juce::MemoryMappedFile Class Reference

Maps a file into virtual memory for easy reading and/or writing. More...

#include <juce_MemoryMappedFile.h>

Collaboration diagram for juce::MemoryMappedFile:

Public Types
enum	AccessMode {   readOnly,   readWrite }
	The read/write flags used when opening a memory mapped file. More...

Public Member Functions
	MemoryMappedFile (const File &file, AccessMode mode, bool exclusive=false)
	Opens a file and maps it to an area of virtual memory. More...
	MemoryMappedFile (const File &file, const Range< int64 > &fileRange, AccessMode mode, bool exclusive=false)
	Opens a section of a file and maps it to an area of virtual memory. More...
	~MemoryMappedFile ()
	Destructor. More...
void *	getData () const noexcept
	Returns the address at which this file has been mapped, or a null pointer if the file couldn't be successfully mapped. More...
Range< int64 >	getRange () const noexcept
	Returns the section of the file at which the mapped memory represents. More...
size_t	getSize () const noexcept
	Returns the number of bytes of data that are available for reading or writing. More...

Private Member Functions
void	openInternal (const File &, AccessMode, bool)

Private Attributes
void *	address = nullptr
void *	fileHandle = nullptr
Range< int64 >	range

Detailed Description

Maps a file into virtual memory for easy reading and/or writing.

@tags{Core}

Member Enumeration Documentation

AccessMode

enum juce::MemoryMappedFile::AccessMode

The read/write flags used when opening a memory mapped file.

Enumerator
readOnly	Indicates that the memory can only be read.
readWrite	Indicates that the memory can be read and written to - changes that are made will be flushed back to disk at the whim of the OS.

Constructor & Destructor Documentation

MemoryMappedFile() [1/2]

juce::MemoryMappedFile::MemoryMappedFile	(	const File &	file,
		AccessMode	mode,
		bool	exclusive = false
	)

Opens a file and maps it to an area of virtual memory.

The file should already exist, and should already be the size that you want to work with when you call this. If the file is resized after being opened, the behaviour is undefined.

If the file exists and the operation succeeds, the getData() and getSize() methods will return the location and size of the data that can be read or written. Note that the entire file is not read into memory immediately - the OS simply creates a virtual mapping, which will lazily pull the data into memory when blocks are accessed.

If the file can't be opened for some reason, the getData() method will return a null pointer.

If exclusive is false then other apps can also open the same memory mapped file and use this mapping as an effective way of communicating. If exclusive is true then the mapped file will be opened exclusively - preventing other apps to access the file which may improve the performance of accessing the file.

MemoryMappedFile() [2/2]

juce::MemoryMappedFile::MemoryMappedFile	(	const File &	file,
		const Range< int64 > &	fileRange,
		AccessMode	mode,
		bool	exclusive = false
	)

Opens a section of a file and maps it to an area of virtual memory.

The file should already exist, and should already be the size that you want to work with when you call this. If the file is resized after being opened, the behaviour is undefined.

If the file exists and the operation succeeds, the getData() and getSize() methods will return the location and size of the data that can be read or written. Note that the entire file is not read into memory immediately - the OS simply creates a virtual mapping, which will lazily pull the data into memory when blocks are accessed.

If the file can't be opened for some reason, the getData() method will return a null pointer.

NOTE: The start of the actual range used may be rounded-down to a multiple of the OS's page-size, so do not assume that the mapped memory will begin at exactly the position you requested - always use getRange() to check the actual range that is being used.

~MemoryMappedFile()

juce::MemoryMappedFile::~MemoryMappedFile

(

)

Destructor.

References address, fileHandle, juce::Range< ValueType >::getLength(), and range.

Member Function Documentation

getData()

void* juce::MemoryMappedFile::getData ( ) const

inlinenoexcept

Returns the address at which this file has been mapped, or a null pointer if the file couldn't be successfully mapped.

References juce::gl::address.

getRange()

Range<int64> juce::MemoryMappedFile::getRange ( ) const

inlinenoexcept

Returns the section of the file at which the mapped memory represents.

References juce::gl::range.

getSize()

size_t juce::MemoryMappedFile::getSize ( ) const

inlinenoexcept

Returns the number of bytes of data that are available for reading or writing.

This will normally be the size of the file.

References juce::gl::range.

openInternal()

void juce::MemoryMappedFile::openInternal ( const File &  file, AccessMode  mode, bool  exclusive  )

private

References address, juce::exclusive, fileHandle, juce::File::getFullPathName(), juce::Range< ValueType >::getLength(), juce::Range< ValueType >::getStart(), jassert, juce::gl::m, juce::gl::mode, range, readOnly, readWrite, juce::Range< ValueType >::setStart(), and juce::String::toUTF8().

Member Data Documentation

address

void* juce::MemoryMappedFile::address = nullptr

private

Referenced by openInternal(), and ~MemoryMappedFile().

fileHandle

void* juce::MemoryMappedFile::fileHandle = nullptr

private

Referenced by openInternal(), and ~MemoryMappedFile().

range

Range<int64> juce::MemoryMappedFile::range

private

Referenced by openInternal(), and ~MemoryMappedFile().

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

• juce_MemoryMappedFile.h
• juce_posix_SharedCode.h