shm_lock.h

#ifndef shm_locks_h_
#define shm_locks_h_

#include <pthread.h>
#include <stdint.h>

// Magic number to ensure we open the right SHM segment
#define MAGIC 0x87D1

#ifdef __cplusplus
extern "C" {
#endif

// Type for our bitmaps
typedef uint32_t bitmap_t;

// bitmap size
#define BITMAP_SIZE (sizeof(bitmap_t) * 8)

// Struct to hold a single bitmap and associated locks
typedef struct lock_group {
    bitmap_t        bitmap;
    pthread_mutex_t locks[BITMAP_SIZE];
} lock_group_t;

// Struct to hold our SHM locks.
// Unused is required to be 0 in the current implementation. If we ever make
// changes to this structure in the future, this will be repurposed as a version
// field.
typedef struct shm_struct {
    uint16_t        magic;
    uint16_t        unused;
    pthread_mutex_t segment_lock;
    uint32_t        num_bitmaps;
    uint32_t        num_locks;
    lock_group_t    locks[];
} shm_struct_t;

shm_struct_t *setup_lock_shm(char *path, uint32_t num_locks, int *error_code);
shm_struct_t *open_lock_shm(char *path, uint32_t num_locks, int *error_code);
int32_t close_lock_shm(shm_struct_t *shm);
int64_t allocate_semaphore(shm_struct_t *shm);
int32_t allocate_given_semaphore(shm_struct_t *shm, uint32_t sem_index);
int32_t deallocate_semaphore(shm_struct_t *shm, uint32_t sem_index);
int32_t deallocate_all_semaphores(shm_struct_t *shm);
int32_t lock_semaphore(shm_struct_t *shm, uint32_t sem_index);
int32_t unlock_semaphore(shm_struct_t *shm, uint32_t sem_index);

#ifdef __cplusplus
}
#endif

#endif