text: /* This testcase is part of GDB, the GNU debugger.
  
     Copyright 2015-2017 Free Software Foundation, Inc.
  
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 3 of the License, or
     (at your option) any later version.
  
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  
  #define _GNU_SOURCE
  #include <assert.h>
  #include <pthread.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <stdio.h>
  #include <limits.h>
  
  /* How many threads fit in the target's thread number space.  */
  long tid_max = -1;
  
  /* Number of threads spawned.  */
  unsigned long thread_counter;
  
  /* How long it takes to spawn as many threads as fits in the thread
     number space.  On systems where thread IDs are just monotonically
     incremented, this is enough for the tid numbers to wrap around.  On
     targets that randomize thread IDs, this is enough time to give each
     number in the thread number space some chance of reuse.  It'll be
     capped to a lower value if we can't compute it.  */
  unsigned int reuse_time = -1;
  
  void *
  do_nothing_thread_func (void *arg)
  {
    usleep (1);
    return NULL;
  }
  
  void *
  spawner_thread_func (void *arg)
  {
    while (1)
      {
        pthread_t child;
        int rc;
  
        thread_counter++;
  
        rc = pthread_create (&child, NULL, do_nothing_thread_func, NULL);
        assert (rc == 0);
  
        rc = pthread_join (child, NULL);
        assert (rc == 0);
      }
  
    return NULL;
  }
  
  /* Called after the program is done counting number of spawned threads
     for a period, to compute REUSE_TIME.  */
  
  void
  after_count (void)
  {
  }
  
  /* Called after enough time has passed for TID reuse to occur.  */
  
  void
  after_reuse_time (void)
  {
  }
  
  #ifdef __linux__
  
  /* Get the running system's configured pid_max.  */
  
  static int
  linux_proc_get_pid_max (void)
  {
    static const char filename[]  ="/proc/sys/kernel/pid_max";
    FILE *file;
    char buf[100];
    int retval = -1;
  
    file = fopen (filename, "r");
    if (file == NULL)
      {
        fprintf (stderr, "unable to open %s\n", filename);
        return -1;
      }
  
    if (fgets (buf, sizeof (buf), file) != NULL)
      retval = strtol (buf, NULL, 10);
  
    fclose (file);
    return retval;
  }
  
  #endif
  
  int
  main (int argc, char *argv[])
  {
    pthread_t child;
    int rc;
    unsigned int reuse_time_raw = 0;
  
    rc = pthread_create (&child, NULL, spawner_thread_func, NULL);
    assert (rc == 0);
  
  #define COUNT_TIME 2
    sleep (COUNT_TIME);
  
  #ifdef __linux__
    tid_max = linux_proc_get_pid_max ();
  #endif
    /* If we don't know how many threads it would take to use the whole
       number space on this system, just run the test for a bit.  */
    if (tid_max > 0)
      {
        reuse_time_raw = tid_max / ((float) thread_counter / COUNT_TIME) + 0.5;
  
        /* Give it a bit more, just in case.  */
        reuse_time = reuse_time_raw + 3;
      }
  
    /* 4 seconds were sufficient on the machine this was first observed,
       an Intel i7-2620M @ 2.70GHz running Linux 3.18.7, with
       pid_max=32768.  Going forward, as machines get faster, this will
       need less time, unless pid_max is set to a very high number.  To
       avoid unreasonably long test time, cap to an upper bound.  */
    if (reuse_time > 60)
      reuse_time = 60;
    printf ("thread_counter=%lu, tid_max = %ld, reuse_time_raw=%u, reuse_time=%u\n",
  	  thread_counter, tid_max, reuse_time_raw, reuse_time);
    after_count ();
  
    sleep (reuse_time);
  
    after_reuse_time ();
    return 0;
  }
  