On Mon, 2010-01-11 at 15:01 +0530, Pete wrote:
> After going through this thread, I just tried out the following simple
> code:
>
> int main (void) {
>
> int pid;
>
> int *testVar = (int *) malloc (sizeof (int));
>
> *testVar = 10;
>
> printf ("%d [%d] Main \n", *testVar, testVar);
>
> pid=vfork(); // works fine if we use fork instead.
>
> if (pid==0) {
>
> printf ("Child %d [%d]\n", *testVar, testVar);
>
> return 1;
>
> } else if (pid > 0) {
>
> printf ("Parent %d [%d]\n", *testVar, testVar);
>
> *testVar=11; // segfault if we use vfork, as vfork blocks until child
> returns call exec/exits.
>
> wait(NULL);
>
> printf ("Parent %d [%d]\n", *testVar, testVar);
>
> return 1;
>
> }
>
> exit(0);
> }
>
> can someone let me know why this segfaults with vfork and not with fork?
> >From my understanding - it is because the parent is blocked until the
> child exec's/exits AND in the mean time when the program is being
> executed the child/parent process is trying to change the *testVar is
> causing to modify the parents read-only memory. CMIAW.
>
> Another thing I noticed is on linux the child always gets to run first
> in case of fork() and vfork()?
In my opinion - its because vfork() function has the same effect as
fork(), except that the behaviour is undefined if the process created by
vfork() either modifies any data other than a variable of type pid_t
used to store the return value from vfork(), or returns from the
function in which vfork() was called, or calls any other function before
successfully calling _exit() OR one of the exec family of functions.
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