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In my program i am using timeval structure of time.h for a TCP/IP socket program, in which the client waits for a timeout value as specified by this structure value the structure initialization is as below

struct timeval tv; 
tv.tv_sec  = 10;  
tv.tv_usec = 0;

and setting socket options as is. Since recv() is a blocking call I've put a timeout:

setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv,sizeof(struct timeval)) ;

and receive data using recv() function. So to verify whether delay is ok I used two variables start & stop of type time_t:

time_t start=clock();
BytesRcvd = recv(sock, CacheBuffer1,  sizeof(CacheBuffer1), FLAG);
time_t stop=clock();
time_t difference=difftime(stop,start);

so as per the definitions what I expect is the recv() functions waits for maximum of 10 seconds until data is received via socket. From the server side I didn't send anything. But upon calculating the difference the value I've obtained is 10 but I didn't feel a 10 second delay for reception, but just in the range of milliseconds, so I assume it only took about 10 millisecond

What might be the issue?? Any thoughts?

[update from comment]

My socket is non-blocking that's why I used setsocketopt() function, and I want to wait for a timeout value of 10 Seconds ,ie; if within 10seconds no data is received I have to exit from the recv() function...

alk
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user3395801
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  • What is the global `errno` set to? Is your socket nonblocking? If it is, then that would make it not wait forever. `fcntl` would set the blocking options. What's the significance of 10 seconds? – Engineer2021 Mar 27 '14 at 12:03
  • My socket is non-blocking that's why I used setsocketopt() function, and I want to wait for a timeout value of 10 Seconds ,ie; if within 10seconds no data is received I have to exit from the recv() function... – user3395801 Mar 27 '14 at 12:11
  • You set blocking options with `fcntl`. Not `setsocketopt`. https://stackoverflow.com/a/1549344/2591612 – Engineer2021 Mar 27 '14 at 12:14
  • I don't think `clock()` is the right timing function to use here. Maybe `time()` instead? – John Zwinck Mar 27 '14 at 12:19
  • You didn't zero `tv.tv_usec.` Perhaps it contained a garbage value that is invalid (too big). Also look http://stackoverflow.com/questions/4181784/how-to-set-socket-timeout-in-c-when-making-multiple-connections – Jayesh Bhoi Mar 27 '14 at 12:24
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    If you want to block, why did you set the socket non-blocking?! – David Schwartz Mar 27 '14 at 15:48
  • Your question doesn't make sense. Non-blocking sockets don't block. – user207421 Mar 27 '14 at 20:58
  • I agree non-blocking doen't block, but the "ISSUE IS ABOUT THE TIME, I EXPECT A 10 SECOND DELAY AND NOT ABLE TO GET IT" – user3395801 Mar 28 '14 at 07:06

2 Answers2

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If your socket is non-blocking recv() won't block, even if you set a time-out.

Setting a time-out makes sense for blocking sockets, to not have them block for ever.

So if you want the recv() to block for a certain amount of time, set the socket to be blocking and apply the time-out as you did.

alk
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0

Your time calculation is quite wrong

clock() calculates CPU time spent on most platforms (Windows is an exception here). Blocking and waiting for data does not consume a lot of CPU time.

Moreover, clock() returns a clock_t, not a time_t, so passing it to difftime() doesn't make sense. clock() is also in units of CLOCKS_PER_SEC,so you will need to account for that if you want to convert the time difference to e.g. miliseconds or seconds.

For a start since your timeout is in the order of many seconds, use time() to calculate them time spent, the result will be in seconds. If you need something more granular, use e.g. gettimeofday()

time_t start=time();
BytesRcvd = recv(sock, CacheBuffer1,  sizeof(CacheBuffer1), FLAG);
time_t stop=time();
time_t difference=difftime(stop,start);
nos
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  • I doesn't need the exact time @ that moment , just the difference between the time of starting of the reception and end of reception, Since the clock() function returns a reference time to some value I think that might be sufficient – user3395801 Mar 28 '14 at 07:19
  • @user3395801 Well it certainly depends on the platform, but how is it useful to measure CPU time when you want to check if the timeout value is hit ? i.e. clock() might measure 1 microsecond of CPU time even if your call blocks for 2 minutes. And in any rate you would need to care about CLOCKS_PER_SEC, so you know if the value you print out is in microseconds, miliseconds or something else. – nos Mar 28 '14 at 07:34