linux-lock.c

来自「wm PNE 3.3 source code, running at more 」· C语言 代码 · 共 112 行

/* -------------------------------------------------------------------------- */
/*                                                                            */
/* Filename: linux-lock.c                                                     */
/*                                                                            */
/* Author:   Icon Laboratories, Inc.                                          */
/*           [phone]                                                   */
/*           http://www.icon-labs.com                                         */
/*                                                                            */
/* Notice:   Copyright 2001, Icon Laboratories, Inc.  All rights reserved.    */
/*                                                                            */
/* Description: This file contains common functions for MIB-2 Agent           */
/*              based on WindRiver's Envoy/Emissary tools.                    */
/*                                                                            */
/* Modification History:                                                      */
/*                                                                            */
/* Jim Jones   v1.2    07-20-01    Removed explicit include for envoy.h       */
/* Jim Jones   v1.1    04-23-01    Recompiled for Envoy v9.1                  */
/*                                                                            */
/* -------------------------------------------------------------------------- */
/* this is the lock implementation for Linux.  It uses two pthread
 * mutexes to implement the classic solution to the reader-
 * writers problem.  It favors readers over writers.  There are 
 * other solutions that favor writers over readers.  See, for 
 * example: 
 *  http://www.coe.neu.edu/~signoril/op_sys/readwriters.html
 *  http://www.cs.bc.edu/~mc362/readwriters.html
 *        or, for more general info:
 *  http://rtlab.kaist.ac.kr/~sikang/sim/rw.html
 */

#include <wrn/wm/snmp/engine/asn1conf.h>
#include <wrn/wm/snmp/engine/asn1.h>
#include <wrn/wm/snmp/engine/buffer.h>
#include <wrn/wm/snmp/engine/mib.h>
#include <wrn/wm/snmp/engine/localio.h>
#include <wrn/wm/snmp/engine/snmpdefs.h>
#include <wrn/wm/snmp/engine/snmp.h>
#include <wrn/wm/snmp/engine/auxfuncs.h>
#include <stdio.h>
#include <errno.h>

#if (INSTALL_ENVOY_SNMP_LOCK)

int reader_lock(ENVOY_LOCK_T *lock)
{
  /* lock the reader mutex */
  if ( pthread_mutex_lock( &(lock->reader) ) )
    return -1;

  /* increment the readers count */
  lock->nreaders++;
  
  /* if readers count == 1, meaning this is the first reader,
   * lock the writers lock */
  if ( lock->nreaders == 1 )
  {
    if ( pthread_mutex_lock( &(lock->writer) ) )
      return -1;
  }

  /* release the reader lock */
  if ( pthread_mutex_unlock( &(lock->reader) ) )
    return -1;

  return 0;
}


int reader_unlock(ENVOY_LOCK_T *lock)
{
  /* lock the reader mutex */
  if ( pthread_mutex_lock( &(lock->reader) ) )
    return -1;

  /* decrement the readers count */
  lock->nreaders--;

  /* if readers count == 0, meaning this is the last reader,
   * unlock the writers lock */
  if ( lock->nreaders == 0 )
  {
    if ( pthread_mutex_unlock( &(lock->writer) ) )
      return -1;
  }

  /* release the reader lock */
  if ( pthread_mutex_unlock( &(lock->reader) ) )
    return -1;

  return 0;
}


int writer_lock(ENVOY_LOCK_T *lock)
{
  if ( pthread_mutex_lock( &(lock->writer) ) )
    return -1;

  return 0;
}


int writer_unlock(ENVOY_LOCK_T *lock)
{
  if ( pthread_mutex_unlock( &(lock->writer) ) )
    return -1;
    
  return 0;
}

#endif