1 files changed, 32 insertions, 2 deletions
diff --git a/base/lock_impl_win.cc b/base/lock_impl_win.cc
index e40db6d..8bb1943 100644
--- a/base/lock_impl_win.cc
+++ b/base/lock_impl_win.cc
@@ -3,8 +3,17 @@
 // found in the LICENSE file.
 
 #include "base/lock_impl.h"
+#include "base/logging.h"
+
+// NOTE: Although windows critical sections support recursive locks, we do not
+// allow this, and we will commonly fire a DCHECK() if a thread attempts to
+// acquire the lock a second time (while already holding it).
 
 LockImpl::LockImpl() {
+#ifndef NDEBUG
+  recursion_count_shadow_ = 0;
+  recursion_used_ = false;
+#endif  // NDEBUG
   // The second parameter is the spin count, for short-held locks it avoid the
   // contending thread from going to sleep which helps performance greatly.
   ::InitializeCriticalSectionAndSpinCount(&os_lock_, 2000);
@@ -15,14 +24,35 @@ LockImpl::~LockImpl() {
 }
 
 bool LockImpl::Try() {
-  return ::TryEnterCriticalSection(&os_lock_) != FALSE;
+  if (::TryEnterCriticalSection(&os_lock_) != FALSE) {
+#ifndef NDEBUG
+    recursion_count_shadow_++;
+    if (2 == recursion_count_shadow_ && !recursion_used_) {
+      recursion_used_ = true;
+      DCHECK(false);  // Catch accidental redundant lock acquisition.
+    }
+#endif
+    return true;
+  }
+  return false;
 }
 
 void LockImpl::Lock() {
   ::EnterCriticalSection(&os_lock_);
+#ifndef NDEBUG
+  // ONLY access data after locking.
+  recursion_count_shadow_++;
+  if (2 == recursion_count_shadow_ && !recursion_used_) {
+    recursion_used_ = true;
+    DCHECK(false);  // Catch accidental redundant lock acquisition.
+  }
+#endif  // NDEBUG
 }
 
 void LockImpl::Unlock() {
+#ifndef NDEBUG
+  --recursion_count_shadow_;  // ONLY access while lock is still held.
+  DCHECK(0 <= recursion_count_shadow_);
+#endif  // NDEBUG
   ::LeaveCriticalSection(&os_lock_);
 }
-