02-16-2005
parent and child process question?
Hi everybody,
I'm trying to understand how a parent and child processes interact.
This function( below) basically measures the fork time from the perspective of the parent only.
what i would like to know is how to measure the time from the perspective of parent and child (ie: inserting the GETTIME(endt) inside the child).
Any help would be appreciated.
HTML Code:
void run_tests(int nt)
{
struct timeval begt;
struct timeval endt;
double secs;
int i;
pid_t pid;
int waitid;
int status;
double max_secs = 0.000000;
double min_secs = 0.000000;
double average = 0.000000;
double sum = 0.000000;
for(i=0; i<nt; i++)
{
GETTIME(begt); // gettimeofday()
if((pid = fork()) < 0)
{
perror("fork() failed!\n");
_exit(1);
}
if( pid == 0)
{
_exit(0);
}
waitid = wait(&status);
GETTIME(endt); // gettimeofday()
secs = TOTALSECS(begt,endt);
max_secs = max(secs,max_secs);
min_secs = min(secs,min_secs);
sum += secs;
printf("%2d: secs = %.6f\n", i,secs);
} /* end of FOR loop */
average = sum / (i + 1);
printf("min: %.6f\n", min_secs);
printf("max: %.6f\n", max_secs);
printf("sum: %.6f\n", sum);
printf("average: %.6f\n", average);
printf("waitid: %d \n", waitid);
printf(" \n");
}
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fork(2) System Calls Manual fork(2)
Name
fork - create a new process
Syntax
#include <sys/types.h>
#include <unistd.h>
pid = fork()
pid_t pid;
Description
The system call causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the
following:
o The child process has a unique process ID.
o The child process has a different parent process ID (that is, the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that, for
instance, file pointers in file objects are shared between the child and the parent, so that a on a descriptor in the child process
can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish standard input
and output for newly created processes as well as to set up pipes.
o The child processes resource utilizations are set to 0. For further information, see
Return Values
Upon successful completion, returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
Diagnostics
The system call fails and no child process are created under the following conditions:
[EAGAIN] The system-imposed limit {PROC_MAX} on the total number of processes under execution would be exceeded.
[EAGAIN] The system-imposed limit {CHILD_MAX} on the total number of processes under execution by a single user would be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
See Also
execve(2), wait(2)
fork(2)