pthread_mutex_lock gets stuck - c

Question

The revelant code may be found here: http://pastebin.com/VbhtQckm
The problem is at line
85. pthread_mutex_lock(ID_retrieval_pool->info->lock);
I'm running the server and it's getting stuck at lock. The memory is allocated, I'm initializing the mutex and it's the only thread who's owning that shared memory.
I did debug with GDB and Valgrind using helgrind tool but did not find any clue.
Possible problems which think may cause this:
mutex is not being initialized (I'm using a block is shared memory which I'm initializing as a mutex);
deadlock? in the man page https://www.sourceware.org/pthreads-
win32/manual/pthread_mutex_init.html says this can cause this;
Please note that this code is for learning purpose.
Edit, the code is:
// common_header.h + common_header.c
#ifndef DATA_TYPES_H
#define DATA_TYPES_H
#include <pthread.h>
#include <errno.h>
#define RETREIVE_ID_KEY 1
typedef enum {
SHM_State_None,
SHM_State_ID_Available,
SHM_State_ID_Not_Available,
} SHM_State;
typedef struct {
pthread_mutex_t *lock; // locked if any thread is modifying data
SHM_State state;
} data_state;
typedef int shmid_t;
typedef struct data_pool {
data_state *info;
shmid_t shm_id;
} data_pool;
// other data structures
extern data_state * data_state_initialize_by_setting_address(void *address)
{
data_state *data = (data_state *)address;
data->lock = (pthread_mutex_t *)address;
pthread_mutex_init(data->lock, NULL);
data->state = SHM_State_None;
return data;
}
extern data_pool * data_pool_initialize_by_setting_address(void *address)
{
data_pool *data = (data_pool *)address;
data->info = data_state_initialize_by_setting_address(address);
data->shm_id = 0; // invalid though, the structure's client has to set a valid one
return data;
}
// other initialization functions
#endif // DATA_TYPES_H
///----------------------------------------------------------------------------------------\\\
// main.c -- Server
#include "common_header.h"
#define SHM_INVALID_ADDRESS (void *)-1
#define SHMGET_RW_FLAGS 0666
#define SHMAT_RW_FLAGS 0
bool initialize_data();
static data_pool *ID_retrieval_pool = NULL;
int main(int argc, char *argv[])
{
if (!initialize_data()) {
return EXIT_FAILURE;
}
// Do other stuff
return EXIT_SUCCESS;
}
bool initialize_data()
{
// some irrelevant initialization code
shmid_t shm_ID = shmget(RETREIVE_ID_KEY,
sizeof(data_pool),
IPC_CREAT | SHMGET_RW_FLAGS);
void *shm_address = shmat(shm_ID, NULL, SHMAT_RW_FLAGS);
if (shm_address == SHM_INVALID_ADDRESS) {
return false;
}
ID_retrieval_pool = data_pool_initialize_by_setting_address(shm_address);
pthread_mutex_lock(ID_retrieval_pool->info->lock);
ID_retrieval_pool->shm_id = get_shared_ID();
ID_retrieval_pool->info->state = SHM_State_ID_Available;
pthread_mutex_unlock(ID_retrieval_pool->info->lock);
// other initialization code
return true;
}

Answer 1

You have an interesting and incorrect way of initializing the mutex:
data->lock = (pthread_mutex_t *)address; /* address == &data */
pthread_mutex_init(data->lock, NULL);
In your code address is the address of the outer struct: this does not actually allocate a usable block of memory.
I suggest you just make the mutex non-pointer and then initialize it:
/* In the struct. */
pthread_mutex_t lock;
/* In your function. */
pthread_mutex_init(&data->lock, NULL);