 +3,32 @@
 
 #include "qemu/processor.h"
 #include "qemu/atomic.h"
+#include "qemu/futex.h"
 
 typedef struct QemuCond QemuCond;
 typedef struct QemuSemaphore QemuSemaphore;
-typedef struct QemuEvent QemuEvent;
 typedef struct QemuLockCnt QemuLockCnt;
 typedef struct QemuThread QemuThread;
 
+/*
+ * QemuEvent
+ * =========
+ *
+ * QemuEvent is an implementation of Win32 manual-reset event object.
+ * For details, refer to:
+ * https://learn.microsoft.com/en-us/windows/win32/sync/using-event-objects
+ *
+ * QemuEvent is more lightweight than QemuSemaphore when HAVE_FUTEX is defined.
+ */
+typedef struct QemuEvent {
+#ifndef HAVE_FUTEX
+    pthread_mutex_t lock;
+    pthread_cond_t cond;
+#endif
+    unsigned value;
+    bool initialized;
+} QemuEvent;
+
 #ifdef _WIN32
 #include "qemu/thread-win32.h"
 #else