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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      3  * All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  *  * Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  *  * Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in
     12  *    the documentation and/or other materials provided with the
     13  *    distribution.
     14  *
     15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
     19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
     21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
     22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  */
     28 #include <pthread.h>
     29 #include <semaphore.h>
     30 #include <errno.h>
     31 #include <stdio.h>
     32 #include <time.h>
     33 #include <string.h>
     34 #include <unistd.h>
     35 
     36 /* a simple semaphore test, using three threads
     37  *
     38  *  a semaphore is initialized with a value of 1
     39  *
     40  *  Thread 1, 2 and 3 start at the same time
     41  *
     42  *  Thread 1 takes the semaphore, then sleeps for 2 seconds, then post the semaphore
     43  *  Thread 2 sleeps for 1 second, then waits the semaphore, sleeps for 2 seconds, then post the semaphoe
     44  *  Thread 3 sleeps 3 seconds, waits for the semaphore
     45  */
     46 
     47 static  sem_t   semaphore;
     48 
     49 static void*
     50 _thread1( void* unused )
     51 {
     52     printf( "thread 1: waiting for semaphore\n" );
     53     if ( sem_wait( &semaphore ) < 0 ) {
     54         printf( "thread 1: could not wait for semaphore: %s\n", strerror(errno) );
     55         return NULL;
     56     }
     57     printf( "thread 1: got the semaphore ! sleeping for 2 seconds\n" );
     58     sleep( 2 );
     59     printf( "thread 1: awake !! posting semaphore\n" );
     60     if ( sem_post( &semaphore ) < 0 ) {
     61         printf( "thread 2: could not post semaphore: %s\n", strerror(errno) );
     62     }
     63     printf( "thread 1: quitting\n" );
     64     return NULL;
     65 }
     66 
     67 static void*
     68 _thread2( void* unused )
     69 {
     70     printf( "thread 2: sleeping for 1 second\n" );
     71     sleep(1);
     72     printf( "thread 2: awake !! waiting for semaphore\n" );
     73     if ( sem_wait( &semaphore ) < 0 ) {
     74         printf( "thread 2: could not wait for semaphore: %s\n", strerror(errno) );
     75         return NULL;
     76     }
     77     printf( "thread 2: got the semaphore ! sleeping for 2 seconds\n" );
     78     sleep( 2 );
     79     printf( "thread 2: awake !! posting semaphore\n" );
     80     if ( sem_post( &semaphore ) < 0 ) {
     81         printf( "thread 2: could not post semaphore: %s\n", strerror(errno) );
     82     }
     83     printf( "thread 2: quitting\n" );
     84     return NULL;
     85 }
     86 
     87 
     88 static void*
     89 _thread3( void* unused )
     90 {
     91     printf( "thread 3: sleeping for 3 seconds\n" );
     92     sleep(3);
     93     printf( "thread 3: awake !! waiting for semaphore\n" );
     94     if ( sem_wait( &semaphore ) < 0 ) {
     95         printf( "thread 3: could not wait for semaphore: %s\n", strerror(errno) );
     96         return NULL;
     97     }
     98     printf( "thread 3: got semaphore. quitting\n" );
     99     return NULL;
    100 }
    101 
    102 typedef void*  (*thread_func)(void*);
    103 
    104 static const  thread_func  thread_routines[] =
    105 {
    106     &_thread1,
    107     &_thread2,
    108     &_thread3
    109 };
    110 
    111 int  main( void )
    112 {
    113     pthread_t   t[3];
    114     int         nn;
    115 
    116     if ( sem_init( &semaphore, 0, 1 ) < 0 ) {
    117         printf( "could not initialize semaphore: %s\n", strerror(errno) );
    118         return -1;
    119     }
    120 
    121     for ( nn = 0; nn < 3; nn++ ) {
    122         if ( pthread_create( &t[nn], NULL, thread_routines[nn], NULL ) < 0 ) {
    123             printf("could not create thread %d: %s\n", nn+1, strerror(errno) );
    124             return -2;
    125         }
    126     }
    127     sleep( 5 );
    128     return 0;
    129 }
    130