AscendingPageAllocator
is a fast and safe allocator that rounds all allocations to multiples of the system's page size. It reserves a range of virtual addresses (using mmap
on Posix and VirtualAlloc
on Windows) and allocates memory at consecutive virtual addresses.
When a chunk of memory is requested, the allocator finds a range of virtual pages that satisfy the requested size, changing their protection to read/write using OS primitives (mprotect
and VirtualProtect
, respectively). The physical memory is allocated on demand, when the pages are accessed.
Deallocation removes any read/write permissions from the target pages and notifies the OS to reclaim the physical memory, while keeping the virtual memory.
Because the allocator does not reuse memory, any dangling references to deallocated memory will always result in deterministically crashing the process.
size_t pageSize = 4096; size_t numPages = 100; void[] buf; void[] prevBuf = null; AscendingPageAllocator a = AscendingPageAllocator(numPages * pageSize); foreach (i; 0 .. numPages) { // Allocation is rounded up to page size buf = a.allocate(pageSize - 100); writeln(buf.length); // pageSize - 100 // Allocations are served at increasing addresses if (prevBuf) writeln(prevBuf.ptr + pageSize); // buf.ptr assert(a.deallocate(buf)); prevBuf = buf; }
Rounds the mapping size to the next multiple of the page size and calls the OS primitive responsible for creating memory mappings: mmap
on POSIX and VirtualAlloc
on Windows.
size_t n
| mapping size in bytes |
Rounds the requested size to the next multiple of the page size.
Decommit all physical memory associated with the buffer given as parameter, but keep the range of virtual addresses.
On POSIX systems deallocate
calls mmap
with `MAP_FIXED' a second time to decommit the memory. On Windows, it uses VirtualFree
with MEM_DECOMMIT
.
Returns Ternary.yes
if the passed buffer is inside the range of virtual adresses. Does not guarantee that the passed buffer is still valid.
Removes the memory mapping causing all physical memory to be decommited and the virtual address space to be reclaimed.
Returns the available size for further allocations in bytes.
Rounds the allocation size to the next multiple of the page size. The allocation only reserves a range of virtual pages but the actual physical memory is allocated on demand, when accessing the memory.
size_t n
| Bytes to allocate |
null
on failure or if the requested size exceeds the remaining capacity.Rounds the allocation size to the next multiple of the page size. The allocation only reserves a range of virtual pages but the actual physical memory is allocated on demand, when accessing the memory.
The allocated memory is aligned to the specified alignment a
.
size_t n
| Bytes to allocate |
uint a
| Alignment |
null
on failure or if the requested size exceeds the remaining capacity.If the passed buffer is not the last allocation, then delta
can be at most the number of bytes left on the last page. Otherwise, we can expand the last allocation until the end of the virtual address range.
Returns Ternary.yes
if the allocator does not contain any alive objects and Ternary.no
otherwise.
SharedAscendingPageAllocator
is the threadsafe version of AscendingPageAllocator
.
import core.thread : ThreadGroup; enum numThreads = 100; enum pageSize = 4096; shared SharedAscendingPageAllocator a = SharedAscendingPageAllocator(pageSize * numThreads); void fun() { void[] b = a.allocate(pageSize); writeln(b.length); // pageSize assert(a.deallocate(b)); } auto tg = new ThreadGroup; foreach (i; 0 .. numThreads) { tg.create(&fun); } tg.joinAll();
Rounds the mapping size to the next multiple of the page size and calls the OS primitive responsible for creating memory mappings: mmap
on POSIX and VirtualAlloc
on Windows.
size_t n
| mapping size in bytes |
Rounds the requested size to the next multiple of the page size.
Decommit all physical memory associated with the buffer given as parameter, but keep the range of virtual addresses.
On POSIX systems deallocate
calls mmap
with `MAP_FIXED' a second time to decommit the memory. On Windows, it uses VirtualFree
with MEM_DECOMMIT
.
Returns Ternary.yes
if the passed buffer is inside the range of virtual adresses. Does not guarantee that the passed buffer is still valid.
Removes the memory mapping causing all physical memory to be decommited and the virtual address space to be reclaimed.
Returns the available size for further allocations in bytes.
Rounds the allocation size to the next multiple of the page size. The allocation only reserves a range of virtual pages but the actual physical memory is allocated on demand, when accessing the memory.
size_t n
| Bytes to allocate |
null
on failure or if the requested size exceeds the remaining capacity.Rounds the allocation size to the next multiple of the page size. The allocation only reserves a range of virtual pages but the actual physical memory is allocated on demand, when accessing the memory.
The allocated memory is aligned to the specified alignment a
.
size_t n
| Bytes to allocate |
uint a
| Alignment |
null
on failure or if the requested size exceeds the remaining capacity.If the passed buffer is not the last allocation, then delta
can be at most the number of bytes left on the last page. Otherwise, we can expand the last allocation until the end of the virtual address range.
© 1999–2019 The D Language Foundation
Licensed under the Boost License 1.0.
https://dlang.org/phobos/std_experimental_allocator_building_blocks_ascending_page_allocator.html