procexec/multi_wait.cThis is procexec/multi_wait.c (Listing 26-1, page 543), an example from the book, The Linux Programming Interface. The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3. This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below. In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions. |
+/* multi_wait.c + + Demonstrate the use of wait(2): create multiple children and then wait + for them all. + + Usage: multi_wait sleep-time... + + One child process is created for each command-line argument. Each child + sleeps for the number of seconds specified in the corresponding command-line + argument before exiting. After all children have been created, the parent + loops, waiting for terminated children, and displaying their PIDs. +*/ #include <sys/wait.h> #include <time.h> #include "curr_time.h" /* Declaration of currTime() */ #include "tlpi_hdr.h" int main(int argc, char *argv[]) { int numDead; /* Number of children so far waited for */ pid_t childPid; /* PID of waited for child */ int j; if (argc < 2 || strcmp(argv[1], "--help") == 0) usageErr("%s sleep-time...\n", argv[0]); setbuf(stdout, NULL); /* Disable buffering of stdout */ for (j = 1; j < argc; j++) { /* Create one child for each argument */ switch (fork()) { case -1: errExit("fork"); case 0: /* Child sleeps for a while then exits */ printf("[%s] child %d started with PID %ld, sleeping %s " "seconds\n", currTime("%T"), j, (long) getpid(), argv[j]); sleep(getInt(argv[j], GN_NONNEG, "sleep-time")); _exit(EXIT_SUCCESS); default: /* Parent just continues around loop */ break; } } numDead = 0; for (;;) { /* Parent waits for each child to exit */ childPid = wait(NULL); if (childPid == -1) { if (errno == ECHILD) { printf("No more children - bye!\n"); exit(EXIT_SUCCESS); } else { /* Some other (unexpected) error */ errExit("wait"); } } numDead++; printf("[%s] wait() returned child PID %ld (numDead=%d)\n", currTime("%T"), (long) childPid, numDead); } }
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