I try to initial a UDP client from threading, but it doesn't work? why?
These codes from the textbook
#define ECHOMAX 255 /* Longest string to echo */
#define TIMEOUT_SECS 2 /* Seconds between retransmits */
#define MAXTRIES 5 /* Tries before giving up */
int tries=0; /* Count of times sent - GLOBAL for signal-handler access */
void CatchAlarm(int ignored) /* Handler for SIGALRM */
{
tries += 1;
}
static void DieWithError(char *errorMessage)
{
perror(errorMessage);
exit(1);
}
void TCP () {
int sock; /* Socket descriptor */
struct sockaddr_in echoServAddr; /* Echo server address */
struct sockaddr_in fromAddr; /* Source address of echo */
unsigned short echoServPort; /* Echo server port */
unsigned int fromSize; /* In-out of address size for recvfrom() */
struct sigaction myAction; /* For setting signal handler */
char *servIP; /* IP address of server */
char *echoString; /* String to send to echo server */
char echoBuffer[ECHOMAX+1]; /* Buffer for echo string */
int echoStringLen; /* Length of string to echo */
int respStringLen; /* Size of received datagram */
//The IP is invalid since I need to test the function about timeout!!
servIP = "192.168.1.254"; /* First arg: server IP address (dotted quad) */
echoString = "abc"; /* Second arg: string to echo */
if ((echoStringLen = strlen(echoString)) > ECHOMAX)
DieWithError("Echo word too long");
echoServPort = atoi("12345"); /* Use given port, if any */
/* Create a best-effort datagram socket using UDP */
if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
DieWithError("socket() failed");
/* Set signal handler for alarm signal */
myAction.sa_handler = CatchAlarm;
if (sigfillset(&myAction.sa_mask) < 0) /* block everything in handler */
DieWithError("sigfillset() failed");
myAction.sa_flags = 0;
if (sigaction(SIGALRM, &myAction, 0) < 0)
DieWithError("sigaction() failed for SIGALRM");
/* Construct the server address structure */
memset(&echoServAddr, 0, sizeof(echoServAddr)); /* Zero out structure */
echoServAddr.sin_family = AF_INET;
echoServAddr.sin_addr.s_addr = inet_addr(servIP); /* Server IP address */
echoServAddr.sin_port = htons(echoServPort); /* Server port */
/* Send the string to the server */
if (sendto(sock, echoString, echoStringLen, 0, (struct sockaddr *)
&echoServAddr, sizeof(echoServAddr)) != echoStringLen)
DieWithError("sendto() sent a different number of bytes than expected");
/* Get a response */
fromSize = sizeof(fromAddr);
alarm(TIMEOUT_SECS); /* Set the timeout */
When I call this function from a thread, it is blocking here, and no response anymore!
while ((respStringLen = recvfrom(sock, echoBuffer, ECHOMAX, 0,
(struct sockaddr *) &fromAddr, &fromSize)) < 0) {
if (errno == EINTR) /* Alarm went off */
{
if (tries < MAXTRIES) /* incremented by signal handler */
{
printf("timed out, %d more tries...\n", MAXTRIES-tries);
if (sendto(sock, echoString, echoStringLen, 0, (struct sockaddr *)
&echoServAddr, sizeof(echoServAddr)) != echoStringLen)
DieWithError("sendto() failed");
alarm(TIMEOUT_SECS);
}
else
DieWithError("No Response");
}
else
DieWithError("recvfrom() failed");
}
/* recvfrom() got something -- cancel the timeout */
alarm(0);
/* null-terminate the received data */
echoBuffer[respStringLen] = '\0';
printf("Received: %s\n", echoBuffer); /* Print the received data */
close(sock);
exit(0);
}
These code does not work!
static void* testRun () {
TCP();
pthread_exit(NULL);
return NULL;
}
int main ( void ) {
pthread_t thread1;
assert( pthread_create( &thread1, NULL, &testRun, NULL) == 0 );
assert( pthread_join( thread1, NULL) == 0 );
while ( 1 ) {}
}
The following codes work!!! WHY? WHY? I ready have no idea!
int main ( void ) {
TCP();
while ( 1 ) {}
}
---------- Post updated at 12:30 PM ---------- Previous update was at 11:40 AM ----------
The problem properly cause by the signal and threading. But I still have no idea.
