/** \brief Locks the semaphore only after it is unlocked by another process.
* \param sem_set_id The semaphore handle that you want to lock. */
static void
ketama_sem_safely_lock( int sem_set_id )
{
int sanity = 0;
while ( semctl( sem_set_id, 0, GETVAL, 0 ) == 2 )
{
// wait for the continuum creator to finish, but don't block others
usleep( 5 );
// if we are waiting for > 1 second, take drastic action:
if(++sanity > 200000)
{
usleep( rand()%50000 );
ketama_sem_unlock( sem_set_id );
break;
}
}
ketama_sem_lock( sem_set_id );
}
int
ketama_roll( ketama_continuum* contptr, char* filename )
{
strcpy( k_error, "" );
key_t key;
int shmid;
int *data;
int sem_set_id;
// setlogmask( LOG_UPTO ( LOG_NOTICE | LOG_ERR | LOG_INFO ) );
// openlog( "ketama", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1 );
key = ftok( filename, 'R' );
if ( key == -1 )
{
sprintf( k_error, "Invalid filename specified: %s", filename );
return 0;
}
*contptr = malloc( sizeof( continuum ) );
(*contptr)->numpoints = 0;
(*contptr)->array = 0;
(*contptr)->modtime = 0;
sem_set_id = ketama_sem_init( key );
int sanity = 0;
while ( semctl( sem_set_id, 0, GETVAL, 0 ) == 2 )
{
// wait for the continuum creator to finish, but don't block others
usleep( 5 );
// if we are waiting for > 1 second, take drastic action:
if(++sanity > 1000000)
{
usleep( rand()%50000 );
ketama_sem_unlock( sem_set_id );
break;
}
}
time_t modtime = file_modtime( filename );
time_t* fmodtime = 0;
while ( !fmodtime || modtime != *fmodtime )
{
shmid = shmget( key, MC_SHMSIZE, 0 ); // read only attempt.
data = shmat( shmid, (void *)0, SHM_RDONLY );
if ( data == (void *)(-1) || (*contptr)->modtime != 0 )
{
ketama_sem_lock( sem_set_id );
// if ( (*contptr)->modtime == 0 )
// syslog( LOG_INFO, "Shared memory empty, creating and populating...\n" );
// else
// syslog( LOG_INFO, "Server definitions changed, reloading...\n" );
if ( !ketama_create_continuum( key, filename ) )
{
// strcpy( k_error, "Ketama_create_continuum() failed!" );
ketama_sem_unlock( sem_set_id );
return 0;
}
/* else
syslog( LOG_INFO, "ketama_create_continuum() successfully finished.\n" );*/
shmid = shmget( key, MC_SHMSIZE, 0 ); // read only attempt.
data = shmat( shmid, (void *)0, SHM_RDONLY );
ketama_sem_unlock( sem_set_id );
}
if ( data == (void *)(-1) )
{
strcpy( k_error, "Failed miserably to get pointer to shmemdata!" );
return 0;
}
(*contptr)->numpoints = *data;
(*contptr)->modtime = ++data;
(*contptr)->array = data + sizeof( void* );
fmodtime = (time_t*)( (*contptr)->modtime );
}
return 1;
}