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