Hello, I am using boost condition_variables to block while waiting for an asynchronous response. I am seeing an error that happens at random whenever I am releasing the lock just before calling notify_one. The error goes away if I keep the lock and release after notify_one. Here is the code: class BlockingRequest{ public: // predicate class class ResponseStatus { public: ResponseStatus( bool& received ) : m_received( received ) { } bool operator()() const { return m_received; } private: bool& m_received; }; //blocking request std::string Request( const std::string& request ) { boost::mutex::scoped_lock lock( mutex ); //perform asynchronous request through network or something else, pass RequestHandler as a handler boost::posix_time::milliseconds timeoutDuration( 10000 ); //wait for 10 seconds if( !condition.timed_wait( lock, timeoutDuration, ResponseStatus( received ) ) ) { throw std::exception( "Request timed out" ); } return receivedMessage; } //some other thread calls this function void RequestHandler( const std::string& message, void* caller ) { BlockingRequest* myRequest = reinterpret_cast< BlockingRequest* >( caller ); boost::mutex::scoped_lock lock( myRequest->mutex ); myRequest->receivedMessage = message; myRequest->received = true; /* if this next line in bold is commented out, code works fine... contrary to Boost documentation. http://www.boost.org/doc/libs/1_41_0/doc/html/thread/synchronization.html#th... */ *lock.unlock();* myRequest->condition.notify_one(); } };