socket and pthread

[AmeL]

Hi all.
I have a socket. I want to create two threads, one is to read from socket, and another is to write to socket. However, I want these two threads to be able to share the same data, so I created a mutex to lock the resource.
I don't know what happens with my two threads, but it always quits after it did some tasks.

#include "camel.h"
#include "irc.h" 
 
pthread_t         gtid;
pthread_mutex_t   gMutex;
 
// The shared resource between reading and writing thread
char              gSntBuffer[MAX_SIZE_BUFFER];
 
void*
SendRequest( INPUT void* pArg)
{
    int  lsockfd;
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION ENTRY",
           "")
    lsockfd = (int)pArg;       
    while(1)
    {
        pthread_mutex_lock(&gMutex);
 
        if (gSntBuffer)
        {
#ifdef DBG
            printf("Snt Buffer : %s\n", gSntBuffer);
#endif
            write(lsockfd, gSntBuffer, MAX_SIZE_BUFFER);
        }
 
        pthread_mutex_unlock(&gMutex);
    }
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION EXIT",
           "")        
}
 
void*
ReceiveReply( INPUT void* pArg)
{
    int   lsockfd = (int)pArg;
    char  lRcvBuffer[MAX_SIZE_BUFFER];
    int   lBytes  = 0;
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION ENTRY",
           "")    
    while(1)
    {
        lBytes = read(lsockfd, lRcvBuffer, MAX_SIZE_BUFFER);
#ifdef DBG
        printf("Rcv Buffer : %s", lRcvBuffer);
#endif
        // here I have to filter the lRcvBuffer and 
        // then write something back to socket by filling 
        // the gSntBuffer only and let the SendRequest()
        // do the rest of the job.
        // 
 
        // .... CODE HERE
    }
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION EXIT",
           "")        
}
 
tRtnCode
ConnectIRC( INPUT tProfile profile )
{
    int                lsockfd;
    struct sockaddr_in lservaddr;
    int                lrvalue;
 
    pthread_attr_t     lattr;
 
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION ENTRY",
           "")           
 
    memset(&lservaddr, 0, sizeof(lservaddr));
    lservaddr.sin_family      = AF_INET;
    lservaddr.sin_port        = htons(profile.port);
    lservaddr.sin_addr.s_addr = inet_addr(profile.server);
 
    if (0 >= (lsockfd = socket(AF_INET, SOCK_STREAM,0)))
    {
        DBGINT(1,
               ERROR_SOCK_CANNOT_CREATE,
               "lsockfd = ",
               lsockfd)
        return (ERROR_SOCK_CANNOT_CREATE);
    }
 
    printf("SendRequest() : losckfd = %d\n", lsockfd);
 
    if (0 < (lrvalue = connect(lsockfd, (struct sockaddr*)&lservaddr, sizeof(lservaddr))))
    {
        DBGINT(1,
               ERROR_SOCK_CANNOT_CONNECT,
               "connect() returns ",
               lrvalue)
        return (ERROR_SOCK_CANNOT_CONNECT);
    }
 
    // set attributes
    pthread_attr_init(&lattr);
    pthread_attr_setdetachstate(&lattr, PTHREAD_CREATE_DETACHED);
    pthread_attr_setscope(&lattr, PTHREAD_SCOPE_SYSTEM);
 
    // init mutex
    pthread_mutex_init(gMutex, NULL);
    pthread_mutex_lock(&gMutex);
 
    snprintf(gSntBuffer, 
             MAX_SIZE_BUFFER,
             IRC_USER,
             profile.username,
             "",
             "",
             profile.fullname,
             profile.nickname);
 
    pthread_mutex_unlock(&gMutex);
 
    // create 2 threads
    // - read data
    // - write data
 
    pthread_create(&gtid, &lattr, SendRequest,  (void*)lsockfd);
    pthread_create(&gtid, &lattr, ReceiveReply, (void*)lsockfd);
 
    DBGSTR(3,
           STATUS_SUCCESS,
           "FUNCTION EXIT",
           "")
}

[Banfa]

It's not in the posted code but you need to ensure that main does not exit (i.e. return) until your threads have finished.

[gpraghuram]

HI,
R u creating the thread a sdetached or attached thread?
If you are creating it as a attcahed thred the call pthread_join() and return after the call.

Raghu

[AmeL]

Thank gpraghuram
oh yes....you're right. I forget to set the attribute to be JOINABLE, and join them to the main thread, so that the main thread could wait for all of the child threads to be terminated.

[AmeL]

Anyway, how about the same resource shared by two threads ?
I have to use the pthread_mutex_t to lock it right ?
I am not sure when to lock the resource. Let's say, there are 2 threads, one is to write data, and another is to read data, so in either reading or writing, we lock the resource ? or we lock only when we write ?

[Banfa]

Lock for both reading and writing but for efficiency keep the lock for as short a time as possible.

If you don't lock for reading the writing thread may change the data in the middle of you reading it which could produce very strange results.