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API reference / Windows

VirtualMemory class

Owns one region allocated with VirtualAlloc.

Use
import ThinkMeta.ConcurrentTasks.Windows.VirtualMemory;
Namespace
ThinkMeta::ConcurrentTasks::Windows

Syntax

class VirtualMemory

Remarks

The region is released (MEM_RELEASE) on destruction. Only the owner calls Reserve and Release, from one thread at a time; the static members act on any address and are as thread-safe as the Win32 calls they wrap.

See also

Memory::SpscVirtualMemoryPipe

Constructors

VirtualMemory

Constructs an object that owns no memory.

Syntax

VirtualMemory() noexcept = default;

Allocates a region (VirtualAlloc).

Syntax

VirtualMemory(std::size_t size, DWORD allocationType, DWORD protection) noexcept;

Parameters

sizestd::size_t
Size in bytes; rounded up to whole pages.
allocationTypeDWORD
MEM_RESERVE, MEM_COMMIT or both, optionally with MEM_LARGE_PAGES or MEM_TOP_DOWN.
protectionDWORD
Page protection, e.g. PAGE_READWRITE or PAGE_NOACCESS.

Remarks

Calls VirtualAlloc(nullptr, size, allocationType, protection). Check IsValid; on failure GetLastError has the reason.

~VirtualMemory

Releases the region, if any.

Syntax

~VirtualMemory() noexcept;

Methods

IsValid

Returns whether the object owns a region.

Syntax

bool IsValid() const noexcept;

Return value

Type: bool

true if a region is owned; otherwise false.

GetAllocationBase

Returns the start of the region, or nullptr.

Syntax

void* GetAllocationBase() noexcept;

Return value

Type: void*

The region's base address; nullptr if the object owns no region.

AtOffset

Returns the address offset bytes into the region.

Syntax

void* AtOffset(std::size_t offset) noexcept;

Parameters

offsetstd::size_t
Distance in bytes from the start of the region; must lie inside it.

Return value

Type: void*

The region's base address plus offset.

Remarks

No bounds check.

Reserve

Reserves address space.

Syntax

ErrorCode Reserve(std::size_t size) noexcept;

Parameters

sizestd::size_t
Bytes to reserve (MEM_RESERVE, PAGE_NOACCESS).

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Remarks

Releases the current region, if any, first. Pages must be committed (Commit) before they are touched.

See also

Release

Release

Releases the whole region (MEM_RELEASE).

Syntax

ErrorCode Release() noexcept;

Return value

Type: ErrorCode

Error::Success (0) on success, also if there was nothing to release; otherwise the Win32 error code.

Remarks

The object owns nothing afterwards, even if VirtualFree failed.

See also

Reserve

Commit

Commits pages (MEM_COMMIT).

Syntax

static ErrorCode Commit(void* address, std::size_t size, DWORD protection) noexcept;

Parameters

addressvoid*
Start of the range; rounded down to a page boundary.
sizestd::size_t
Length of the range in bytes; every page it touches is committed.
protectionDWORD
Page protection, e.g. PAGE_READWRITE.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Remarks

The range must lie inside an existing reservation.

See also

Decommit

Decommit

Decommits pages (MEM_DECOMMIT).

Syntax

static ErrorCode Decommit(void* address, std::size_t size) noexcept;

Parameters

addressvoid*
Start of the range; rounded down to a page boundary.
sizestd::size_t
Length of the range in bytes; every page it touches is decommitted.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Remarks

The address range stays reserved.

See also

Commit

Lock

Locks pages into physical memory (VirtualLock).

Syntax

static ErrorCode Lock(void* address, std::size_t size) noexcept;

Parameters

addressvoid*
Start of the range; the pages must be committed.
sizestd::size_t
Length of the range in bytes; every page it touches is locked.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Remarks

Limited by the working set size.

See also

Unlock

Unlock

Unlocks pages locked with Lock (VirtualUnlock).

Syntax

static ErrorCode Unlock(void* address, std::size_t size) noexcept;

Parameters

addressvoid*
Start of the range.
sizestd::size_t
Length of the range in bytes; every page it touches is unlocked.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Protect

Changes the protection of committed pages (VirtualProtect).

Syntax

static ErrorCode Protect(
    void* address,
    std::size_t size,
    DWORD protection,
    DWORD* oldProtection
) noexcept;

Parameters

addressvoid*
Start of the range; the pages must be committed.
sizestd::size_t
Length of the range in bytes; every page it touches changes.
protectionDWORD
The new page protection, e.g. PAGE_READONLY.
oldProtectionDWORD*
Receives the old protection of the first page; required.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Changes the protection of committed pages (VirtualProtect).

Syntax

static ErrorCode Protect(
    void* address,
    std::size_t size,
    DWORD protection
) noexcept;

Parameters

addressvoid*
Start of the range; the pages must be committed.
sizestd::size_t
Length of the range in bytes; every page it touches changes.
protectionDWORD
The new page protection, e.g. PAGE_READONLY.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

Remarks

Discards the old protection.

Query

Describes the pages around an address (VirtualQuery).

Syntax

static ErrorCode Query(const void* address, MEMORY_BASIC_INFORMATION* mbi) noexcept;

Parameters

addressconst void*
Any address; the pages around it are described.
mbiMEMORY_BASIC_INFORMATION*
Receives the description; required.

Return value

Type: ErrorCode

Error::Success (0) on success; otherwise the Win32 error code.

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