1/* 2 Buffer. Very fast reblocking filter speedy writing of tapes. 3 Copyright (C) 1990,1991 Lee McLoughlin 4 5 This program is free software; you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 1, or (at your option) 8 any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 GNU General Public License for more details. 14 15 You should have received a copy of the GNU General Public License 16 along with this program; if not, write to the Free Software 17 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 18 19 Lee McLoughlin. 20 Dept of Computing, Imperial College, 21 180 Queens Gate, London, SW7 2BZ, UK. 22 23 Email: L.McLoughlin@doc.ic.ac.uk 24*/ 25 26/* This is a simple module to provide an easier to understand interface to 27 * semaphores */ 28 29#include <stdio.h> 30#include <sys/types.h> 31#include <sys/stat.h> 32#include <sys/ipc.h> 33#include <sys/sem.h> 34#include <errno.h> 35#include "sem.h" 36 37#if defined(SYS5) || defined(ultrix) || defined(_AIX) 38union semun { 39 int val; 40 struct semid_ds *buf; 41 ushort *array; 42}; 43#endif 44 45/* IMPORTS */ 46 47/* Used to print error messages */ 48extern void report_proc(); 49 50/* Used to end the program - on error */ 51extern void byee(); 52 53 54 55/* Set a semaphore to a particular value - meant to be used before 56 * first lock/unlock */ 57void 58sem_set( sem_id, semn, val ) 59 int sem_id; 60 int semn; 61 int val; 62{ 63 union semun arg; 64 extern int errno; 65 66 arg.val = val; 67 68 errno = 0; 69 semctl( sem_id, semn, SETVAL, arg ); 70 if( errno != 0 ){ 71 report_proc(); 72 perror( "internal error, sem_set" ); 73 byee( -1 ); 74 } 75} 76 77int 78new_sems( nsems ) 79 int nsems; 80{ 81 int sem; 82 int i; 83 84 sem = semget( IPC_PRIVATE, nsems, IPC_CREAT|S_IREAD|S_IWRITE ); 85 if( sem < 0 ){ 86 report_proc(); 87 perror( "internal error, couldn't create semaphore" ); 88 byee( -1 ); 89 } 90 91 for( i = 0; i < nsems; i++ ){ 92 sem_set( sem, i, 1 ); 93 } 94 95 return sem; 96} 97 98static 99do_sem( sem_id, pbuf, err ) 100 int sem_id; 101 struct sembuf *pbuf; 102 char *err; 103{ 104 /* This just keeps us going in case of EINTR */ 105 while( 1 ){ 106 if( semop( sem_id, pbuf, 1 ) == -1 ){ 107 if( errno == EINTR ){ 108 continue; 109 } 110 report_proc(); 111 fprintf( stderr, "internal error pid %d, lock id %d\n", 112 getpid(), sem_id ); 113 perror( err ); 114 byee( -1 ); 115 } 116 return; 117 } 118} 119 120void 121lock( sem_id, semn ) 122 int sem_id; 123 int semn; 124{ 125 struct sembuf sembuf; 126 127 sembuf.sem_num = semn; 128 sembuf.sem_op = -1; 129 sembuf.sem_flg = 0; 130 131 do_sem( sem_id, &sembuf, "lock error" ); 132} 133 134void 135unlock( sem_id, semn ) 136 int sem_id; 137 int semn; 138{ 139 struct sembuf sembuf; 140 141 sembuf.sem_num = semn; 142 sembuf.sem_op = 1; 143 sembuf.sem_flg = 0; 144 145 do_sem( sem_id, &sembuf, "unlock error" ); 146} 147 148void 149remove_sems( sem_id ) 150 int sem_id; 151{ 152 if( sem_id == -1 ) 153 return; 154 155 if( semctl( sem_id, 0, IPC_RMID, NULL ) == -1 ){ 156 report_proc(); 157 perror( "internal error, failed to remove semaphore" ); 158 } 159} 160