I basically want to inform main that a client disconnected in order to decrement the thread counter. Right now my program is setup to only create a certain number of threads to serve the connecting clients. If the client disconnects the thread count needs to be decremented so that it does not max out and not allow further threads to be made for waiting clients.
Now I can use a global variable, but I am doing this to learn more about Unix system programming and I thought either pipes or message queues would be interesting to try out. My problem is I am not sure how my code can utilize this to send information from child thread to main thread.
I wrote some quick and dirty code as an to test out different ways of what I need to do.
In my code I commented where I want to send message back to main process.
I have client code if you do need I can post, but the code below should be sufficient.
Thanks for any help!
Code:
#include <stdio.h>
#include <pthread.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <strings.h>
#include <stdlib.h>
#include <unistd.h>
#define BUFFERSIZE 512
#define NTHREADS 10
#define SERVER_PORT 6001
#define POOL_SIZE 5
void *main_client_thread(void *arg);
typedef struct mainthreadArg
{
int csocketId;
int threadCounter;
}mtArg;
int main(int argc, char** argv)
{
int csock, ssock;
socklen_t addr_len;
pthread_t cthread[NTHREADS];
struct sockaddr_in addr;
bzero((void *)&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(SERVER_PORT);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
addr_len = sizeof(addr);
/* socket */
if((ssock=socket(PF_INET, SOCK_STREAM, 0))==-1)
{
fprintf(stderr,"Unable to create server socket\n");
exit(1);
}
/* bind */
if(bind(ssock, (struct sockaddr *)&addr, sizeof(addr))==-1)
{
fprintf(stderr,"bind failed.\n");
exit(1);
}
/* listen */
if(listen(ssock, POOL_SIZE)==-1)
{
fprintf(stderr, "listen failed.\n");
exit(1);
}
mtArg ta;
ta.threadCounter = 0; /* thread counter */
/* main loop to manage clients */
while(1)
{
if(ta.threadCounter > NTHREADS)
{
printf("No more threads can be created. Sorry\n");
exit(1);
}
/* accept */
if((csock=accept(ssock, (struct sockaddr *)&addr, &addr_len))==-1)
{
fprintf(stderr, "accept failed.\n");
exit(1);
}
ta.csocketId = csock;
if((pthread_create(&cthread[ta.threadCounter], NULL, main_client_thread, &ta)) != 0)
{
fprintf(stdout, "pthread was not created\n");
exit(0);
}
ta.threadCounter++;
}
return 0;
}
void *main_client_thread(void *arg)
{
mtArg t = *(mtArg *)arg;
int cli,cnt;
cli = t.csocketId;
cnt = t.threadCounter;
int stayConnected = 1;
int nread;
/* int nwrite; */
char buffer[BUFFERSIZE];
while(stayConnected == 1)
{
bzero(buffer, sizeof(buffer));
if((nread=read(cli, buffer, BUFFERSIZE)) > 0)
{
printf("Thread %d read %d bytes from client.\n", t.threadCounter, nread);
printf("Thread %d buffer=%s\n", t.threadCounter, buffer);
}
else /* client disconnected */
{
printf("nread failed.\n");
t.threadCounter--;
/* report back to main thread so that thread counter is decremented */
/* use pipe or message queue for this */
stayConnected = 0;
}
}
return NULL;
}
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Can I create multiple threads using single thread_id
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Discussion started by: murali242512
2 Replies
LEARN ABOUT POSIX
sendmmsg
SENDMMSG(2) Linux Programmer's Manual SENDMMSG(2)NAME
sendmmsg - send multiple messages on a socket
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sys/socket.h>
int sendmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen,
int flags);
DESCRIPTION
The sendmmsg() system call is an extension of sendmsg(2) that allows the caller to transmit multiple messages on a socket using a single
system call. (This has performance benefits for some applications.)
The sockfd argument is the file descriptor of the socket on which data is to be transmitted.
The msgvec argument is a pointer to an array of mmsghdr structures. The size of this array is specified in vlen.
The mmsghdr structure is defined in <sys/socket.h> as:
struct mmsghdr {
struct msghdr msg_hdr; /* Message header */
unsigned int msg_len; /* Number of bytes transmitted */
};
The msg_hdr field is a msghdr structure, as described in sendmsg(2). The msg_len field is used to return the number of bytes sent from the
message in msg_hdr (i.e., the same as the return value from a single sendmsg(2) call).
The flags argument contains flags ORed together. The flags are the same as for sendmsg(2).
A blocking sendmmsg() call blocks until vlen messages have been sent. A nonblocking call sends as many messages as possible (up to the
limit specified by vlen) and returns immediately.
On return from sendmmsg(), the msg_len fields of successive elements of msgvec are updated to contain the number of bytes transmitted from
the corresponding msg_hdr. The return value of the call indicates the number of elements of msgvec that have been updated.
RETURN VALUE
On success, sendmmsg() returns the number of messages sent from msgvec; if this is less than vlen, the caller can retry with a further
sendmmsg() call to send the remaining messages.
On error, -1 is returned, and errno is set to indicate the error.
ERRORS
Errors are as for sendmsg(2). An error is returned only if no datagrams could be sent. See also BUGS.
VERSIONS
The sendmmsg() system call was added in Linux 3.0. Support in glibc was added in version 2.14.
CONFORMING TO
sendmmsg() is Linux-specific.
NOTES
The value specified in vlen is capped to UIO_MAXIOV(1024).
BUGS
If an error occurs after at least one message has been sent, the call succeeds, and returns the number of messages sent. The error code is
lost. The caller can retry the transmission, starting at the first failed message, but there is no guarantee that, if an error is
returned, it will be the same as the one that was lost on the previous call.
EXAMPLE
The example below uses sendmmsg() to send onetwo and three in two distinct UDP datagrams using one system call. The contents of the first
datagram originates from a pair of buffers.
#define _GNU_SOURCE
#include <netinet/ip.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
int
main(void)
{
int sockfd;
struct sockaddr_in addr;
struct mmsghdr msg[2];
struct iovec msg1[2], msg2;
int retval;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == -1) {
perror("socket()");
exit(EXIT_FAILURE);
}
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
addr.sin_port = htons(1234);
if (connect(sockfd, (struct sockaddr *) &addr, sizeof(addr)) == -1) {
perror("connect()");
exit(EXIT_FAILURE);
}
memset(msg1, 0, sizeof(msg1));
msg1[0].iov_base = "one";
msg1[0].iov_len = 3;
msg1[1].iov_base = "two";
msg1[1].iov_len = 3;
memset(&msg2, 0, sizeof(msg2));
msg2.iov_base = "three";
msg2.iov_len = 5;
memset(msg, 0, sizeof(msg));
msg[0].msg_hdr.msg_iov = msg1;
msg[0].msg_hdr.msg_iovlen = 2;
msg[1].msg_hdr.msg_iov = &msg2;
msg[1].msg_hdr.msg_iovlen = 1;
retval = sendmmsg(sockfd, msg, 2, 0);
if (retval == -1)
perror("sendmmsg()");
else
printf("%d messages sent
", retval);
exit(0);
}
SEE ALSO recvmmsg(2), sendmsg(2), socket(2), socket(7)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2018-02-02 SENDMMSG(2)
07-06-2012
