Fork()

Drainy · 11-13-2009, 07:26 AM

Hi,

I am currently having issue with a fork command I am issuing, I am attempting to use fork to create x number of identical processes however it is creating the required amount and then the child appears to enter into the same fork and create another x amount of forks, is there a trick to avoid this? I am using a for loop to increment until I hit the x amount of forks required.

I am not looking for code but just some sort of logical thinking around this problem so I can try and get over this hurdle myself.

Thanks

nadroj · 11-13-2009, 10:08 AM

Its hard to understand what your doing without seeing the code. Its been a little while since Ive used "fork", etc, but if your doing something like this

Code:

int i;
for ( i=0; i < MAX; i++ )
{
   fork();
   childFunction(); // this should never return to here
}

you should do

Code:

int i;
for ( i=0; i < MAX; i++ )
{
   if ( fork() == 0 ) // only the child should call the childFunction
   {   
      childFunction(); // this should never return to here
   }
}

Also, the key is that "childFunction()" never returns to the calling function. If you have something like

Code:

int childFunction() // whatever return type
{
  // do something
  return 5; // return something
}

this child process will return to the calling process, and continue its own "version" of the for loop, the child itself creating its own children (recursively). This is obviously a bad thing. As mentioned, you have to make sure this child function never returns, i.e.

Code:

int childFunction() // whatever return type
{
  // do something
  // kill this process (using kill and getpid()) or simply use an "exit" call so this process ends (exit(0))
  return 5; // required by language to return something, even though it never will (because process would have ended on previous line)
}

11-13-2009, 07:26 AM	#1
Drainy Registered User Join Date: Mar 2005 Posts: 24	Fork() Hi, I am currently having issue with a fork command I am issuing, I am attempting to use fork to create x number of identical processes however it is creating the required amount and then the child appears to enter into the same fork and create another x amount of forks, is there a trick to avoid this? I am using a for loop to increment until I hit the x amount of forks required. I am not looking for code but just some sort of logical thinking around this problem so I can try and get over this hurdle myself. Thanks
Drainy is offline

11-13-2009, 10:08 AM	#2
nadroj Registered User Join Date: Oct 2006 Location: Canada Posts: 1,230	Its hard to understand what your doing without seeing the code. Its been a little while since Ive used "fork", etc, but if your doing something like this Code: int i; for ( i=0; i < MAX; i++ ) { fork(); childFunction(); // this should never return to here } you should do Code: int i; for ( i=0; i < MAX; i++ ) { if ( fork() == 0 ) // only the child should call the childFunction { childFunction(); // this should never return to here } } Also, the key is that "childFunction()" never returns to the calling function. If you have something like Code: int childFunction() // whatever return type { // do something return 5; // return something } this child process will return to the calling process, and continue its own "version" of the for loop, the child itself creating its own children (recursively). This is obviously a bad thing. As mentioned, you have to make sure this child function never returns, i.e. Code: int childFunction() // whatever return type { // do something // kill this process (using kill and getpid()) or simply use an "exit" call so this process ends (exit(0)) return 5; // required by language to return something, even though it never will (because process would have ended on previous line) }
nadroj is offline

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