PageAllocator Class Reference

#include <v8-platform.h>

Data Structures
class	SharedMemory
class	SharedMemoryMapping

Public Types
enum	Permission {   kNoAccess , kRead , kReadWrite , kReadWriteExecute ,   kReadExecute , kNoAccessWillJitLater }

Public Member Functions
virtual	~PageAllocator ()=default
virtual size_t	AllocatePageSize ()=0
virtual size_t	CommitPageSize ()=0
virtual void	SetRandomMmapSeed (int64_t seed)=0
virtual void *	GetRandomMmapAddr ()=0
virtual void *	AllocatePages (void *address, size_t length, size_t alignment, Permission permissions)=0
virtual bool	FreePages (void *address, size_t length)=0
virtual bool	ReleasePages (void *address, size_t length, size_t new_length)=0
virtual bool	SetPermissions (void *address, size_t length, Permission permissions)=0
virtual bool	RecommitPages (void *address, size_t length, Permission permissions)
virtual bool	DiscardSystemPages (void *address, size_t size)
virtual bool	DecommitPages (void *address, size_t size)=0
virtual bool	ReserveForSharedMemoryMapping (void *address, size_t size)
virtual std::unique_ptr< SharedMemory >	AllocateSharedPages (size_t length, const void *original_address)
virtual bool	CanAllocateSharedPages ()

Detailed Description

A V8 memory page allocator.

Can be implemented by an embedder to manage large host OS allocations.

Definition at line 450 of file v8-platform.h.

Member Enumeration Documentation

Permission

enum Permission

Memory permissions.

Enumerator
kNoAccess
kRead
kReadWrite
kReadWriteExecute
kReadExecute
kNoAccessWillJitLater

Definition at line 481 of file v8-platform.h.

Constructor & Destructor Documentation

~PageAllocator()

virtual ~PageAllocator ( )

virtualdefault

Member Function Documentation

AllocatePages()

virtual void * AllocatePages ( void *  address, size_t  length, size_t  alignment, Permission  permissions  )

pure virtual

Allocates memory in range with the given alignment and permission.

AllocatePageSize()

virtual size_t AllocatePageSize ( )

pure virtual

Gets the page granularity for AllocatePages and FreePages. Addresses and lengths for those calls should be multiples of AllocatePageSize().

AllocateSharedPages()

virtual std::unique_ptr< SharedMemory > AllocateSharedPages ( size_t  length, const void *  original_address  )

inlinevirtual

INTERNAL ONLY: This interface has not been stabilised and may change without notice from one release to another without being deprecated first.

Allocates shared memory pages. Not all PageAllocators need support this and so this method need not be overridden. Allocates a new read-only shared memory region of size |length| and copies the memory at |original_address| into it.

Definition at line 598 of file v8-platform.h.

CanAllocateSharedPages()

virtual bool CanAllocateSharedPages ( )

inlinevirtual

INTERNAL ONLY: This interface has not been stabilised and may change without notice from one release to another without being deprecated first.

If not overridden and changed to return true, V8 will not attempt to call AllocateSharedPages or RemapSharedPages. If overridden, AllocateSharedPages and RemapSharedPages must also be overridden.

Definition at line 611 of file v8-platform.h.

CommitPageSize()

virtual size_t CommitPageSize ( )

pure virtual

Gets the page granularity for SetPermissions and ReleasePages. Addresses and lengths for those calls should be multiples of CommitPageSize().

DecommitPages()

virtual bool DecommitPages ( void *  address, size_t  size  )

pure virtual

Decommits any wired memory pages in the given range, allowing the OS to reclaim them, and marks the region as inacessible (kNoAccess). The address range stays reserved and can be accessed again later by changing its permissions. However, in that case the memory content is guaranteed to be zero-initialized again. The memory must have been previously allocated by a call to AllocatePages. Returns true on success, false otherwise.

DiscardSystemPages()

virtual bool DiscardSystemPages ( void *  address, size_t  size  )

inlinevirtual

Frees memory in the given [address, address + size) range. address and size should be operating system page-aligned. The next write to this memory area brings the memory transparently back. This should be treated as a hint to the OS that the pages are no longer needed. It does not guarantee that the pages will be discarded immediately or at all.

Definition at line 538 of file v8-platform.h.

FreePages()

virtual bool FreePages ( void *  address, size_t  length  )

pure virtual

Frees memory in a range that was allocated by a call to AllocatePages.

GetRandomMmapAddr()

virtual void * GetRandomMmapAddr ( )

pure virtual

Returns a randomized address, suitable for memory allocation under ASLR. The address will be aligned to AllocatePageSize.

RecommitPages()

virtual bool RecommitPages ( void *  address, size_t  length, Permission  permissions  )

inlinevirtual

Recommits discarded pages in the given range with given permissions. Discarded pages must be recommitted with their original permissions before they are used again.

Definition at line 525 of file v8-platform.h.

ReleasePages()

virtual bool ReleasePages ( void *  address, size_t  length, size_t  new_length  )

pure virtual

Releases memory in a range that was allocated by a call to AllocatePages.

ReserveForSharedMemoryMapping()

virtual bool ReserveForSharedMemoryMapping ( void *  address, size_t  size  )

inlinevirtual

INTERNAL ONLY: This interface has not been stabilised and may change without notice from one release to another without being deprecated first.

Reserve pages at a fixed address returning whether the reservation is possible. The reserved memory is detached from the PageAllocator and so should not be freed by it. It's intended for use with SharedMemory::RemapTo, where ~SharedMemoryMapping would free the memory.

Definition at line 585 of file v8-platform.h.

SetPermissions()

virtual bool SetPermissions ( void *  address, size_t  length, Permission  permissions  )

pure virtual

Sets permissions on pages in an allocated range.

SetRandomMmapSeed()

virtual void SetRandomMmapSeed ( int64_t  seed )

pure virtual

Sets the random seed so that GetRandomMmapAddr() will generate repeatable sequences of random mmap addresses.

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

• include/v8-platform.h