ImageMagick (legacy) – MagickCore, C API: Memory Allocation
Author: ImageMagick Studio LLC
Description: Create, Edit, Compose, or Convert Digital Images
Keywords: magickcore, c, api:, memory, allocation, image processing software

## AcquireCriticalMemory

AcquireCriticalMemory(): allocate a small memory request with AcquireMagickMemory(), however, on fail throw a fatal exception and exit. Free the memory reserve with RelinquishMagickMemory(). AcquireAlignedMemory(): allocate a small memory request that is aligned on a cache line. On fail, return NULL for possible recovery. Free the memory reserve with RelinquishMagickMemory(). AcquireMagickMemory()/ResizeMagickMemory(): allocate a small to medium memory request, typically with malloc()/realloc(). On fail, return NULL for possible recovery. Free the memory reserve with RelinquishMagickMemory(). AcquireQuantumMemory()/ResizeQuantumMemory(): allocate a small to medium memory request. This is a secure memory allocator as it accepts two parameters, count and quantum, to ensure the request does not overflow. It also check to ensure the request does not exceed the maximum memory per the security policy. Free the memory reserve with RelinquishMagickMemory(). AcquireVirtualMemory(): allocate a large memory request either in heap, memory-mapped, or memory-mapped on disk depending on whether heap allocation fails or if the request exceeds the maximum memory policy. Free the memory reserve with RelinquishVirtualMemory(). ResetMagickMemory(): fills the bytes of the memory area with a constant byte.

In addition, we provide hooks for your own memory constructor/destructors.

utilize our internal custom allocator as follows

Segregate our memory requirements from any program that calls our API. This should help reduce the risk of others changing our program state or causing memory corruption.

Our custom memory allocation manager implements a best-fit allocation policy using segregated free lists. It uses a linear distribution of size classes for lower sizes and a power of two distribution of size classes at higher sizes. It is based on the paper, "Fast Memory Allocation using Lazy Fits." written by Yoo C. Chung.

By default, C's standard library is used (e.g. malloc); use the custom memory allocator by defining MAGICKCORE_ANONYMOUS_MEMORY_SUPPORT to allocate memory with private anonymous mapping rather than from the heap.

## AcquireAlignedMemory

AcquireAlignedMemory() returns a pointer to a block of memory whose size is at least (count*quantum) bytes, and whose address is aligned on a cache line.

The format of the AcquireAlignedMemory method is:

    void *AcquireAlignedMemory(const size_t count,const size_t quantum)

A description of each parameter follows:

count
  the number of objects to allocate contiguously.
quantum
  the size (in bytes) of each object.

## AcquireMagickMemory

AcquireMagickMemory() returns a pointer to a block of memory at least size bytes suitably aligned for any use.

The format of the AcquireMagickMemory method is:

    void *AcquireMagickMemory(const size_t size)

A description of each parameter follows:

size
  the size of the memory in bytes to allocate.

## AcquireCriticalMemory

AcquireCriticalMemory() is just like AcquireMagickMemory(), throws a fatal exception if the memory cannot be acquired.

That is, AcquireCriticalMemory() returns a pointer to a block of memory that is at least size bytes, and that is suitably aligned for any use; however, if this is not possible, it throws an exception and terminates the program as unceremoniously as possible.

The format of the AcquireCriticalMemory method is:

    void *AcquireCriticalMemory(const size_t size)

A description of each parameter follows:

size
  the size (in bytes) of the memory to allocate.

## AcquireQuantumMemory

AcquireQuantumMemory() returns a pointer to a block of memory at least count * quantum bytes suitably aligned for any use.

The format of the AcquireQuantumMemory method is:

    void *AcquireQuantumMemory(const size_t count,const size_t quantum)

A description of each parameter follows:

count
  the number of objects to allocate contiguously.
quantum
  the size (in bytes) of each object.

## AcquireVirtualMemory

AcquireVirtualMemory() allocates a pointer to a block of memory at least size bytes suitably aligned for any use. In addition to heap, it also supports memory-mapped and file-based memory-mapped memory requests.

The format of the AcquireVirtualMemory method is:

    MemoryInfo *AcquireVirtualMemory(const size_t count,const size_t quantum)

A description of each parameter follows:

count
  the number of objects to allocate contiguously.
quantum
  the size (in bytes) of each object.

## CopyMagickMemory

CopyMagickMemory() copies size bytes from memory area source to the destination. Copying between objects that overlap will take place correctly. It returns destination.

The format of the CopyMagickMemory method is:

    void *CopyMagickMemory(void *magick_restrict destination,
      const void *magick_restrict source,const size_t size)

A description of each parameter follows:

destination
  the destination.
source
  the source.
size
  the size of the memory in bytes to allocate.

