1 files changed, 74 insertions, 6 deletions

diff --git a/src/lib/lock/compat_mutex_winthreads.c b/src/lib/lock/compat_mutex_winthreads.c
index 5fe6870a93..8a101e0d25 100644
--- a/src/lib/lock/compat_mutex_winthreads.c
+++ b/src/lib/lock/compat_mutex_winthreads.c
@@ -1,6 +1,6 @@
 /* Copyright (c) 2003-2004, Roger Dingledine
  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
- * Copyright (c) 2007-2020, The Tor Project, Inc. */
+ * Copyright (c) 2007-2021, The Tor Project, Inc. */
 /* See LICENSE for licensing information */
 
 /**
@@ -9,6 +9,23 @@
  * \brief Implement the tor_mutex API using CRITICAL_SECTION.
  **/
 
+#include "orconfig.h"
+
+/* For SRW locks support */
+#ifndef WINVER
+#error "orconfig.h didn't define WINVER"
+#endif
+#ifndef _WIN32_WINNT
+#error "orconfig.h didn't define _WIN32_WINNT"
+#endif
+#if WINVER < 0x0600
+#error "winver too low"
+#endif
+#if _WIN32_WINNT < 0x0600
+#error "winver too low"
+#endif
+
+#include <windows.h>
 #include "lib/lock/compat_mutex.h"
 #include "lib/err/torerr.h"
 
@@ -20,27 +37,78 @@ tor_locking_init(void)
 void
 tor_mutex_init(tor_mutex_t *m)
 {
-  InitializeCriticalSection(&m->mutex);
+  m->type = RECURSIVE;
+  m->lock_owner = 0;
+  m->lock_count = 0;
+  InitializeSRWLock(&m->mutex);
 }
 void
 tor_mutex_init_nonrecursive(tor_mutex_t *m)
 {
-  InitializeCriticalSection(&m->mutex);
+  m->type = NON_RECURSIVE;
+  InitializeSRWLock(&m->mutex);
 }
 
 void
 tor_mutex_uninit(tor_mutex_t *m)
 {
-  DeleteCriticalSection(&m->mutex);
+  (void) m;
+}
+
+static void
+tor_mutex_acquire_recursive(tor_mutex_t *m)
+{
+  LONG thread_id = GetCurrentThreadId();
+  // use InterlockedCompareExchange to perform an atomic read
+  LONG lock_owner = InterlockedCompareExchange(&m->lock_owner, 0, 0);
+  if (thread_id == lock_owner) {
+    ++m->lock_count;
+    return;
+  }
+  AcquireSRWLockExclusive(&m->mutex);
+  InterlockedExchange(&m->lock_owner, thread_id);
+  m->lock_count = 1;
+}
+
+static void
+tor_mutex_acquire_nonrecursive(tor_mutex_t *m)
+{
+  AcquireSRWLockExclusive(&m->mutex);
 }
+
 void
 tor_mutex_acquire(tor_mutex_t *m)
 {
   raw_assert(m);
-  EnterCriticalSection(&m->mutex);
+  if (m->type == NON_RECURSIVE) {
+    tor_mutex_acquire_nonrecursive(m);
+  } else {
+    tor_mutex_acquire_recursive(m);
+  }
+}
+
+static void
+tor_mutex_release_recursive(tor_mutex_t *m)
+{
+  if (--m->lock_count) {
+    return;
+  }
+  InterlockedExchange(&m->lock_owner, 0);
+  ReleaseSRWLockExclusive(&m->mutex);
 }
+
+static void
+tor_mutex_release_nonrecursive(tor_mutex_t *m)
+{
+  ReleaseSRWLockExclusive(&m->mutex);
+}
+
 void
 tor_mutex_release(tor_mutex_t *m)
 {
-  LeaveCriticalSection(&m->mutex);
+  if (m->type == NON_RECURSIVE) {
+    tor_mutex_release_nonrecursive(m);
+  } else {
+    tor_mutex_release_recursive(m);
+  }
 }