openCV, C++ concurrency, windows - c++

Question

We are building a program that has a server streaming video from a client. We are using C++ in visual studio. Running in debug mode takes away all weird symptoms.
OBS: running in release but turning of optimizations with /0d still gives the symptoms.
Symptoms: While calling imshow("blabla", image); in the server we get the following error: "Unhandled exception at 0x54F26AF8 (opencv_highgui248d.dll) in newCVS2.exe: 0xC0000005: Access violation reading location 0x69577265."
However if we do a imwrite("example.jpg", otherimage); before we do not get this error. image and otherimage are different images. We have tried stepping through the code, no strange jumps are done that I know of.
In the code below search for imwrite("test.jpg",tmp3) with the code below we will get the error, if imwrite is uncommented we will not. I included all the code for reference.
OBS: imwrite solves the problem it is not the cause of it!
thanks in advance, any comments appreciated.
Example of code:
// newCVS2.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#undef UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <process.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#pragma comment (lib, "Ws2_32.lib")
using namespace std;
using namespace cv;
void streamServer(void* arg);
void quit(string msg, int retval);
int connect();
//HANDLE hMutex1;
Mat frame;
Mat img;
SOCKET ListenSocket;
SOCKET ClientSocket;
WSADATA wsaData;
int iResult;
#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "27015"
int iSendResult;
char recvbuf[DEFAULT_BUFLEN];
int recvbuflen = DEFAULT_BUFLEN;
int is_data_ready = 0;
HANDLE hMutex1 = CreateMutex( NULL, FALSE, NULL );
HANDLE syncMutex = CreateMutex( NULL, FALSE, NULL );
void streamServer(void* arg){
int imgSize = img.total()*img.elemSize();
char* sockData = new char[imgSize];
int bytes=0;
int errorMsg = connect();
if(errorMsg != 0){
cout << "error on: " << errorMsg;
}
SYSTEMTIME before;
SYSTEMTIME after;
// Receive until the peer shuts down the connection
memset(sockData, 0x0, sizeof(sockData));
do {
GetSystemTime(&before);
for(int i = 0; i < imgSize; i += iResult){
iResult = recv(ClientSocket, sockData + i, imgSize - i, 0);
if(iResult == -1){
printf("resv failed");
}
}
GetSystemTime(&after);
cout << (((after.wSecond * 1000) + after.wMilliseconds) - ((before.wSecond * 1000 ) + before.wMilliseconds)) << " time for recv \n";
//int ptr = 0;
GetSystemTime(&before);
WaitForSingleObject( hMutex1, INFINITE );
for(int i = 0; i < img.rows; i++){
//row = sockData.part(
for(int j = 0; j < img.cols; j++){
(img.row(i)).col(j) = (uchar)sockData[((img.cols)*i)+j];
//img.at<cv::Vec3b>(i,j) = cv::Vec3b((uchar)sockData[ptr+ 0],(uchar)sockData[ptr+1],(uchar)sockData[ptr+2]);
//ptr = ptr + 3;
}
}
cout << img.rows << " number of rows ";
GetSystemTime(&after);
is_data_ready = 1;
memset(sockData, 0x0, sizeof(sockData));
ReleaseMutex( hMutex1 );
cout << (((after.wSecond * 1000) + after.wMilliseconds) - ((before.wSecond * 1000 ) + before.wMilliseconds)) << " time for annoying shit \n";
if (iResult > 0) {
printf("Bytes received: %d\n", iResult);
}
//Close the connection
else if (iResult == 0)
printf("Connection closing...\n");
//Fail during connection
else {
printf("recv failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
}
} while (iResult > 0);
// shutdown the connection since we're done
iResult = shutdown(ClientSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n", WSAGetLastError());
closesocket(ClientSocket);
WSACleanup();
}
// cleanup
closesocket(ClientSocket);
WSACleanup();
}
int main()
{
int width, height;
width = 640;
height = 480;
img = Mat::zeros( height,width, CV_8UC1);
is_data_ready = 0; // not needed
_beginthread( streamServer, 0, NULL );
//needed to make sure that server does not close
while(true){
WaitForSingleObject( hMutex1, INFINITE );
if(is_data_ready){
