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   1 /* Licensed under GPLv3+ - see LICENSE file for details */
   2 #include "config.h"
   3 #include <string.h>
   4
   5 /**
   6  * lbalance - helpers for loadbalancing parallel tasks
   7  *
   8  * This code helps when you have a large number of one-shot tasks; it tries
   9  * to determine the maximum amount of useful parallelism.
  10  *
  11  * License: GPL
  12  * Author: Rusty Russell <rusty@rustcorp.com.au>
  13  *
  14  * Example:
  15  *      // Run 1000 of the given commandline at best-known parallel rate.
  16  *      // See tools/lbalance.c for a sligtly more serious example.
  17  *      #include <ccan/lbalance/lbalance.h>
  18  *      #include <sys/types.h>
  19  *      #include <sys/time.h>
  20  *      #include <sys/resource.h>
  21  *      #include <sys/wait.h>
  22  *      #include <err.h>
  23  *
  24  *      #define MAX 1000
  25  *
  26  *      static pid_t spawn(char *args[])
  27  *      {
  28  *              pid_t pid = fork();
  29  *
  30  *              if (pid == -1)
  31  *                      err(1, "forking");
  32  *              if (pid == 0) {
  33  *                      execvp(args[0], args);
  34  *                      err(1, "exec failed");
  35  *              }
  36  *              return pid;
  37  *      }
  38  *
  39  *      int main(int argc, char *argv[])
  40  *      {
  41  *              unsigned int num = 0, num_running = 0;
  42  *              pid_t pids[MAX];
  43  *              struct lbalance_task *tasks[MAX];
  44  *              struct lbalance *lb;
  45  *
  46  *              if (argc == 1)
  47  *                      errx(1, "Usage: %s cmdline...", argv[0]);
  48  *
  49  *              lb = lbalance_new();
  50  *
  51  *              while (num - num_running < MAX) {
  52  *                      struct rusage ru;
  53  *                      pid_t pid;
  54  *                      unsigned int i;
  55  *
  56  *                      // Make sure we're running as many as lbalance says to.
  57  *                      while (num_running < lbalance_target(lb) && num < MAX) {
  58  *                              pids[num] = spawn(argv+1);
  59  *                              tasks[num] = lbalance_task_new(lb);
  60  *                              num++;
  61  *                              num_running++;
  62  *                      }
  63  *
  64  *                      // Now wait for something to die.
  65  *                      pid = wait3(NULL, 0, &ru);
  66  *                      // Find it, tell lbalance it's finished.
  67  *                      for (i = 0; i < num; i++) {
  68  *                              if (pids[i] == pid) {
  69  *                                      lbalance_task_free(tasks[i], &ru);
  70  *                                      pids[i] = 0;
  71  *                                      break;
  72  *                              }
  73  *                      }
  74  *                      num_running--;
  75  *              }
  76  *              lbalance_free(lb);
  77  *              return 0;
  78  *      }
  79  */
  80 int main(int argc, char *argv[])
  81 {
  82         /* Expect exactly one argument */
  83         if (argc != 2)
  84                 return 1;
  85
  86         if (strcmp(argv[1], "depends") == 0) {
  87                 printf("ccan/tlist\n");
  88                 return 0;
  89         }
  90
  91         return 1;
  92 }