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inter process communication

Posted on 2004-09-14
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Last Modified: 2010-04-15
I have a program with a child and a parent process.

How can one process notify the other process that an event has occurred (by using signals) ?

please provide some code examples.
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Question by:FOXBAT
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Expert Comment

by:sunnycoder
ID: 12052868
Hi FOXBAT,

what platform ?

Sunnycoder
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Expert Comment

by:sunnycoder
ID: 12052877
use kill to send a signal

#include <sys/types.h>

#include <signal.h>

int kill(pid_t pid, int sig);

http://www.die.net/doc/linux/man/man2/kill.2.html

parent gets a child pid when child is spawned and child can get parent pid by calling getppid()
http://www.die.net/doc/linux/man/man2/getppid.2.html
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sunnycoder earned 150 total points
ID: 12052898
Here are some examples and details
http://www.cs.cf.ac.uk/Dave/C/node24.html#SECTION002400000000000000000

http://www.delorie.com/gnu/docs/glibc/libc_503.html

I would recommend using sigaction interface instead of signal interface
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Author Comment

by:FOXBAT
ID: 12052901
can you please modify this code to send a signal from one process to the other

if(pid == 0) // child
{  
      printf("child %d is sleeping \n", getpid());
      sleep(1);
}


while(waitpid(pid, &status, WNOHANG) == 0) // parent
{
      printf("waitin....\n");
      sleep(1);

}
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Expert Comment

by:sunnycoder
ID: 12052916
who should send signal to whom and which signal ? .. added a line below

if(pid == 0) // child
{  
     printf("child %d is sleeping \n", getpid());
     sleep(1);
}


while(waitpid(pid, &status, WNOHANG) == 0) // parent
{
     printf("waitin....\n");
     sleep(1);
     kill (pid, SIGUSR1);  <-- parent will send SIGUSR1 to child. Since you used pid == 0 to check for a child, I assume that pid holds the pid for the child and appropriate error checking for fork has been done
}
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Author Comment

by:FOXBAT
ID: 12052965
ok so how does the child recive the signal?

can you please provide the example in the code above
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Expert Comment

by:sunnycoder
ID: 12052990
Check the second link I posted for a complete example
http://www.delorie.com/gnu/docs/glibc/libc_503.html
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Expert Comment

by:grg99
ID: 12055466
The signal() way of communication is a rather narrow and slow channel.

If you just want to pass a byte every second, signal is okay.

If you need much more bandwidth, I'd use a TCP connection.  

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