asmjit::JitAllocator Class Reference

A simple implementation of memory manager that uses asmjit::VirtMem functions to manage virtual memory for JIT compiled code.

Implementation notes:

• Granularity of allocated blocks is different than granularity for a typical C malloc. In addition, the allocator can use several memory pools having a different granularity to minimize the maintenance overhead. Multiple pools feature requires kFlagUseMultiplePools flag to be set.
• The allocator doesn't store any information in executable memory, instead, the implementation uses two bit-vectors to manage allocated memory of each allocator-block. The first bit-vector called 'used' is used to track used memory (where each bit represents memory size defined by granularity) and the second bit vector called 'stop' is used as a sentinel to mark where the allocated area ends.
• Internally, the allocator also uses RB tree to keep track of all blocks across all pools. Each inserted block is added to the tree so it can be matched fast during release() and shrink().

Public Members

Members

Impl* _impl

Classes

struct CreateParams

struct Impl

class Span

struct Statistics

class WriteScope

Member Functions

JitAllocator(const JitAllocator& other) = delete

JitAllocator& operator=(const JitAllocator& other) = delete

Construction & Destruction

JitAllocator(const CreateParams* params = nullptr) noexcept

~JitAllocator() noexcept

bool isInitialized() const noexcept

void reset(ResetPolicy resetPolicy = ResetPolicy::kSoft) noexcept

Accessors

JitAllocatorOptions options() const noexcept

bool hasOption(JitAllocatorOptions option) const noexcept

uint32_t blockSize() const noexcept

uint32_t granularity() const noexcept

uint32_t fillPattern() const noexcept

Alloc & Release

Error alloc(Span& out, size_t size) noexcept

Error release(void* rx) noexcept

Error shrink(Span& span, size_t newSize) noexcept

Error query(Span& out, void* rx) const noexcept

Statistics

Statistics statistics() const noexcept

Write Operations

typedef Error(* WriteFunc)(Span& span, void* userData) noexcept

Error write(Span& span, size_t offset, const void* src, size_t size, VirtMem::CachePolicy policy = VirtMem::CachePolicy::kDefault) noexcept

Error write(Span& span, WriteFunc writeFunc, void* userData, VirtMem::CachePolicy policy = VirtMem::CachePolicy::kDefault) noexcept

template<class Lambda>

Error write(Span& span, Lambda&& lambdaFunc, VirtMem::CachePolicy policy = VirtMem::CachePolicy::kDefault) noexcept

Constructor & Destructor Documentation

JitAllocator::JitAllocator(const CreateParams* params = nullptr)explicitnoexcept

Creates a JitAllocator instance.

JitAllocator::~JitAllocator()noexcept

Destroys the JitAllocator instance and release all blocks held.

Member Function Documentation

void JitAllocator::reset(ResetPolicy resetPolicy = ResetPolicy::kSoft)noexcept

Free all allocated memory - makes all pointers returned by alloc() invalid.

Remarks

This function is not thread-safe as it's designed to be used when nobody else is using allocator. The reason is that there is no point of calling reset() when the allocator is still in use.

JitAllocatorOptions JitAllocator::options() constnoexcept

Returns allocator options, see Flags.

bool JitAllocator::hasOption(JitAllocatorOptions option) constnoexcept

Tests whether the allocator has the given option set.

uint32_t JitAllocator::blockSize() constnoexcept

Returns a base block size (a minimum size of block that the allocator would allocate).

uint32_t JitAllocator::granularity() constnoexcept

Returns granularity of the allocator.

uint32_t JitAllocator::fillPattern() constnoexcept

Returns pattern that is used to fill unused memory if kFlagUseFillPattern is set.

Error JitAllocator::alloc(Span& out, size_t size)noexcept

Allocates a new memory span of the requested size.

Error JitAllocator::release(void* rx)noexcept

Releases a memory block returned by alloc().

Remarks

This function is thread-safe.

Error JitAllocator::shrink(Span& span, size_t newSize)noexcept

Frees extra memory allocated with rx by shrinking it to the given newSize.

Remarks

This function is thread-safe.

Error JitAllocator::query(Span& out, void* rx) constnoexcept

Queries information about an allocated memory block that contains the given rx, and writes it to out.

If the pointer is matched, the function returns kErrorOk and fills out with the corresponding span.

Statistics JitAllocator::statistics() constnoexcept

Returns JIT allocator statistics.

Remarks

This function is thread-safe.

Member Data Documentation

Impl* JitAllocator::_impl

Allocator implementation (private).