How can I use appropriate the lock mutex function, for three threads in C++? - c++

Question

I have a question about threads but I think that is difficult to explain, so be patient.
I have two pthreads in a QT/C++ program and one signal, Signal fills a buffer, One thread copies the buffer and one to process the buffer's data.
fill buffer1 ----Copy buffer1 to buffer2----process the buffer's 2 data
Signal's function:
void MainWindow::TcpData()
{
if(socket->bytesAvailable()>(DATA_LEN)) {
QByteArray array = socket ->readAll();
if(pthread_mutex_trylock(&data_mutex)==0)
{
if((p+array.size())<(MAX_TCP_BUFFER_SIZE+100))
{
memcpy(BUFFER+p,array.data(),array.size());
p+=array.size();
}
else {
p=0;
memcpy(BUFFER,array.data(),array.size());
p+=array.size();
}
pthread_mutex_unlock(&data_mutex);
}
}
}
Thread 1:
void *MainWindow::copyTCPdata() {
pthread_mutex_lock(&data_mutex);
while(1) {
if(data_ready) {
pthread_cond_wait(&data_cond,&data_mutex);
continue;
}
/* Move the last part of the previous buffer, that was not processed,
* on the start of the new buffer. */
memcpy(data, data+DATA_LEN, (FULL_LEN-1)*4);
/* Read the new data. */
memcpy(data+(FULL_LEN-1)*4, BUFFER,DATA_LEN);
memcpy(BUFFER,BUFFER+DATA_LEN,p);
if(p>DATA_LEN) p=p-DATA_LEN;
data_ready = 1;
pthread_cond_signal(&data_cond);
pthread_mutex_unlock(&data_mutex);
} }
Thread 2:
void *MainWindow::processData {
while(1) {
if(!data_ready) {
pthread_cond_wait(&data_cond,&data_mutex);
continue;
}
data_ready = 0;
pthread_cond_signal(&data_cond);
pthread_mutex_unlock(&data_mutex);
detectSignal(data);
pthread_mutex_lock(&data_mutex);
}
}
I think am loosing data with this way, but the program is more stable, Can someone suggest me a better solution?