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+/*
+ * The MIT License
+ *
+ * Copyright (C) 2010-2017 Alexander Saprykin <saprykin.spb@gmail.com>
+ *
+ * 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.
+ */
+
+/**
+ * @file pshm.h
+ * @brief Shared memory
+ * @author Alexander Saprykin
+ *
+ * Shared memory is a memory segment which can be accessed from several threads
+ * or processes. It provides an efficient way to transfer large blocks of data
+ * between processes. It can be used as any other regular memory segment in an
+ * application.
+ *
+ * Shared memory acts like an inter-process communication method. This memory
+ * exchange implementation is process-wide so you can transfer data not only
+ * between the threads. But it makes this IPC method (actually like any other
+ * IPC method, as well) relatively heavy. Consider using other approaches
+ * instead if you do not need to cross the process boundary.
+ *
+ * A shared memory segment doesn't provide any synchronization primitives itself
+ * which means that several processes or threads can concurrently write and read
+ * from it. This can lead to data consistency problems. To avoid such situations
+ * a locking mechanism is provided: use p_shm_lock() before entering a critical
+ * section on the memory segment and p_shm_unlock() when leaving this section.
+ * The locking mechanism is working across the process boundary.
+ *
+ * A process-wide shared memory segment is identified by its name across the
+ * system, thus it is also called a named memory segment. Use p_shm_new() to
+ * open the named shared memory segment and p_shm_free() to close it.
+ *
+ * Please note the following platform specific differences:
+ *
+ * - Windows and OS/2 don't own IPC objects (processes own them), which means
+ * that a shared memory segment will be removed after the last process or thread
+ * detaches (or after terminating all the processes and threads attached to the
+ * segment) it.
+ *
+ * - UNIX systems own IPC objects. Because of that UNIX IPC objects can survive
+ * an application crash: the attached shared memory segment can contain data
+ * from the previous working session. This could happen if you have not detached
+ * from all the shared memory segments explicitly before terminating the
+ * application.
+ *
+ * - HP-UX has limitations due to its MPAS/MGAS features, so you couldn't attach
+ * to the same memory segment twice from the same process.
+ *
+ * - IRIX allows to open several instances of the same buffer within the single
+ * process, but it will close the object after the first close call from any of
+ * the threads within the process.
+ *
+ * - OpenVMS (as of 8.4 release) has broken implementation of process-wide named
+ * semaphores which leads to the broken shared memory also.
+ *
+ * - Syllable lacks support for process-wide named semaphores which leads to the
+ * absence of shared memory.
+ *
+ * - BeOS lacks support for process-wide named semaphores which leads to the
+ * absence of shared memory.
+ *
+ * You can take ownership of the shared memory segment with
+ * p_shm_take_ownership() to explicitly remove it from the system after closing.
+ */
+
+#if !defined (PLIBSYS_H_INSIDE) && !defined (PLIBSYS_COMPILATION)
+#  error "Header files shouldn't be included directly, consider using <plibsys.h> instead."
+#endif
+
+#ifndef PLIBSYS_HEADER_PSHM_H
+#define PLIBSYS_HEADER_PSHM_H
+
+#include <pmacros.h>
+#include <ptypes.h>
+#include <perror.h>
+
+P_BEGIN_DECLS
+
+/** Enum with shared memory access permissions. */
+typedef enum PShmAccessPerms_ {
+	P_SHM_ACCESS_READONLY	= 0,	/**< Read-only access.	*/
+	P_SHM_ACCESS_READWRITE	= 1	/**< Read/write access.	*/
+} PShmAccessPerms;
+
+/** Shared memory opaque data structure. */
+typedef struct PShm_ PShm;
+
+/**
+ * @brief Creates a new #PShm object.
+ * @param name Shared memory name.
+ * @param size Size of the memory segment in bytes, can't be changed later.
+ * @param perms Memory segment permissions, see #PShmAccessPerms.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Pointer to a newly created #PShm object in case of success, NULL
+ * otherwise.
+ * @since 0.0.1
+ */
+P_LIB_API PShm *	p_shm_new		(const pchar		*name,
+						 psize			size,
+						 PShmAccessPerms	perms,
+						 PError			**error);
+
+/**
+ * @brief Takes ownership of a shared memory segment.
+ * @param shm Shared memory segment.
+ * @since 0.0.1
+ *
+ * If you take ownership of the shared memory object, p_shm_free() will try to
+ * completely unlink it and remove from the system. This is useful on UNIX
+ * systems where shared memory can survive an application crash. On the Windows
+ * and OS/2 platforms this call has no effect.
+ *
+ * The common usage of this call is upon application startup to ensure that the
+ * memory segment from the previous crash will be unlinked from the system. To
+ * do that, call p_shm_new() and check if its condition is normal (the segment
+ * size, the data). If not, take ownership of the shared memory object and
+ * remove it with the p_shm_free() call. After that, create it again.
+ */
+P_LIB_API void		p_shm_take_ownership	(PShm			*shm);
+
+/**
+ * @brief Frees #PShm object.
+ * @param shm #PShm to free.
+ * @since 0.0.1
+ *
+ * It doesn't unlock a given shared memory segment, be careful to not to make a
+ * deadlock or a segfault while freeing the memory segment which is under usage.
+ */
+P_LIB_API void		p_shm_free		(PShm			*shm);
+
+/**
+ * @brief Locks #PShm object for usage.
+ * @param shm #PShm to lock.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return TRUE in case of success, FALSE otherwise.
+ * @since 0.0.1
+ *
+ * If the object is already locked then the thread will be suspended until the
+ * object becomes unlocked.
+ */
+P_LIB_API pboolean	p_shm_lock		(PShm			*shm,
+						 PError			**error);
+
+/**
+ * @brief Unlocks #PShm object.
+ * @param shm #PShm to unlock.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return TRUE in case of success, FALSE otherwise.
+ * @since 0.0.1
+ */
+P_LIB_API pboolean	p_shm_unlock		(PShm			*shm,
+						 PError			**error);
+
+/**
+ * @brief Gets a starting address of a #PShm memory segment.
+ * @param shm #PShm to get the address for.
+ * @return Pointer to the starting address in case of success, NULL otherwise.
+ * @since 0.0.1
+ */
+P_LIB_API ppointer	p_shm_get_address	(const PShm		*shm);
+
+/**
+ * @brief Gets the size of a #PShm memory segment.
+ * @param shm #PShm to get the size for.
+ * @return Size of the given memory segment in case of success, 0 otherwise.
+ * @since 0.0.1
+ *
+ * Note that the returned size would be a slightly larger than specified during
+ * the p_shm_new() call due to service information stored inside.
+ */
+P_LIB_API psize		p_shm_get_size		(const PShm		*shm);
+
+P_END_DECLS
+
+#endif /* PLIBSYS_HEADER_PSHM_H */