Hi!
I'm writting an application that uses shared memory and semaphores in PHP
and C/C++. PHP script writes data in memory and the C program read it. I
have no problems with the PHP script, but I can not acquire semaphores with
C/C++.
So, I wrote a sample program to test the semaphores. It's supposed to
acquire the semaphore and keep it blocked, but it does not. I have no
previous experience in Unix programming and I based my code in php source
code (sysvsem.c). I appreciate you if you can help me to solve my problem.
This is the sample program:
//
// gcc recolector.c -o recolector
//
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <errno.h>
#include "structure.h"
#include "mysql.h"
//
#define PERMS S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH
// Los 3 semáforos que PHP utiliza.
#define SYSVSEM_SEM 0 // Semáforo actual
#define SYSVSEM_USAGE 1
#define SYSVSEM_SETVAL 2
union semun {
int val; /* value for SETVAL */
struct semid_ds *buf; /* buffer for IPC_STAT, IPC_SET */
unsigned short int *array; /* array for GETALL, SETALL */
struct seminfo *__buf; /* buffer for IPC_INFO */
};
void main( void ) {
int shmid;
key_t key = 4096;
char *shm, *s;
if ( ( shmid = shmget(key, 27, 0666) ) < 0 ) {
perror("shmget");
exit(1);
}
// Get/create the semaphore
int semid = semget( key, 3, PERMS | IPC_CREAT );
if ( semid == -1 ) {
perror("No pudo crear el semáforo");
exit(1);
}
struct sembuf sop[3];
/* Wait for sem 1 to be zero . . . */
sop[0].sem_num = SYSVSEM_SETVAL;
sop[0].sem_op = 0;
sop[0].sem_flg = 0;
/* . . . and increment it so it becomes non-zero . . . */
sop[1].sem_num = SYSVSEM_SETVAL;
sop[1].sem_op = 1;
sop[1].sem_flg = SEM_UNDO;
/* . . . and increment the usage count. */
sop[2].sem_num = SYSVSEM_USAGE;
sop[2].sem_op = 1;
sop[2].sem_flg = SEM_UNDO;
while ( semop(semid, sop, 3) == -1 ) {
if ( errno != EINTR ) {
printf( "semop() failed acquiring SYSVSEM_SETVAL for key 0x%x:
%s", key, strerror(errno));
exit(1);
}
}
union semun un;
int count = semctl(semid, SYSVSEM_USAGE, GETVAL, un );
if ( count == -1 ) {
printf( "semctl() failed acquiring SYSVSEM_USAGE for key 0x%x: %s",
key, strerror(errno));
exit(1);
}
if (count == 1) {
union semun semarg;
semarg.val = 1;
if (semctl(semid, SYSVSEM_SEM, SETVAL, semarg) == -1) {
printf( "semctl(SETVAL) failed for key %0x%x: %s", key,
strerror(errno));
exit(1);
}
}
/* Set semaphore 1 back to zero. */
sop[0].sem_num = SYSVSEM_SETVAL;
sop[0].sem_op = -1;
sop[0].sem_flg = SEM_UNDO;
while (semop(semid, sop, 1) == -1) {
if (errno != EINTR) {
printf( "semop() failed releasing SYSVSEM" );
exit(1);
}
}
// sem_ptr = (sysvsem_sem *) emalloc(sizeof(sysvsem_sem));
// sem_ptr->key = key;
//
sop[0].sem_num = SYSVSEM_SEM;
sop[0].sem_op = -1;
sop[0].sem_flg = SEM_UNDO;
while ( semop( semid, sop, 1 ) == -1) {
if (errno != EINTR) {
printf( "semop(acquire) failed for key 0x%x: %sx: %s", key,
strerror(errno) );
exit(1);
}
}
//
if ((shm = (char *) shmat(shmid, NULL, 0)) == (char *) -1) {
perror("shmat");
exit(1);
}
// Ciclo principal
/*
while ( true ) {
for (s = shm; *s != NULL; s++)
putchar(*s);
putchar('\n');
usleep(1000000L);
}
*/
exit(0);
}
Thanks
Jorge Machin
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