TCP Server

D300

Hey,
i´m putting together a tcp server and I´m wondering what causes the mode switches and underruns on the audio thread.

help appreciated 🙂

#include <Bela.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string.h>

#define PORT 8888
#define MAX_CONNECTIONS 5
#define BUFFER_SIZE 1024

int server_fd;
int client_socket;
char buffer[BUFFER_SIZE] = {0};
char *response = "Hello from BELA Server!";

AuxiliaryTask receiveTask;
int receiveTaskPriority = 50;

void receiveDataTask(void*)
{
    while(!Bela_stopRequested())
	{
	    // Receive data from the client
	    int valread = recv(client_socket, buffer, BUFFER_SIZE, 0);
	    if (valread > 0) 
	    {
	        rt_printf("Received: %s\n", buffer);
	
	        // Send response to the client
	        send(client_socket, response, strlen(response), 0);
	        rt_printf("Response sent.\n");
	        
	        // Close the client socket
    		close(client_socket);
	    }
	    else 
	    {
			// no data to read right now. Briefly sleep and try again
			usleep(10000);
		}
	}
}

bool setup(BelaContext *context, void *userData)
{
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);

    // Create socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        rt_printf("socket failed\n");
        return false;
    }

    // Set socket options
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        rt_printf("setsockopt failed\n");
        return false;
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Bind socket to the specified address and port
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        rt_printf("bind failed\n");
        return false;
    }

    // Start listening for incoming connections
    if (listen(server_fd, MAX_CONNECTIONS) < 0) {
        rt_printf("listen failed\n");
        return false;
    }

    rt_printf("Server listening on port %d...\n", PORT);

    // Create auxiliary task for receiving data
    receiveTask = Bela_createAuxiliaryTask(&receiveDataTask, receiveTaskPriority, "receiveTask", NULL);

    return true;
}

void render(BelaContext *context, void *userData)
{
    // Accept new connections
    if ((client_socket = accept(server_fd, NULL, NULL)) < 0) {
        //rt_printf("accept failed\n");
        return;
    }

    // Schedule the auxiliary task to receive data
    Bela_scheduleAuxiliaryTask(receiveTask);
}

void cleanup(BelaContext *context, void *userData)
{
    

    // Close the server socket
    close(server_fd);
}

also when i click the STOP BUTTON the code continues. it stops after sending another message from the tcp client. what causes this behaviour?

i´m guessing that none of the dependencies is the problem because these are the same dependencies as the udpServer. its rather a problem i handle the auxilaryTask ?

giuliomoro

D300 also when i click the STOP BUTTON the code continues. it stops after sending another message from the tcp client. what causes this behaviour?

maybe accept() is blocking?

giuliomoro

Calling accept() from the audio thread causes a mode switch. Why don't you call it from the auxiliary task?

D300

giuliomoro unfortunately accept() is not blocking it, how can i trace back the problem, function call to functin call?

giuliomoro

it must be recv() that is blocking then. Either make it non-blocking or call select()/poll() before receiving.

D300

giuliomoro make it non-blocking

i added

// Set the client socket to non-blocking mode
        int flags = fcntl(client_socket, F_GETFL, 0);
        fcntl(client_socket, F_SETFL, flags | O_NONBLOCK);

but it had no effect... also the polling did not work - do I miss something?

// Create a pollfd structure for the client socket
        struct pollfd fds[1];
        fds[0].fd = client_socket;
        fds[0].events = POLLIN;

        // Wait for data to be available or timeout (1ms)
        int result = poll(fds, 1, 1);
        if (result == -1) {
            rt_printf("poll error\n");
            close(client_socket);
            continue;
        } else if (result == 0) {
            // Timeout occurred, no data available
            close(client_socket);
            continue;
        }

giuliomoro

btw the man page for accept() says:

If no pending connections are present on the queue, and the socket is not marked as nonblocking, accept() blocks the caller until a connection is present. If the socket is marked nonblocking and no pending connections are present on the queue, accept() fails with the error EAGAIN or EWOULDBLOCK.

I don't see your socket being set to non-blocking anywhere in your code.

giuliomoro

D300 } else if (result == 0) {
// Timeout occurred, no data available
close(client_socket);
continue;
}

you shouldn't close() if no error occurs.

