vlink::SysSharemem Class Reference

Named cross-process shared-memory region with read-only or read-write mappings. More...

#include <sys_sharemem.h>

Collaboration diagram for vlink::SysSharemem:

Public Types
enum	Mode : uint8_t { kReadOnly = 0 , kReadWrite = 1 }
	Access mode applied to the mapping. More...

Public Member Functions
	SysSharemem ()
	Constructs a wrapper in the detached state. More...
	~SysSharemem ()
	Destructor. Invokes detach(false) when the wrapper is still attached. More...
bool	create (const std::string &name, size_t size, Mode mode=kReadWrite)
	Creates and maps a new shared-memory region of size bytes under name. More...
bool	attach (const std::string &name, Mode mode=kReadWrite)
	Attaches to an existing shared-memory region previously created with the same name. More...
bool	detach (bool force=true)
	Unmaps the region and optionally unlinks the kernel name. More...
bool	is_attached () const
	Reports whether the wrapper currently owns a mapping. More...
void *	data ()
	Returns a writable pointer to the start of the mapping. More...
const void *	data () const
	Returns a read-only pointer to the start of the mapping. More...
size_t	size () const
	Returns the size of the mapping in bytes. More...

Detailed Description

Named cross-process shared-memory region with read-only or read-write mappings.

Manages one mapping at a time; call detach() before re-attaching to a different region.

Member Enumeration Documentation

Mode

enum vlink::SysSharemem::Mode : uint8_t

Access mode applied to the mapping.

Enumerator names mirror the POSIX O_RDONLY / O_RDWR open flags. On Windows the implementation translates these to the equivalent CreateFileMapping / MapViewOfFile page-protection constants; the observable behaviour is identical across platforms.

Enumerator
kReadOnly	Read-only mapping; writes through data() are undefined.
kReadWrite	Read-write mapping (default).

Constructor & Destructor Documentation

SysSharemem()

vlink::SysSharemem::SysSharemem

(

)

Constructs a wrapper in the detached state.

~SysSharemem()

vlink::SysSharemem::~SysSharemem

(

)

Destructor. Invokes detach(false) when the wrapper is still attached.

Member Function Documentation

attach()

bool vlink::SysSharemem::attach	(	const std::string &	name,
		Mode	mode = kReadWrite
	)

Attaches to an existing shared-memory region previously created with the same name.

Parameters

name	Kernel-name of the region.
mode	Access mode for the mapping. Default: kReadWrite.

Returns

true on success.

create()

bool vlink::SysSharemem::create	(	const std::string &	name,
		size_t	size,
		Mode	mode = kReadWrite
	)

Creates and maps a new shared-memory region of size bytes under name.

Fails when a region with name already exists in the kernel namespace. The supported POSIX/Windows backends provide zero-initialised storage.

Parameters

name	Kernel-name for the region. POSIX must begin with '/'.
size	Region size in bytes.
mode	Access mode for the mapping. Default: kReadWrite.

Returns

true on success.

data() [1/2]

void* vlink::SysSharemem::data

(

)

Returns a writable pointer to the start of the mapping.

Returns

Mapping base pointer; nullptr when detached or in read-only mode.

data() [2/2]

const void* vlink::SysSharemem::data

(

)

const

Returns a read-only pointer to the start of the mapping.

Returns

Const mapping base pointer; nullptr when detached.

detach()

bool vlink::SysSharemem::detach

(

bool

force = true

)

Unmaps the region and optionally unlinks the kernel name.

Parameters

force

When true, POSIX backends call shm_unlink so the region is removed from the kernel namespace. Other processes that still hold mappings keep them. Windows merely closes the local mapping handle. Default: true.

Returns

true on success.

is_attached()

bool vlink::SysSharemem::is_attached

(

)

const

Reports whether the wrapper currently owns a mapping.

Returns

true after a successful create or attach.

size()

size_t vlink::SysSharemem::size

(

)

const

Returns the size of the mapping in bytes.

Returns

Region size; 0 when detached.

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

• include/vlink/base/sys_sharemem.h