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1 files changed, 47 insertions, 0 deletions

diff --git a/src/rt/sync/spin_lock.cpp b/src/rt/sync/spin_lock.cpp
new file mode 100644
index 00000000000..11a5cb201af
--- /dev/null
+++ b/src/rt/sync/spin_lock.cpp
@@ -0,0 +1,47 @@
+/*
+ * Your average spin lock.
+ */
+
+#include "globals.h"
+
+// #define TRACE
+
+spin_lock::spin_lock() {
+    unlock();
+}
+
+spin_lock::~spin_lock() {
+}
+
+static inline unsigned xchg32(void *ptr, unsigned x) {
+    __asm__ __volatile__("xchgl %0,%1"
+                :"=r" ((unsigned) x)
+                :"m" (*(volatile unsigned *)ptr), "0" (x)
+                :"memory");
+    return x;
+}
+
+void spin_lock::lock() {
+    while (true) {
+        if (!xchg32(&ticket, 1)) {
+            return;
+        }
+        while (ticket) {
+            pause();
+        }
+    }
+#ifdef TRACE
+    printf("  lock: %d", ticket);
+#endif
+}
+
+void spin_lock::unlock() {
+    ticket = 0;
+#ifdef TRACE
+    printf("unlock:");
+#endif
+}
+
+void spin_lock::pause() {
+    asm volatile("pause\n" : : : "memory");
+}