1 files changed, 11 insertions, 1 deletions
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index c73b5e09..6d8d8ddd 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -16,13 +16,15 @@
 
 //  Most users requiring mutual exclusion should use Mutex.
 //  SpinLock is provided for use in two situations:
-//   - for use in code that Mutex itself depends on
+//   - for use by Abseil internal code that Mutex itself depends on
 //   - for async signal safety (see below)
 
 // SpinLock is async signal safe.  If a spinlock is used within a signal
 // handler, all code that acquires the lock must ensure that the signal cannot
 // arrive while they are holding the lock.  Typically, this is done by blocking
 // the signal.
+//
+// Threads waiting on a SpinLock may be woken in an arbitrary order.
 
 #ifndef ABSL_BASE_INTERNAL_SPINLOCK_H_
 #define ABSL_BASE_INTERNAL_SPINLOCK_H_
@@ -118,6 +120,14 @@ class ABSL_LOCKABLE SpinLock {
     return (lockword_.load(std::memory_order_relaxed) & kSpinLockHeld) != 0;
   }
 
+  // Return immediately if this thread holds the SpinLock exclusively.
+  // Otherwise, report an error by crashing with a diagnostic.
+  inline void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() {
+    if (!IsHeld()) {
+      ABSL_RAW_LOG(FATAL, "thread should hold the lock on SpinLock");
+    }
+  }
+
  protected:
   // These should not be exported except for testing.