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/* The goal here is to create N forked processes and loop a list of 'jobs' | |
* and submit each to a free fork when it becomes free */ | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include <unistd.h> | |
#include <sys/types.h> | |
#include <sys/wait.h> | |
#include <time.h> | |
#define MAXCHILD 8 | |
pid_t children[MAXCHILD]; | |
/* Sleep random time between 500 and 1000 msec */ | |
int takesometime() | |
{ | |
int msec; | |
srand(getpid()); | |
msec = rand() % 1000 + 1000; | |
printf("[%05d] Doing \"work\" for %d milliseconds\n", getpid(), msec); | |
fflush(stdout); | |
return usleep(msec * 1000); | |
} | |
int childbypid(int pid) | |
{ | |
int child; | |
for (child = 0; child < MAXCHILD; child++) { | |
if (children[child] == pid) { | |
children[child] = 0; | |
return child; | |
} | |
} | |
return -1; | |
} | |
int findfreechild() | |
{ | |
int child; | |
for (child = 0; child < MAXCHILD; child++) { | |
printf("Checking child %d\n", child); | |
fflush(stdout); | |
if (children[child] == 0) { | |
printf("Child %d is free\n", child); | |
fflush(stdout); | |
return child; | |
} | |
} | |
return -1; | |
} | |
void cleanchildren() | |
{ | |
for (int child = 0; child < MAXCHILD; child ++) { | |
children[child] = 0; | |
} | |
} | |
int countchildren() | |
{ | |
int count = 0; | |
for (int child = 0; child < MAXCHILD; child ++) { | |
if (children[child] > 0) { | |
count++; | |
} | |
} | |
return count; | |
} | |
int main(int argc, char *argv[]) | |
{ | |
pid_t childpid; | |
int event; | |
int events = 16; | |
int freeproc = -1; | |
int status; | |
cleanchildren(); | |
/* Start children. */ | |
for (event = 0; event < events; ++event) { | |
/* Get next free child or wait for one to exit */ | |
if ((freeproc = findfreechild()) == -1) { | |
freeproc = childbypid(wait(&status)); | |
} | |
/* Fork process */ | |
if ((childpid = fork()) < 0) { | |
perror("fork"); | |
abort(); | |
} else if (childpid == 0) { | |
takesometime(); | |
exit(0); | |
} | |
children[freeproc] = childpid; | |
} | |
/* END: Wait for children to exit. */ | |
printf("Done jobs\n"); | |
while (countchildren() > 0) { | |
childpid = wait(&status); | |
printf("Child with PID %d exited with status 0x%x.\n", childpid, status); | |
children[childbypid(childpid)] = 0; | |
} | |
return 0; | |
} |
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