D300 // Wait for data to be available or timeout (1ms)

make it 50ms so you save some spurious wakeups but at the same time are responsive enough to exit the loop on exit.

D300 if (result == -1) {
rt_printf("poll error\n");
close(client_socket);
continue;
}

If you close(), then you should also exit the loop or reopen the socket, but there is no point in continueing after a close().

D300

giuliomoro
back on the project, i´m still trying to figure out what causes the blocking...

while (!Bela_stopRequested()) 
    {
        
        // Accept new connections
        if ((client_socket = accept(server_fd, NULL, NULL)) < 0) 
        {
            rt_printf("accept failed\n");
            continue;
        }
        
        /*
        // Set the client socket to non-blocking mode
        int flags = fcntl(client_socket, F_GETFL, 0);
        fcntl(client_socket, F_SETFL, flags | O_NONBLOCK);
        rt_printf("SET NON-BLOCKING\n");

        // Create a pollfd structure for the client socket
        struct pollfd fds[1];
        fds[0].fd = client_socket;
        fds[0].events = POLLIN;
		
	
        // Wait for data to be available or timeout (50ms)
        int result = poll(fds, 1, 10);
        rt_printf("wait for data... \n");
        
        
        if (result == -1) 
        {
            rt_printf("poll error\n");
            close(client_socket);
            break;

        } 
        else if (result == 0) 
        {
            // Timeout occurred, no data available
            rt_printf("time out... \n");
            continue;
        }
		
        // Data is available, receive it
        int valread = recv(client_socket, buffer, BUFFER_SIZE, 0);
        rt_printf("recv function \n");
        
        if (valread > 0) 
        {
            rt_printf("Received: %s\n", buffer);
            
            // look for keywords
            for(unsigned int n = 0; n < valread; ++n)
			{
				printf("%c", buffer[n]);
				keyToFind[n] = buffer[n];
			}
			printf("\n");
			
			char keyword[20];
			char value[20];
			filterKeywordAndValue(keyToFind, keyword, value);

			for (unsigned int i = 0; i < NUM_KEYWORDS; i++ )
			{
				if ( strcmp(keyword, keywords_names[i]) == 0 ) // if keyword matches
				{
					// whats the match? 
					printf("Keyword Match!\n");
					
					printf("Keyword: %s\n", keyword);
					printf("Value: %s\n", value);
					
					// set value for audio backend
					if ( i == 0 )
					{
						s_uxs1.playState = atoi(value);
					}
					else if ( i == 1 ) // uxs2
					{
						s_uxs2.playState = atoi(value);
					}
					else if ( i == 2 ) // interrupt
					{
						gInterrupt = atoi(value);
					}
					else if ( i == 3 ) // mastervolume
					{
						gMasterVolume = atof(value);						
					}					
				}
			}

            // Send response to the client
            send(client_socket, response, strlen(response), 0);
            rt_printf("Response sent.\n");
        }
        */
        

        // Close the client socket
        close(client_socket);
    }

when i only have the uppest code part which is:

// Accept new connections
        if ((client_socket = accept(server_fd, NULL, NULL)) < 0) 
        {
            rt_printf("accept failed\n");
            continue;
        }

i have also the issue with BELA not responding when pressin the stop in the BELA IDE.
is there anything else i could try to track the problem? setting prints does help me to debug right now :/

giuliomoro

the most reliably way of debugging this is to run the program inside gdb.
In a terminal:

ssh root@bela.local 
cd Bela/projects/MYPROJECT # <<< replace MYPROJECT with the name of you project here and below
gdb ./MYPROJECT
# now you are inside gdb and you see the `(gdb)` prompt
run
# the program has started, let it run for a few seconds then when you are ready to stop it do:
# - press CTRL-C, then type:
signal SIGINT
continue
# at this point it should resume execution and threads should exit
# but if yours still hangs, as it does in the IDE, then press  CTRL-C again and type
info threads
# this will show what threads are still active and where (what function) they are in. Each thread
# has a numeric ID associated with it. They also have names, one of which should match the
# string you passed when you created the auxiliary task. Say that's thread 2, you can switch to it using:
thread 2
# If you don't recognise the function name that thread is in, it may be 
# because it's a low level call that has been called by some function in your code. 
# So you can use the backtrace command to see the call stack:
backtrace

That should give you enough to work with. If you want to continue the execution type continue, if you want to restart type run and if you want to exit type quit.