## GetMagickMemoryMethods

GetMagickMemoryMethods() gets the methods to acquire, resize, and destroy memory.

The format of the GetMagickMemoryMethods() method is:

    void GetMagickMemoryMethods(AcquireMemoryHandler *acquire_memory_handler,
      ResizeMemoryHandler *resize_memory_handler,
      DestroyMemoryHandler *destroy_memory_handler)

A description of each parameter follows:

acquire_memory_handler
  method to acquire memory (e.g. malloc).
resize_memory_handler
  method to resize memory (e.g. realloc).
destroy_memory_handler
  method to destroy memory (e.g. free).

## GetVirtualMemoryBlob

GetVirtualMemoryBlob() returns the virtual memory blob associated with the specified MemoryInfo structure.

The format of the GetVirtualMemoryBlob method is:

    void *GetVirtualMemoryBlob(const MemoryInfo *memory_info)

A description of each parameter follows:

memory_info
  The MemoryInfo structure.

## RelinquishAlignedMemory

RelinquishAlignedMemory() frees memory acquired with AcquireAlignedMemory() or reuse.

The format of the RelinquishAlignedMemory method is:

    void *RelinquishAlignedMemory(void *memory)

A description of each parameter follows:

memory
  A pointer to a block of memory to free for reuse.

## RelinquishMagickMemory

RelinquishMagickMemory() frees memory acquired with AcquireMagickMemory() or AcquireQuantumMemory() for reuse.

The format of the RelinquishMagickMemory method is:

    void *RelinquishMagickMemory(void *memory)

A description of each parameter follows:

memory
  A pointer to a block of memory to free for reuse.

## RelinquishVirtualMemory

RelinquishVirtualMemory() frees memory acquired with AcquireVirtualMemory().

The format of the RelinquishVirtualMemory method is:

    MemoryInfo *RelinquishVirtualMemory(MemoryInfo *memory_info)

A description of each parameter follows:

memory_info
  A pointer to a block of memory to free for reuse.

## ResetMagickMemory

ResetMagickMemory() fills the first size bytes of the memory area pointed to by memory with the constant byte c. We use a volatile pointer when updating the byte string. Most compilers will avoid optimizing away access to a volatile pointer, even if the pointer appears to be unused after the call.

The format of the ResetMagickMemory method is:

    void *ResetMagickMemory(void *memory,int c,const size_t size)

A description of each parameter follows:

memory
  a pointer to a memory allocation.
c
  set the memory to this value.
size
  size of the memory to reset.

## ResizeMagickMemory

ResizeMagickMemory() changes the size of the memory and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes.

The format of the ResizeMagickMemory method is:

    void *ResizeMagickMemory(void *memory,const size_t size)

A description of each parameter follows:

memory
  A pointer to a memory allocation.
size
  the new size of the allocated memory.

## ResizeQuantumMemory

ResizeQuantumMemory() changes the size of the memory and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes.

The format of the ResizeQuantumMemory method is:

    void *ResizeQuantumMemory(void *memory,const size_t count,
      const size_t quantum)

A description of each parameter follows:

memory
  A pointer to a memory allocation.
count
  the number of objects to allocate contiguously.
quantum
  the size (in bytes) of each object.

## SetMagickAlignedMemoryMethods

SetMagickAlignedMemoryMethods() sets the methods to acquire and relinquish aligned memory.

The format of the SetMagickAlignedMemoryMethods() method is:

    SetMagickAlignedMemoryMethods(
      AcquireAlignedMemoryHandler acquire_aligned_memory_handler,
      RelinquishAlignedMemoryHandler relinquish_aligned_memory_handler)

A description of each parameter follows:

acquire_memory_handler
  method to acquire aligned memory.
relinquish_aligned_memory_handler
  method to relinquish aligned memory.

## SetMagickMemoryMethods

SetMagickMemoryMethods() sets the methods to acquire, resize, and destroy memory. Your custom memory methods must be set prior to the MagickCoreGenesis() method.

The format of the SetMagickMemoryMethods() method is:

    SetMagickMemoryMethods(AcquireMemoryHandler acquire_memory_handler,
      ResizeMemoryHandler resize_memory_handler,
      DestroyMemoryHandler destroy_memory_handler)

A description of each parameter follows:

acquire_memory_handler
  method to acquire memory (e.g. malloc).
resize_memory_handler
  method to resize memory (e.g. realloc).
destroy_memory_handler
  method to destroy memory (e.g. free).

## ShredMagickMemory

ShredMagickMemory() overwrites the specified memory buffer with random data. The overwrite is optional and is only required to help keep the contents of the memory buffer private.

The format of the ShredMagickMemory method is:

    MagickBooleanType ShredMagickMemory(void *memory,const size_t length)

A description of each parameter follows.

memory

Specifies the memory buffer.

length

Specifies the length of the memory buffer.