Switch to condition variables

CMakeLists.txt

@@ -4,7 +4,6 @@ project(wepoll)
 include(CMakeParseArguments)
 
 link_libraries(ws2_32)
-link_libraries(synchronization)
 
 if(MSVC)
   add_compile_options(/Wall /WX /wd4127 /wd4191 /wd4201 /wd4242 /wd4710 /wd4711 /wd4820)

src/init.c

@@ -21,7 +21,7 @@ static BOOL CALLBACK init__once_callback(INIT_ONCE* once,
 
   /* N.b. that initialization order matters here. */
   if (ws_global_init() < 0 || nt_global_init() < 0 ||
-      epoll_global_init() < 0)
+      reflock_global_init() < 0 || epoll_global_init() < 0)
     return FALSE;
 
   init__done = true;

src/reflock.c

@@ -14,31 +14,58 @@
 #define REFLOCK__DESTROY_MASK ((long) 0x10000000UL)
 #define REFLOCK__SIGNAL       ((long) 0x20000000UL)
 #define REFLOCK__SIGNAL_MASK  ((long) 0x20000000UL)
-#define REFLOCK__POISON       ((long) 0x300dead0UL)
+#define REFLOCK__AWAIT        ((long) 0x40000000UL)
+#define REFLOCK__AWAIT_MASK   ((long) 0x40000000UL)
+#define REFLOCK__POISON       ((long) 0x800dead0UL)
 /* clang-format on */
 
+static CRITICAL_SECTION signalMutex;
+
+int reflock_global_init(void) {
+  InitializeCriticalSection(&signalMutex);
+  return 0;
+}
+
 void reflock_init(reflock_t* reflock) {
   reflock->state = 0;
+  InitializeConditionVariable(&reflock->cv_signal);
+  InitializeConditionVariable(&reflock->cv_await);
 }
 
 static void reflock__signal_event(reflock_t* reflock) {
-  long state = InterlockedAdd(&reflock->state, REFLOCK__SIGNAL);
-  unused_var(state);
+  BOOL status = TRUE;
 
-  WakeByAddressSingle(reflock);
+  EnterCriticalSection(&signalMutex);
+  long state = InterlockedOr(&reflock->state, REFLOCK__SIGNAL);
+  while ((reflock->state & REFLOCK__AWAIT_MASK) == 0) {
+    status = SleepConditionVariableCS(&reflock->cv_signal, &signalMutex, INFINITE);
+  }
+  LeaveCriticalSection(&signalMutex);
+
+  if (status != TRUE)
+    abort();
+
+  /* At most one reflock__await_event call per reflock. */
+  WakeConditionVariable(&reflock->cv_await);
+  unused_var(state);
 }
 
 static void reflock__await_event(reflock_t* reflock) {
   BOOL status = TRUE;
-  do {
-    status = WaitOnAddress(reflock, reflock, sizeof(reflock_t*), INFINITE);
-  } while ((reflock->state & REFLOCK__SIGNAL_MASK) == 0);
 
-  long state = InterlockedAdd(&reflock->state, -REFLOCK__SIGNAL);
-  unused_var(state);
+  EnterCriticalSection(&signalMutex);
+  long state = InterlockedOr(&reflock->state, REFLOCK__AWAIT);
+  while ((reflock->state & REFLOCK__SIGNAL_MASK) == 0) {
+    status = SleepConditionVariableCS(&reflock->cv_await, &signalMutex, INFINITE);
+  }
+  LeaveCriticalSection(&signalMutex);
 
   if (status != TRUE)
     abort();
+
+  /* Multiple threads could be waiting. */
+  WakeAllConditionVariable(&reflock->cv_signal);
+  unused_var(state);
 }
 
 void reflock_ref(reflock_t* reflock) {
@@ -55,7 +82,8 @@ void reflock_unref(reflock_t* reflock) {
   /* Verify that the lock was referenced and not already destroyed. */
   assert((state & REFLOCK__DESTROY_MASK & ~REFLOCK__DESTROY) == 0);
 
-  if (state == REFLOCK__DESTROY)
+  if ((state & REFLOCK__DESTROY_MASK) == REFLOCK__DESTROY &&
+      (state & REFLOCK__REF_MASK) == 0)
     reflock__signal_event(reflock);
 }
 
@@ -71,5 +99,6 @@ void reflock_unref_and_destroy(reflock_t* reflock) {
     reflock__await_event(reflock);
 
   state = InterlockedExchange(&reflock->state, REFLOCK__POISON);
-  assert(state == REFLOCK__DESTROY);
+  assert((state & REFLOCK__DESTROY_MASK) == REFLOCK__DESTROY);
+  assert((state & REFLOCK__REF_MASK) == 0);
 }

src/reflock.h

@@ -2,6 +2,7 @@
 #define WEPOLL_REFLOCK_H_
 
 #include "config.h"
+#include "win.h"
 
 /* A reflock is a special kind of lock that normally prevents a chunk of
  * memory from being freed, but does allow the chunk of memory to eventually be
@@ -23,8 +24,12 @@
 
 typedef struct reflock {
   volatile long state; /* 32-bit Interlocked APIs operate on `long` values. */
+  CONDITION_VARIABLE cv_signal;
+  CONDITION_VARIABLE cv_await;
 } reflock_t;
 
+WEPOLL_INTERNAL int reflock_global_init(void);
+
 WEPOLL_INTERNAL void reflock_init(reflock_t* reflock);
 WEPOLL_INTERNAL void reflock_ref(reflock_t* reflock);
 WEPOLL_INTERNAL void reflock_unref(reflock_t* reflock);