CODEWITHSUNDEEP
clinuxunixfork
Complex
Complex

Reputation: 29

Are my fork processes running parallel or executing one after another?

I am just going to post pseudo code, but my question is I have a loop like such

for(i<n){
   createfork();
   if(child)
       /*
         Exit so I can control exact amount of forks 
         without children creating more children
        */
       exit
}


void createfork(){
 fork
 //execute other methods
}

Does my fork create a process do what it is suppose to do and exit then create another process and repeat? And if so what are some ways around this, to get the processes running concurrently?

Upvotes: 0

Views: 2337

Answers (2)

John Kugelman
John Kugelman

Reputation: 361585

Your pseudocode is correct as written and does not need to be modified.

The processes are already executing in parallel, all six of them or however many you spawn. As written, the parent process does not wait for the children to finish before spawning more children. It calls fork(), checks if (child) (which is skipped), then immediately proceeds to the next for loop iteration and forks again.

Notably, there's no wait() call. If the parent were to call wait() or waitpid() to wait for each child to finish then that would introduce the serialism you're trying to avoid. But there is no such call, so you're good.

Upvotes: 4

John Bollinger
John Bollinger

Reputation: 180113

When a process successfully performs a POSIX fork(), that process and the new child process are initially both eligible to run. In that sense, they will run concurrently until one or the other blocks. Whether there will be any periods of time when both are executing machine instructions (on different processing units) depends at least on details of hardware capabilities, OS scheduling, the work each process is performing, and what other processes there are in the system and what they are doing.

The parent certainly does not, in general, automatically wait for the child to terminate before it proceeds with its own work (there is a family of functions to make it wait when you want that), nor does the child process automatically wait for any kind of signal from the parent. If the next thing the parent does is fork another child, then that will under many circumstances result in the parent running concurrently with both (all) children, in the sense described above.

I cannot speak to specifics of the behavior of your pseudocode, because it's pseudocode.

Upvotes: -1

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