[Qemu-devel] [PULL 05/15] qemu-thread: add simple test-and-set spinlock

[Richard Henderson <rth@twiddle.net>]

From: Guillaume Delbergue <guillaume.delbergue@greensocs.com>

Reviewed-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Signed-off-by: Guillaume Delbergue <guillaume.delbergue@greensocs.com>
[Rewritten. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Emilio's additions: use TAS instead of atomic_xchg; emit acquire/release
 barriers; return bool from trylock; 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 <cota@braap.org>
Message-Id: <1465412133-3029-6-git-send-email-cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 include/qemu/thread.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index bdae6df..c5d71cf 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -1,6 +1,8 @@
 #ifndef __QEMU_THREAD_H
 #define __QEMU_THREAD_H 1
 
+#include "qemu/processor.h"
+#include "qemu/atomic.h"
 
 typedef struct QemuMutex QemuMutex;
 typedef struct QemuCond QemuCond;
@@ -60,4 +62,37 @@ 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)
+{
+    __sync_lock_release(&spin->value);
+}
+
+static inline void qemu_spin_lock(QemuSpin *spin)
+{
+    while (unlikely(__sync_lock_test_and_set(&spin->value, true))) {
+        while (atomic_read(&spin->value)) {
+            cpu_relax();
+        }
+    }
+}
+
+static inline bool qemu_spin_trylock(QemuSpin *spin)
+{
+    return __sync_lock_test_and_set(&spin->value, true);
+}
+
+static inline bool qemu_spin_locked(QemuSpin *spin)
+{
+    return atomic_read(&spin->value);
+}
+
+static inline void qemu_spin_unlock(QemuSpin *spin)
+{
+    __sync_lock_release(&spin->value);
+}
+
 #endif
-- 
2.5.5