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126 lines
5.3 KiB
C++
126 lines
5.3 KiB
C++
/** Shared-memory interface: The interface functions that the external program should use.
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*
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* @file
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* @author Georg Martin Reinke <georg.reinke@rwth-aachen.de>
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* @copyright 2014-2020, Institute for Automation of Complex Power Systems, EONERC
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* @license GNU General Public License (version 3)
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*
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* VILLASnode
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*********************************************************************************/
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/** Interface to the shared memory node for external programs.
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*
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* @addtogroup shmem Shared memory interface
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* @{
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*/
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#pragma once
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#include <villas/pool.h>
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#include <villas/queue.h>
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#include <villas/queue_signalled.h>
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#include <villas/sample.h>
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#define DEFAULT_SHMEM_QUEUELEN 512u
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#define DEFAULT_SHMEM_SAMPLELEN 64u
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/** Struct containing all parameters that need to be known when creating a new
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* shared memory object. */
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struct shmem_conf {
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int polling; /**< Whether to use polling instead of POSIX CVs */
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int queuelen; /**< Size of the queues (in elements) */
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int samplelen; /**< Maximum number of data entries in a single sample */
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};
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/** The structure that actually resides in the shared memory. */
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struct shmem_shared {
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int polling; /**< Whether to use a pthread_cond_t to signal if new samples are written to incoming queue. */
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struct queue_signalled queue; /**< Queue for samples passed in both directions. */
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struct pool pool; /**< Pool for the samples in the queues. */
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};
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/** Relevant information for one direction of the interface. */
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struct shmem_dir {
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void *base; /**< Base address of the region. */
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const char *name; /**< Name of the shmem object. */
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size_t len; /**< Total size of the region. */
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struct shmem_shared *shared; /**< Actually shared datastructure */
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};
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/** Main structure representing the shared memory interface. */
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struct shmem_int {
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struct shmem_dir read, write;
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std::atomic<int> readers, writers, closed;
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};
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/** Open the shared memory objects and retrieve / initialize the shared data structures.
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* Blocks until another process connects by opening the same objects.
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*
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* @param[in] wname Name of the POSIX shared memory object containing the output queue.
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* @param[in] rname Name of the POSIX shared memory object containing the input queue.
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* @param[inout] shm The shmem_int structure that should be used for following
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* calls will be written to this pointer.
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* @param[in] conf Configuration parameters for the output queue.
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* @retval 0 The objects were opened and initialized successfully.
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* @retval <0 An error occured; errno is set accordingly.
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*/
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int shmem_int_open(const char* wname, const char* rname, struct shmem_int* shm, struct shmem_conf* conf);
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/** Close and destroy the shared memory interface and related structures.
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*
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* @param shm The shared memory interface.
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* @retval 0 Closing successfull.
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* @retval <0 An error occurred; errno is set appropiately.
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*/
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int shmem_int_close(struct shmem_int *shm);
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/** Read samples from the interface.
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*
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* @param shm The shared memory interface.
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* @param smps An array where the pointers to the samples will be written. The samples
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* must be freed with sample_decref after use.
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* @param cnt Number of samples to be read.
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* @retval >=0 Number of samples that were read. Can be less than cnt (including 0) in case not enough samples were available.
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* @retval -1 The other process closed the interface; no samples can be read anymore.
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*/
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int shmem_int_read(struct shmem_int *shm, struct sample * const smps[], unsigned cnt);
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/** Write samples to the interface.
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*
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* @param shm The shared memory interface.
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* @param smps The samples to be written. Must be allocated from shm_int_alloc.
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* @param cnt Number of samples to write.
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* @retval >=0 Number of samples that were successfully written. Can be less than cnt (including 0) in case of a full queue.
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* @retval -1 The write failed for some reason; no more samples can be written.
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*/
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int shmem_int_write(struct shmem_int *shm, const struct sample * const smps[], unsigned cnt);
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/** Allocate samples to be written to the interface.
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*
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* The writing process must not free the samples; only the receiving process should free them using sample_decref after use.
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* @param shm The shared memory interface.
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* @param smps Array where pointers to newly allocated samples will be returned.
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* @param cnt Number of samples to allocate.
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* @return Number of samples that were successfully allocated (may be less then cnt).
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*/
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int shmem_int_alloc(struct shmem_int *shm, struct sample *smps[], unsigned cnt);
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/** Returns the total size of the shared memory region with the given size of
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* the input/output queues (in elements) and the given number of data elements
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* per struct sample. */
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size_t shmem_total_size(int queuelen, int samplelen);
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/** @} */
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