[NaCl SDK] Support non blocking TCP/UDP

native_client_sdk/src/libraries/sdk_util/auto_lock.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef LIBRARIES_SDK_UTIL_AUTO_LOCK_H_
 #define LIBRARIES_SDK_UTIL_AUTO_LOCK_H_
 
 #include <pthread.h>
 #include "sdk_util/macros.h"
 #include "sdk_util/simple_lock.h"
 
 namespace sdk_util {
 
 // This macro is provided to allow us to quickly instrument locking for
 // debugging purposes.
 #define AUTO_LOCK(lock)                         \
   ::sdk_util::AutoLock Lock##__LINE__(lock);
 
+class AutoUnlock;
+
 class AutoLock {
  public:
   AutoLock(const SimpleLock& lock) {
     lock_ = lock.mutex();
     pthread_mutex_lock(lock_);
   }
 
   ~AutoLock() {
     Unlock();
   }
 
   void Unlock() {
     if (lock_) pthread_mutex_unlock(lock_);
     lock_ = NULL;
   }
 
  private:
   pthread_mutex_t* lock_;
 
+  friend class AutoUnlock;
   DISALLOW_COPY_AND_ASSIGN(AutoLock);
 };
 
+
+class AutoUnlock {
+ public:
+  AutoUnlock() {
+    simple_lock_ = NULL;
+  }
+
+  ~AutoUnlock() {
+    Unlock();
+  }
+
+  void Unlock() {
+    if (simple_lock_)
+      simple_lock_->Unlock();
+
+    simple_lock_ = NULL;
+  }
+
+  void Take(const SimpleLock& lock) {
+    if (simple_lock_ != &lock)
+      Unlock();
+
+    simple_lock_ = &lock;
+  }
+
+  const SimpleLock* Give() {
+    const SimpleLock* out = simple_lock_;
+    simple_lock_ = NULL;
+    return out;
+  }
+
+ private:
+  const SimpleLock* simple_lock_;
+  DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
+};
+
 }  // namespace sdk_util
 
 #endif  // LIBRARIES_SDK_UTIL_AUTO_LOCK_H_