icl::io::SharedMemorySegment Class Reference

Implementation of a cross-process shared memory. More...

#include <SharedMemorySegment.h>

Public Member Functions
	SharedMemorySegment (std::string name="", int minsize=1)
	Creates a SharedMemorySegment instance. More...
	~SharedMemorySegment ()
	The destructor basically calls release. More...
void	release ()
	Releases the acuired SharedMemorySegment. More...
std::string	getName ()
	Returns the current SharedMemorySegments name. More...
void	reset (std::string name, int minsize=0)
	Sets name and minsize to the passed values. More...
bool	isAttached ()
	Tells whether this instance is currently attached to a SharedMemory. More...
bool	lock (int minsize=0)
	Locks the underlying SharedMemorySegment, aquireing when needed. More...
bool	unlock ()
	Unlocks the underlying SharedMemorySegment. More...
void	forceMinSize (int minsize)
	Forces a resize of the SharedMemory to the passed minsize. More...
int	getSize ()
	Returns the current size of the SharedMemorySegment in bytes. More...
bool	isEmpty () const
	Tells whether the Segment is empty. More...
void *	data ()
	getter for the MemorySegment data. More...
const void *	data () const
	implicit const getter for the MemorySegment data. More...
const void *	constData () const
	explicit const getter for the MemorySegment data. More...

Private Attributes
utils::Mutex	m_Mutex
	instance locking More...
Impl *	m_Impl
	pointer to the internal implementation More...
std::string	m_Name
	the current name of the SharedMemorySegment More...
int	m_Minsize
	local minimal size tf the Segment More...

Detailed Description

Implementation of a cross-process shared memory.

The SharedMemorySegment can be used to share information between multiple processes on a single system.

This class uses in iternal singleton implementation and map allowing multiple thereads to read a ShredMemory concurrent. The drawback is that external locking is needed for concurrent reading and writing.

Created SharedMemorySegments are registered via the SharedMemorySegmentRegister.

A signal handler is installed to ensure that all SharedMemorySegments are released.

Constructor & Destructor Documentation

SharedMemorySegment()

icl::io::SharedMemorySegment::SharedMemorySegment	(	std::string	name = "",
		int	minsize = 1
	)

Creates a SharedMemorySegment instance.

No memory allocation is done here. To connect to the corresponding SharedMemorySegment call lock().

Parameters

name	The name identifying the segment.
minsize	The minimal needed size.

~SharedMemorySegment()

icl::io::SharedMemorySegment::~SharedMemorySegment

(

)

The destructor basically calls release.

Member Function Documentation

constData()

const void* icl::io::SharedMemorySegment::constData

(

)

const

explicit const getter for the MemorySegment data.

Returns

a pointer to the memory block. Null when not attached or not locked.

data() [1/2]

void* icl::io::SharedMemorySegment::data

(

)

getter for the MemorySegment data.

Returns

a pointer to the memory block. Null when not attached or not locked.

data() [2/2]

const void* icl::io::SharedMemorySegment::data

(

)

const

implicit const getter for the MemorySegment data.

Returns

a pointer to the memory block. Null when not attached or not locked.

forceMinSize()

void icl::io::SharedMemorySegment::forceMinSize

(

int

minsize

)

Forces a resize of the SharedMemory to the passed minsize.

This can shrink the SharedMemorySegment when the current space is no longer needed. It will force a recreation of the underlying SharedMemory to the passed size. It will not prevend other processes from re-enlarging the Segment. Caution: Don't use this to ensure that the SharedMemory is large enough. Call lock() with the desired size instead.

getName()

std::string icl::io::SharedMemorySegment::getName

(

)

Returns the current SharedMemorySegments name.

getSize()

int icl::io::SharedMemorySegment::getSize

(

)

Returns the current size of the SharedMemorySegment in bytes.

Returns

-1 when this instance is not attached

isAttached()

bool icl::io::SharedMemorySegment::isAttached

(

)

Tells whether this instance is currently attached to a SharedMemory.

Attachment is performed lock() and detachment release().

isEmpty()

bool icl::io::SharedMemorySegment::isEmpty

(

)

const

Tells whether the Segment is empty.

Basically checks whether all data bits are zero. A freshly created SharedMemorySegment is always overwritten with zeros.

lock()

bool icl::io::SharedMemorySegment::lock

(

int

minsize = 0

)

Locks the underlying SharedMemorySegment, aquireing when needed.

Here happens all the fun. When this instance is not connected, it will be connected. When minsize > getSize or a resize is requested, this will detach and reattach/recreate with the needed size. Every call to lock needs a call to unlock. Multiple threads of the same process cat get the lock simultaneously. That way, concurrent access in one process is possible but extra locking is necessary when this is not desired. Can return true without having the necessary size when already locked by this process.

Returns

whether the segment is locked. may sometimes not be reached, when this process already holds the lock.

release()

void icl::io::SharedMemorySegment::release

(

)

Releases the acuired SharedMemorySegment.

When the last instance calls release the underlying singleton implementation unlocks and detatches from the systems SharedMemory.

reset()

void icl::io::SharedMemorySegment::reset	(	std::string	name,
		int	minsize = 0
	)

Sets name and minsize to the passed values.

This function just sets the variables. Potential releasing and reattaching happens on the following lock().

unlock()

bool icl::io::SharedMemorySegment::unlock

(

)

Unlocks the underlying SharedMemorySegment.

Returns

whether the segment is not locked. true when still locked.

Member Data Documentation

m_Impl

Impl* icl::io::SharedMemorySegment::m_Impl

private

pointer to the internal implementation

m_Minsize

int icl::io::SharedMemorySegment::m_Minsize

private

local minimal size tf the Segment

m_Mutex

utils::Mutex icl::io::SharedMemorySegment::m_Mutex

mutableprivate

instance locking

m_Name

std::string icl::io::SharedMemorySegment::m_Name

private

the current name of the SharedMemorySegment

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The documentation for this class was generated from the following file:

• /Users/alneuman/vm/icl/ICLIO/src/ICLIO/SharedMemorySegment.h