VirtualMemory
(ply-system.h)

The VirtualMemory class is a platform-independent wrapper for mapping virtual memory to physical memory.

In C++ applications, memory is represented as a 32-bit or 64-bit address space known as virtual memory, which is divided into fixed-sized pages. Most pages are initially unusable and will cause an access violation or segmentation fault if accessed. To make pages usable, they must be mapped to physical memory by the underlying operating system.

System Information

static VirtualMemory::Properties VirtualMemory::getProperties()

Returns information about the system's virtual memory page size and allocation alignment. VirtualMemory::Properties has the following data members:

uptr regionAlignment	reserveRegion and allocRegion sizes must be a multiple of this.
uptr pageSize	commitPages sizes must be a multiple of this.

static VirtualMemory::SystemStats VirtualMemory::getSystemStats()

Returns platform-specific statistics about the current process's virtual memory usage. VirtualMemory::SystemStats has the following data members on Windows:

uptr privateUsage	Private memory allocated by the process.
uptr workingSetSize	Physical memory in the process working set.

On other platforms:

uptr virtualSize	Virtual address space used by the process.
uptr residentSize	Physical memory resident for the process.

Managing Pages

static void* VirtualMemory::reserveRegion(uptr numBytes)

Reserves a region of address space. Memory pages are initially uncommitted. Returns nullptr on failure. numBytes must be a multiple of regionAlignment.

static void VirtualMemory::unreserveRegion(void* addr, uptr numReservedBytes, uptr numCommittedBytes)

Unreserves a region of address space. numReservedBytes must match the argument passed to reserveRegion. Caller is responsible for passing the correct numCommittedBytes, otherwise stats will get out of sync.

static void VirtualMemory::commitPages(void* addr, uptr numBytes)

Commits a subregion of reserved address space, making it legal to read and write to the subregion. addr must be aligned to pageSize and numBytes must be a multiple of pageSize.

static void VirtualMemory::decommitPages(void* addr, uptr numBytes)

Decommits a subregion of previously committed memory. addr must be aligned to pageSize and numBytes must be a multiple of pageSize.

Allocating Large Blocks

static void* VirtualMemory::allocRegion(uptr numBytes)

Reserves and commits a region of address space. Returns nullptr on failure. Free using freeRegion. Don't decommit any pages in the returned region, otherwise stats will get out of sync. numBytes must be a multiple of regionAlignment.

static void VirtualMemory::freeRegion(void* addr, uptr numBytes)

Decommits and unreserves a region of address space. numBytes must match the argument passed to allocRegion.

Usage Stats