[Qemu-devel] [PATCH v5 07/18] qemu-thread: add simple test-and-set spinlock

[Emilio G. Cota]

From: Guillaume Delbergue <address@hidden>

Signed-off-by: Guillaume Delbergue <address@hidden>
[Rewritten. - Paolo]
Signed-off-by: Paolo Bonzini <address@hidden>
[Emilio's additions: use TAS instead of atomic_xchg; emit acquire/release
 barriers; call cpu_relax() while spinning; optimize for uncontended locks by
 acquiring the lock with TAS instead of TATAS; add qemu_spin_locked().]
Signed-off-by: Emilio G. Cota <address@hidden>
---
 include/qemu/thread.h | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index bdae6df..4b74ee5 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -1,6 +1,9 @@
 #ifndef __QEMU_THREAD_H
 #define __QEMU_THREAD_H 1
 
+#include <errno.h>
+#include "qemu/processor.h"
+#include "qemu/atomic.h"
 
 typedef struct QemuMutex QemuMutex;
 typedef struct QemuCond QemuCond;
@@ -60,4 +63,40 @@ struct Notifier;
 void qemu_thread_atexit_add(struct Notifier *notifier);
 void qemu_thread_atexit_remove(struct Notifier *notifier);
 
+typedef struct QemuSpin {
+    int value;
+} QemuSpin;
+
+static inline void qemu_spin_init(QemuSpin *spin)
+{
+    atomic_set_release(&spin->value, 0);
+}
+
+static inline void qemu_spin_lock(QemuSpin *spin)
+{
+    while (atomic_test_and_set_acquire(&spin->value)) {
+        while (atomic_read(&spin->value)) {
+            cpu_relax();
+        }
+    }
+}
+
+static inline int qemu_spin_trylock(QemuSpin *spin)
+{
+    if (atomic_test_and_set_acquire(&spin->value)) {
+        return -EBUSY;
+    }
+    return 0;
+}
+
+static inline bool qemu_spin_locked(QemuSpin *spin)
+{
+    return atomic_read_acquire(&spin->value);
+}
+
+static inline void qemu_spin_unlock(QemuSpin *spin)
+{
+    atomic_set_release(&spin->value, 0);
+}
+
 #endif
-- 
2.5.0