?
Solved

Timeout

Posted on 2000-02-19
2
Medium Priority
?
2,028 Views
Last Modified: 2013-12-26
I am writing a echo server/client program in Unix.
I have executed the following statement to send and receive a UDP packet.

while (1) {
sendto(outFd, data, dataLength, 0, (struct sockaddr*)&outAddr, sizeof(outAddr))
int n = recvfrom(inFd, buffer, length, 0, (struct sockaddr*) &inAddr, &inAddLen
);

if (timeout)continue;
else break;
}

Since UDP is not reliable, so the recvfrom()sometimes never get back it echo. So I would like to add a timeout handle. If recvfrom() is timeout, then the program would go back to sendto() and send data again.

I know I should use signal and alarm. But what I should exactly add to my program so that when the recvfrom() time out, the signal handler would help me to "skip" the recvfrom() and do sendto() again?
0
Comment
Question by:matchz
2 Comments
 
LVL 3

Accepted Solution

by:
ufolk123 earned 600 total points
ID: 2539533
matchz,

better is you do not bet on signals and alarms.You can use select() which comes handy for this purpose.in select() call you can specify the timeout in millisec resoultion.So you can wait for some time and try sendto again if select returns timeout.
fd_set RecFd,ErrFd;
const struct timeval * timeout ;

/** Put app timeout values here ***/
timeout.tv_sec=0;
timeout.tv_use=0;
/****************************/

while (1) {
                   sendto(outFd, data, dataLength, 0, (struct sockaddr*)&outAddr, sizeof(outAddr)) ;
                   /*** Code for timeout **/
                  FD_SET(inFd, &RecFd)
                  FD_SET(inFd, &ErrFd)
                  select ( inFd+1, &RecFd,NULL,&ErrFd, &timeout);
                  if( FD_ISSET(inFd, &RecFd)  //OK
                      int n = recvfrom(inFd, buffer, length, 0, (struct sockaddr*) &inAddr, &inAddLen
                 else if( FD_ISSET(inFd, &ErrFd)  //Socket problem
                      /* Take action for sock error */
                 else // Timeout happened
                     break;
            );
 


This is just outline code.You may have to check return value of select() etc for catching all failure conditions.But on a whole you can use this construct to acheive you goal.


0
 

Author Comment

by:matchz
ID: 2547369
While I am seldom to write program on Unix perform. I know very less in Unix programming.
Thank you for your answer and my program work now!
^_^
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction: Hints for the grid button.  Nested classes, templated collections.  Squash that darned bug! Continuing from the sixth article about sudoku.   Open the project in visual studio. First we will finish with the SUD_SETVALUE messa…
Ready to get certified? Check out some courses that help you prepare for third-party exams.
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
This video shows how to quickly and easily deploy an email signature for all users in Office 365 and prevent it from being added to replies and forwards. (the resulting signature is applied on the server level in Exchange Online) The email signat…
Suggested Courses
Course of the Month9 days, 9 hours left to enroll

609 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question