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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 pshmbuffer.h
+ * @brief Shared memory buffer
+ * @author Alexander Saprykin
+ *
+ * A shared memory buffer works like any other buffer but it is built upon a
+ * shared memory region instead of the process-only address space. Thus it
+ * inherits all the advantages and disadvantages of shared memory behavior. You
+ * should read about #PShm before using this buffer implementation to understand
+ * underlying restrictions.
+ *
+ * The shared memory buffer is process-wide and identified by its name across
+ * the system, thus it can be opened by any process if it knows its name. Use
+ * p_shm_buffer_new() to open the shared memory buffer and p_shm_buffer_free()
+ * to close it.
+ *
+ * All read/write operations are completely thread- and process-safe, which
+ * means that no other synchronization primitive is required, even for inter-
+ * process access. A #PShm locking mechanism is used for access synchronization.
+ *
+ * The buffer is cyclic and non-overridable which means that you wouldn't get
+ * buffer overflow and wouldn't override previously written data until reading
+ * it.
+ *
+ * The read operation checks whether there is any data available and reads it in
+ * case of successful check. After reading the data used space in the buffer is
+ * marked as free and any subsequent write operation may overwrite it. Thus you
+ * couldn't read the same data twice. The read operation is performed with the
+ * p_shm_buffer_read() call.
+ *
+ * The write operation checks whether there is enough free space available and
+ * writes a given memory block only if the buffer has enough free space.
+ * Otherwise no data is written. The write operation is performed with the
+ * p_shm_buffer_write() call.
+ *
+ * Data can be read and written into the buffer only sequentially. There is no
+ * way to access an arbitrary address inside the buffer.
+ *
+ * You can take ownership of the shared memory buffer with
+ * p_shm_buffer_take_ownership() to explicitly remove it from the system after
+ * closing. Please refer to the #PShm description to understand the intention of
+ * this action.
+ */
+
+#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_PSHMBUFFER_H
+#define PLIBSYS_HEADER_PSHMBUFFER_H
+
+#include <ptypes.h>
+#include <pmacros.h>
+#include <perror.h>
+
+P_BEGIN_DECLS
+
+/** Shared memory buffer opaque data structure. */
+typedef struct PShmBuffer_ PShmBuffer;
+
+/**
+ * @brief Creates a new #PShmBuffer structure.
+ * @param name Unique buffer name.
+ * @param size Buffer size in bytes, can't be changed later.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Pointer to the #PShmBuffer structure in case of success, NULL
+ * otherwise.
+ * @since 0.0.1
+ *
+ * If a buffer with the same name already exists then the @a size will be
+ * ignored and the existing buffer will be returned.
+ */
+P_LIB_API PShmBuffer *	p_shm_buffer_new		(const pchar	*name,
+							 psize		size,
+							 PError		**error);
+
+/**
+ * @brief Frees #PShmBuffer structure.
+ * @param buf #PShmBuffer to free.
+ * @since 0.0.1
+ *
+ * Note that a buffer will be completely removed from the system only after the
+ * last instance of the buffer with the same name is closed.
+ */
+P_LIB_API void		p_shm_buffer_free		(PShmBuffer	*buf);
+
+/**
+ * @brief Takes ownership of a shared memory buffer.
+ * @param buf Shared memory buffer.
+ * @since 0.0.1
+ *
+ * If you take ownership of the shared memory buffer, p_shm_buffer_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 can be removed from the system. To do
+ * that, call p_shm_buffer_new() and check if its condition is normal (used
+ * space, free space). If not, take ownership of the shared memory buffer object
+ * and remove it with the p_shm_buffer_free() call. After that, create it again.
+ */
+P_LIB_API void		p_shm_buffer_take_ownership	(PShmBuffer	*buf);
+
+/**
+ * @brief Tries to read data from a shared memory buffer.
+ * @param buf #PShmBuffer to read data from.
+ * @param[out] storage Output buffer to put data in.
+ * @param len Storage size in bytes.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Number of read bytes (can be 0 if buffer is empty), or -1 if error
+ * occured.
+ * @since 0.0.1
+ */
+P_LIB_API pint		p_shm_buffer_read		(PShmBuffer	*buf,
+							 ppointer	storage,
+							 psize		len,
+							 PError		**error);
+
+/**
+ * @brief Tries to write data into a shared memory buffer.
+ * @param buf #PShmBuffer to write data into.
+ * @param data Data to write.
+ * @param len Data size in bytes.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Number of written bytes (can be 0 if buffer is full), or -1 if error
+ * occured.
+ * @since 0.0.1
+ * @note Write operation is performed only if the buffer has enough space for
+ * the given data size.
+ */
+P_LIB_API pssize	p_shm_buffer_write		(PShmBuffer	*buf,
+							 ppointer	data,
+							 psize		len,
+							 PError		**error);
+
+/**
+ * @brief Gets free space in the shared memory buffer.
+ * @param buf #PShmBuffer to check space in.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Free space in bytes in case of success, -1 otherwise.
+ * @since 0.0.1
+ */
+P_LIB_API pssize	p_shm_buffer_get_free_space	(PShmBuffer	*buf,
+							 PError		**error);
+
+/**
+ * @brief Gets used space in the shared memory buffer.
+ * @param buf #PShmBuffer to check space in.
+ * @param[out] error Error report object, NULL to ignore.
+ * @return Used space in bytes in case of success, -1 otherwise.
+ * @since 0.0.1
+ */
+P_LIB_API pssize	p_shm_buffer_get_used_space	(PShmBuffer	*buf,
+							 PError		**error);
+
+/**
+ * @brief Clears all data in the buffer and fills it with zeros.
+ * @param buf #PShmBuffer to clear.
+ * @since 0.0.1
+ */
+P_LIB_API void		p_shm_buffer_clear		(PShmBuffer	*buf);
+
+P_END_DECLS
+
+#endif /* PLIBSYS_HEADER_PSHMBUFFER_H */