SRWLocks FTW!

Modern Windows (Vista and later) have light weight Slim Read/Write locks
which only occupy 64 bits, and don't require any memory allocation to
create.

While here clean up a few more unreferenced variables found with the
Microsoft compilers.

3 files changed, 17 insertions, 27 deletions

diff --git a/src/platform/windows/win_debug.c b/src/platform/windows/win_debug.c
index a4edef0d..43db0505 100644
--- a/src/platform/windows/win_debug.c
+++ b/src/platform/windows/win_debug.c
@@ -77,6 +77,7 @@ nni_plat_errno(int errnum)
 	return (NNG_ESYSERR + errnum);
 }
 
+
 // Windows has infinite numbers of error codes it seems.  We only bother
 // with the ones that are relevant to us (we think).  Note that there is
 // no overlap between errnos and GetLastError values.
diff --git a/src/platform/windows/win_impl.h b/src/platform/windows/win_impl.h
index 85f73bf7..fd8f3f79 100644
--- a/src/platform/windows/win_impl.h
+++ b/src/platform/windows/win_impl.h
@@ -26,7 +26,7 @@
 // These types are provided for here, to permit them to be directly inlined
 // elsewhere.
 
-typedef struct nni_win_event nni_win_event;
+typedef struct nni_win_event   nni_win_event;
 
 // nni_win_event is used with io completion ports.  This allows us to get
 // to a specific completion callback without requiring the poller (in the
@@ -60,14 +60,14 @@ struct nni_plat_thr {
 };
 
 struct nni_plat_mtx {
-	CRITICAL_SECTION	cs;
-	DWORD			owner;
-	int			init;
+	SRWLOCK srl;
+	DWORD	owner;
+	int	init;
 };
 
 struct nni_plat_cv {
 	CONDITION_VARIABLE	cv;
-	CRITICAL_SECTION *	cs;
+	PSRWLOCK		srl;
 };
 
 extern int nni_win_error(int);
diff --git a/src/platform/windows/win_thread.c b/src/platform/windows/win_thread.c
index be94d638..f3103079 100644
--- a/src/platform/windows/win_thread.c
+++ b/src/platform/windows/win_thread.c
@@ -34,7 +34,7 @@ nni_free(void *b, size_t z)
 int
 nni_plat_mtx_init(nni_plat_mtx *mtx)
 {
-	InitializeCriticalSection(&mtx->cs);
+	InitializeSRWLock(&mtx->srl);
 	mtx->init = 1;
 	return (0);
 }
@@ -43,24 +43,21 @@ nni_plat_mtx_init(nni_plat_mtx *mtx)
 void
 nni_plat_mtx_fini(nni_plat_mtx *mtx)
 {
-	if (mtx->init) {
-		DeleteCriticalSection(&mtx->cs);
-		mtx->init = 0;
-	}
+	mtx->init = 0;
 }
 
 
 void
 nni_plat_mtx_lock(nni_plat_mtx *mtx)
 {
-	EnterCriticalSection(&mtx->cs);
+	AcquireSRWLockExclusive(&mtx->srl);
 }
 
 
 void
 nni_plat_mtx_unlock(nni_plat_mtx *mtx)
 {
-	LeaveCriticalSection(&mtx->cs);
+	ReleaseSRWLockExclusive(&mtx->srl);
 }
 
 
@@ -68,7 +65,7 @@ int
 nni_plat_cv_init(nni_plat_cv *cv, nni_plat_mtx *mtx)
 {
 	InitializeConditionVariable(&cv->cv);
-	cv->cs = &mtx->cs;
+	cv->srl = &mtx->srl;
 	return (0);
 }
 
@@ -83,7 +80,7 @@ nni_plat_cv_wake(nni_plat_cv *cv)
 void
 nni_plat_cv_wait(nni_plat_cv *cv)
 {
-	(void) SleepConditionVariableCS(&cv->cv, cv->cs, INFINITE);
+	(void) SleepConditionVariableSRW(&cv->cv, cv->srl, INFINITE, 0);
 }
 
 
@@ -102,7 +99,7 @@ nni_plat_cv_until(nni_plat_cv *cv, nni_time until)
 		msec = (DWORD) (((until - now) + 999)/1000);
 	}
 
-	ok = SleepConditionVariableCS(&cv->cv, cv->cs, msec);
+	ok = SleepConditionVariableSRW(&cv->cv, cv->srl, msec, 0);
 	return (ok ? 0 : NNG_ETIMEDOUT);
 }
 
@@ -156,23 +153,16 @@ nni_plat_thr_fini(nni_plat_thr *thr)
 int
 nni_plat_init(int (*helper)(void))
 {
-	LONG old;
-	static LONG initing = 0;
 	static LONG inited = 0;
 	int rv;
+	static SRWLOCK lock = SRWLOCK_INIT;
 
 	if (inited) {
 		return (0);     // fast path
 	}
 
-	// This logic gets us to initialize the platform just once.
-	// If two threads enter here together, only one will get to run,
-	// and the other will be put to sleep briefly so that the first
-	// can complete.  This is a poor man's singleton initializer, since
-	// we can't statically initialize critical sections.
-	while ((old = InterlockedCompareExchange(&initing, 0, 1)) != 0) {
-		Sleep(1);
-	}
+	AcquireSRWLockExclusive(&lock);
+
 	if (!inited) {
 		WSADATA data;
 		WORD ver;
@@ -185,7 +175,6 @@ nni_plat_init(int (*helper)(void))
 			rv = NNG_EINVAL;
 			goto out;
 		}
-		printf("STARTING...\n");
 		if ((rv = nni_win_iocp_sysinit()) != 0) {
 			goto out;
 		}
@@ -197,7 +186,7 @@ nni_plat_init(int (*helper)(void))
 	}
 
 out:
-	InterlockedExchange(&initing, 0);
+	ReleaseSRWLockExclusive(&lock);
 
 	return (rv);
 }