/*
Modifications Copyright © 2019 – 2020 Advanced Micro Devices, Inc. All Rights
Reserved.
Copyright (c) 2018 Oleg Yamnikov

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

#ifndef SRC_SHARED_MUTEX_SHARED_MUTEX_H_
#define SRC_SHARED_MUTEX_SHARED_MUTEX_H_

#include <sys/stat.h>

#include <pthread.h>  // pthread_mutex_t, pthread_mutexattr_t,
                      // pthread_mutexattr_init, pthread_mutexattr_setpshared,
                      // pthread_mutex_init, pthread_mutex_destroy

// Structure of a shared mutex.
typedef struct shared_mutex_t {
  pthread_mutex_t *ptr;  // Pointer to the pthread mutex and
                         // shared memory segment.
  int shm_fd;            // Descriptor of shared memory object.
  char* name;            // Name of the mutex and associated
                         // shared memory object.
  int created;           // Equals 1 (true) if initialization
                         // of this structure caused creation
                         // of a new shared mutex.
                         // Equals 0 (false) if this mutex was
                         // just retrieved from shared memory.
} shared_mutex_t;

// Initialize a new shared mutex with given `name`. If a mutex
// with such name exists in the system, it will be loaded.
// Otherwise a new mutes will by created.
//
// In case of any error, it will be printed into the standard output
// and the returned structure will have `ptr` equal `NULL`.
// `errno` wil not be reset in such case, so you may used it.
//
// **NOTE:** In case when the mutex appears to be uncreated,
// this function becomes *non-thread-safe*. If multiple threads
// call it at one moment, there occur several race conditions,
// in which one call might recreate another's shared memory
// object or rewrite another's pthread mutex in the shared memory.
// There is no workaround currently, except to run first
// initialization only before multi-threaded or multi-process
// functionality.
shared_mutex_t shared_mutex_init(const char *name, mode_t mode, bool retried=false);

// Close access to the shared mutex and free all the resources,
// used by the structure.
//
// Returns 0 in case of success. If any error occurs, it will be
// printed into the standard output and the function will return -1.
// `errno` wil not be reset in such case, so you may used it.
//
// **NOTE:** It will not destroy the mutex. The mutex would not
// only be available to other processes using it right now,
// but also to any process which might want to use it later on.
// For complete desctruction use `shared_mutex_destroy` instead.
//
// **NOTE:** It will not unlock locked mutex.
int shared_mutex_close(shared_mutex_t mutex);

// Close and destroy shared mutex.
// Any open pointers to it will be invalidated.
//
// Returns 0 in case of success. If any error occurs, it will be
// printed into the standard output and the function will return -1.
// `errno` wil not be reset in such case, so you may used it.
//
// **NOTE:** It will not unlock locked mutex.
int shared_mutex_destroy(shared_mutex_t mutex);

#endif  // SRC_SHARED_MUTEX_SHARED_MUTEX_H_