weShareMem.h File Reference

One chunk of shared memory on a Raspberry Pi. More...

#include "weUtil.h"
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/sem.h>
#include <errno.h>

Data Structures
union	semCtlPar_t
	Parameter type for semctl(). More...

Macros
#define	ANZ_SEMAS
	Standard semaphore set size. More...
#define	PERM
	access rights
#define	SEMAPHORE_KEY
	Semaphore unique key "KÇÏfig25".
#define	SHARED_MEMORY_KEY
	Shared memory key "Buffer25".
#define	SHARED_MEMORY_SIZE
	Sweet home control (meterPi) shared memory size. More...

Functions
int	deleteSemas ()
	Delete the one semaphore set. More...
int	deleteSharedMem ()
	Delete and detach the shared memory. More...
int	detachSharedMem ()
	Detach the shared memory.
int	getSemas ()
	Get the one semaphore set. More...
int	initialiseSemas ()
	Initialise the one semaphore set. More...
void *	initialiseSharedMem ()
	Initialise shared memory. More...
int	semaphoreClt (int const semNum, int const op, semCtlPar_t par)
	Control semaphores of the set. More...
int	semaphoreLock (int const semNum, int ms)
	Lock one semaphore of the set. More...
int	semaphoreOperation (int const semNum, int const op, int ms)
	Operation on one semaphore of the set. More...
int	semaphoreUnlock (int const semNum)
	Unlock one semaphore of the set. More...

Variables
int	shMemErrno
	Last error number of (some ) semaphore operations. More...
int	shMemSem
	Semaphore set identifier. More...
const semCtlPar_t	VAL0
	value 0 for SETVAL
const semCtlPar_t	VAL1
	value 1 for SETVAL
const semCtlPar_t	VAL9
	value 9 for SETVAL

Detailed Description

One chunk of shared memory on a Raspberry Pi.

Copyright  (c)  2018  2025   Albrecht Weinert
weinert-automation.de            a-weinert.de
 
    /         /      /\
   /         /___   /  \      |
   \        /____\ /____\ |  _|__
    \  /\  / \    /      \|   |
     \/  \/   \__/        \__/|_                                 

Revision history

Rev. 76 26.02.2025
Rev.  80  11.11.2017 : new
Rev. 175  28.07.2018 : beauty
Rev. 191  15.02.2019 : minor comment text changes
Rev. 270  03.11.2024 : semphore set & shared memory defined here, only!
Rev.  76  24.02.2025 : clarification of 64 bit OS malfunction

Provide one piece of shared memory to be used by multiple programs on one Pi, e.g. one process control program range and few (cgi) programs for (human) observation and control.

Macro Definition Documentation

ANZ_SEMAS

#define ANZ_SEMAS

Standard semaphore set size.

Standard semaphore set of three (3..10)

Usually three (3..10)

SHARED_MEMORY_SIZE

#define SHARED_MEMORY_SIZE

Sweet home control (meterPi) shared memory size.

It is 1K. 512 byte would be enough, but shared memory segments will probably come as multiples of PAGE_SIZE. With meterPi (32bit Raspbian) and growPi (64bit) the values are 4096.
Get the page size by /code meterPi:~ $getconf PAGE_SIZE 4096 /endcode

Function Documentation

getSemas()

int getSemas

(

)

Get the one semaphore set.

The one semaphore set, if existing, will be registered and used as is.

Returns

0: OK found existing semaphore set; -1: error (errno set and errorText generated)

initialiseSemas()

int initialiseSemas

(

)

Initialise the one semaphore set.

The number of semaphores in the set is ANZ_SEMAS (default three). The one semaphore set, if existing, will be registered and used as is. If this is not possible it will be made and initialised.

Hint: This function has two OK return values!

Returns

1: OK semaphore set made new; 0: OK found existing semaphore set; -1: error (errno set and errorText generated)

semaphoreOperation()

int semaphoreOperation	(	int const	semNum,
		int const	op,
		int	ms
	)

Operation on one semaphore of the set.

Parameters

semNum	the semaphore number in the set (0..ANZ_SEMAS -1)
op	the semaphore operation
ms	if 2..20000 a timeout in ms

Returns

0: OK; -1: error (errno set and errorText generated)

semaphoreLock()

int semaphoreLock	(	int const	semNum,
		int	ms
	)

Lock one semaphore of the set.

Parameters

semNum	the semaphore number in the set (0..ANZ_SEMAS -1)
ms	if 2..20000 a timeout in ms

Returns

0: OK; -1: error (errno set and errorText generated)

semaphoreUnlock()

int semaphoreUnlock

(

int const

semNum

)

Unlock one semaphore of the set.

Parameters

semNum

the semaphore number in the set (0..ANZ_SEMAS -1)

Returns

0: OK; -1: error (errno set and errorText generated)

semaphoreClt()

int semaphoreClt	(	int const	semNum,
		int const	op,
		semCtlPar_t	par
	)

Control semaphores of the set.

Parameters

semNum	the semaphore number in the set (0..ANZ_SEMAS -1)
op	the semaphore operation, like e.g. SETVAL
par	op's parameter if any

Returns

0: OK; -1: error (errno set and errorText generated)

deleteSemas()

int deleteSemas

(

)

Delete the one semaphore set.

Server operation only.

Returns

0: OK; -1: error (errno set and errorText generated)

initialiseSharedMem()

void * initialiseSharedMem

(

)

Initialise shared memory.

Make or get and attach. return pointer to attached shared memory or (void *)-1

deleteSharedMem()

int deleteSharedMem

(

)

Delete and detach the shared memory.

Server operation only.

Variable Documentation

shMemSem

int shMemSem

extern

Semaphore set identifier.

The value returned by e.g. semget() (within getSemas() etc.) On success, semget() returns the semaphore set identifier (a nonnegative integer). On failure, -1 is returned, and errno is set to indicate the error.

shMemErrno

int shMemErrno

extern

Last error number of (some ) semaphore operations.