[SOLVED] What is the name of the default memory allocator in Free Pascal?

[flowCRANE]

Free Pascal has a default memory allocator (or memory manager if you prefer) and its implementation is in the heaph.inc file. What kind of allocator is this? Any known algorithm, and if so, what is it called? I checked the documentation and even the sources, but unfortunately I did not find such information.

[jamie]

GetmemoryManager ?

It populates a TmemoryManager record you supply.

[flowCRANE]

No, that's not the point. The heaph.inc file contains the following functions:

Code: Pascal  [Select][+][-]

1. Function  SysGetmem(Size:ptruint):Pointer;
2. Function  SysFreemem(p:pointer):ptruint;
3. Function  SysFreememSize(p:pointer;Size:ptruint):ptruint;
4. Function  SysMemSize(p:pointer):ptruint;
5. Function  SysAllocMem(size:ptruint):Pointer;
6. function  SysTryResizeMem(var p:pointer;size:ptruint):Boolean;
7. Function  SysReAllocMem(var p:pointer;size:ptruint):Pointer;
8. function  SysGetHeapStatus:THeapStatus;
9. function  SysGetFPCHeapStatus:TFPCHeapStatus;

They are set as default in the memory manager:

Code: Pascal  [Select][+][-]

1. const
2.   MemoryManager: TMemoryManager = (
3.     NeedLock: false;  // Obsolete
4.     GetMem: {$ifndef FPC_NO_DEFAULT_HEAP}@SysGetMem{$else}nil{$endif};
5.     FreeMem: {$ifndef FPC_NO_DEFAULT_HEAP}@SysFreeMem{$else}nil{$endif};
6.     FreeMemSize: {$ifndef FPC_NO_DEFAULT_HEAP}@SysFreeMemSize{$else}nil{$endif};
7.     AllocMem: {$ifndef FPC_NO_DEFAULT_HEAP}@SysAllocMem{$else}nil{$endif};
8.     ReAllocMem: {$ifndef FPC_NO_DEFAULT_HEAP}@SysReAllocMem{$else}nil{$endif};
9.     MemSize: {$ifndef FPC_NO_DEFAULT_HEAP}@SysMemSize{$else}nil{$endif};
10.     InitThread: nil;
11.     DoneThread: nil;
12.     RelocateHeap: nil;
13.     GetHeapStatus: {$ifndef FPC_NO_DEFAULT_HEAP}@SysGetHeapStatus{$else}nil{$endif};
14.     GetFPCHeapStatus: {$ifndef FPC_NO_DEFAULT_HEAP}@SysGetFPCHeapStatus{$else}nil{$endif};
15.   );

They bodies are in the heap.inc file and contain application-side memory management code to minimize the use of the Windows HeapAlloc and HeapFree functions to increase allocation and deallocation efficiency. Is the code of these functions a port of some well-known allocator that has its own name and is described somewhere (such as mimalloc), or was it invented entirely by Free Pascal developers?

[Thaddy]

It was written from scratch by the FPC developers, but to a known, common pattern: bucketlist based allocators. The same pattern is e.g. used in Delphi too, with a completely different implementation based on FastMM. I have also seen implementations for C and C++, but in these languages the default is a simple heap based allocator. we can use that too: the implementation is in cmem.pas.
Bucket based allocators are less prone to heap memory fragmentation in the average use case.

In compiler shoot-outs, languages that have bucket based allocators usually have more efficient use of memory sizes, whereas heap based memory allocators favor speed over memory size.
a note of warning, though: the choice of a memory manager may depend on a specific use case.

[marcov]

Afaik the default FPC allocator also has per thread allocation/deallocation to avoid unnecessary locks.  That also has advantages and disadvantages, the positive is that allocating small amounts in a thread requires less locks, But it uses a bit more memory , and cross thread (allocate in one, deallocate in another) becomes more expensive.

[MarkMLl]

Afaik the default FPC allocator also has per thread allocation/deallocation to avoid unnecessary locks.  That also has advantages and disadvantages, the positive is that allocating small amounts in a thread requires less locks, But it uses a bit more memory , and cross thread (allocate in one, deallocate in another) becomes more expensive.

I believe you are correct, I remember discussing this with Jonas.

MarkMLl

[flowCRANE]

Ok, thanks for the answers. Is it described somewhere so that I can learn how exactly this implementation works?

[PascalDragon]

Is it described somewhere so that I can learn how exactly this implementation works?

If you want to learn how it works, look at the source code.

[flowCRANE]

What else is left if there is no documentation. Thanks.

[Thaddy]

Well, the internals, read the sourcecode, the design pattern and theory: google on bucket based memory allocation.
What else is not documented? Bloody irritating since I already explained it.