rt: Initialize Windows CRITICAL_SECTION with non-zero spin count

If a CRITICAL_SECTION is not initialized with a spin count, it will
default to 0, even on multi-processor systems. MSDN suggests using
4000. On single-processor systems, the spin count parameter is ignored
and the critical section's spin count defaults to 0.

For Windows >= Vista, extra debug info is allocated for
CRITICAL_SECTIONs but not released in a timely manner. Consider using
InitializeCriticalSectionEx(CRITICAL_SECTION_NO_DEBUG_INFO).

src/rt/sync/lock_and_signal.cpp

@@ -19,7 +19,18 @@ lock_and_signal::lock_and_signal()
     : _holding_thread(INVALID_THREAD)
 {
     _event = CreateEvent(NULL, FALSE, FALSE, NULL);
-    InitializeCriticalSection(&_cs);
+
+    // If a CRITICAL_SECTION is not initialized with a spin count, it will
+    // default to 0, even on multi-processor systems. MSDN suggests using
+    // 4000. On single-processor systems, the spin count parameter is ignored
+    // and the critical section's spin count defaults to 0.
+    const DWORD SPIN_COUNT = 4000;
+    CHECKED(!InitializeCriticalSectionAndSpinCount(&_cs, SPIN_COUNT));
+
+    // TODO? Consider checking GetProcAddress("InitializeCriticalSectionEx")
+    // so Windows >= Vista we can use CRITICAL_SECTION_NO_DEBUG_INFO to avoid
+    // allocating CRITICAL_SECTION debug info that is never released. See:
+    // http://stackoverflow.com/questions/804848/critical-sections-leaking-memory-on-vista-win2008#889853
 }
 
 #else