cout << img.rows << " number rows before show \n";
cout << img.empty() << " empty? \n";
WaitForSingleObject( syncMutex, INFINITE );
Mat tmp0, tmp1, tmp2, tmp3, tmp4;
tmp4 = img;
bilateralFilter(img, tmp0, -1, 50, 5);
Canny(tmp0, tmp1, 35, 200, 3);
/*imwrite("test.jpg",tmp3);
waitKey(1);*/
ReleaseMutex( syncMutex );
WaitForSingleObject( syncMutex, INFINITE );
imshow("ServerWindow", tmp1);
ReleaseMutex( syncMutex );
waitKey(1);
cout << img.cols << " number cols after show \n";
is_data_ready = 0;
}
ReleaseMutex( hMutex1 );
waitKey(1);
}
//connect();
return 0;
}
void quit(string msg, int retval){
}
int connect(){
/*WSADATA wsaData;
int iResult;
SOCKET ListenSocket = INVALID_SOCKET;
SOCKET ClientSocket = INVALID_SOCKET;
struct addrinfo *result = NULL;
struct addrinfo hints;
int iSendResult;
char recvbuf[DEFAULT_BUFLEN];
int recvbuflen = DEFAULT_BUFLEN;*/
struct addrinfo *result = NULL;
struct addrinfo hints;
ListenSocket = INVALID_SOCKET;
ClientSocket = INVALID_SOCKET;
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed with error: %d\n", iResult);
return 1;
}
ZeroMemory(&hints, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
hints.ai_flags = AI_PASSIVE;
// Resolve the server address and port
iResult = getaddrinfo(NULL, DEFAULT_PORT, &hints, &result);
if ( iResult != 0 ) {
printf("getaddrinfo failed with error: %d\n", iResult);
WSACleanup();
return 1;
}
// Create a SOCKET for connecting to server
ListenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
if (ListenSocket == INVALID_SOCKET) {
printf("socket failed with error: %ld\n", WSAGetLastError());
freeaddrinfo(result);
WSACleanup();
return 1;
}
// Setup the TCP listening socket
iResult = bind( ListenSocket, result->ai_addr, (int)result->ai_addrlen);
if (iResult == SOCKET_ERROR) {
printf("bind failed with error: %d\n", WSAGetLastError());
freeaddrinfo(result);
closesocket(ListenSocket);
WSACleanup();
return 1;
}
freeaddrinfo(result);
iResult = listen(ListenSocket, SOMAXCONN);
if (iResult == SOCKET_ERROR) {
printf("listen failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return 1;
}
// Accept a client socket
ClientSocket = accept(ListenSocket, NULL, NULL);
if (ClientSocket == INVALID_SOCKET) {
printf("accept failed with error: %d\n", WSAGetLastError());
closesocket(ListenSocket);
WSACleanup();
return 1;
}
// No longer need server socket
closesocket(ListenSocket);
return 0;
}
Edit:
If adding the test if tmp1 is empty as suggested I get another exception:
bilateralFilter(img, tmp0, -1, 50, 5);
Canny(tmp0, tmp1, 35, 200, 3);
//ytp = frame;
//testImage = frame;
imwrite("test.jpg",tmp3);
waitKey(1);
waitKey(500);
ReleaseMutex( syncMutex );
WaitForSingleObject( syncMutex, INFINITE );
if (tmp1.empty()) {
std::cout << "tmp1 is empty" << std::endl;
break;
}
imshow("ServerWindow", tmp1);
the program now crashes on imwrite and throws the exception:
Unhandled exception at 0x67BDFF1F (msvcr110d.dll) in newCVS2.exe: 0xC0000005: Access violation reading location 0x67706A2E.
it is making me think that there is some problem accessing the mats

Answer 1

Check if tmp1 is not empty, for example
if (tmp1.empty) {
std::cout << "tmp1 is empty" << std::endl;
break;
}
I noticed that OpenCV's imshow function is not thread-safe (at least on Windows machine). For example, if I call imshow from two different threads my program would crush. The program would also crush if I called namedWindow() command in one thread and then imshow() command in another thread. So make sure you don't do that. As a side note, it is better to create an output window using namedWindow("ServerWindow"), before calling imshow. Create this window only once (outside of the for loop) and in the same thread where you call imshow. This will improve the performance and may fix the issue.

Answer 2

It is because tmp3 is only initialized, it does not have any data. Trying to write tmp0 or tmp1 will work in this code.