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Allocate.md

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NAME

Allocate - allocate a block of memory

SYNOPSIS

    memoryBlock=Allocate(memHeader, byteSize)
    D0                   A0         D0

    void *Allocate(struct MemHeader *, ULONG);

Links: MemHeader

FUNCTION

This function is used to allocate blocks of memory from a given private free memory pool (as specified by a MemHeader and its memory chunk list). Allocate will return the first free block that is greater than or equal to the requested size.

All blocks, whether free or allocated, will be block aligned; hence, all allocation sizes are rounded up to the next block even value (e.g. the minimum allocation resolution is currently 8 bytes. A request for 8 bytes will use up exactly 8 bytes. A request for 7 bytes will also use up exactly 8 bytes.).

This function can be used to manage an application's internal data memory. Note that no arbitration of the MemHeader and associated free chunk list is done. You must be the owner before calling Allocate.

INPUTS

memHeader - points to the local memory list header. byteSize - the size of the desired block in bytes.

RESULT memoryBlock - a pointer to the just allocated free block. If there are no free regions large enough to satisfy the request, return zero.

EXAMPLE #include <exec/types.h> #include <exec/memory.h> void AllocMem(); #define BLOCKSIZE 4096L / Or whatever you want */

void main() { struct MemHeader *mh; struct MemChunk *mc; APTR block1; APTR block2;

/* Get the MemHeader needed to keep track of our new block */ mh = (struct MemHeader *) AllocMem((long)sizeof(struct MemHeader), MEMF_CLEAR ); if( !mh ) exit(10);

/* Get the actual block the above MemHeader will manage */ mc = (struct MemChunk *)AllocMem( BLOCKSIZE, 0L ); if( !mc ) { FreeMem( mh, (long)sizeof(struct MemHeader) ); exit(10); }

mh->mh_Node.ln_Type = NT_MEMORY; mh->mh_Node.ln_Name = "myname"; mh->mh_First = mc; mh->mh_Lower = (APTR) mc; mh->mh_Upper = (APTR) ( BLOCKSIZE + (ULONG) mc ); mh->mh_Free = BLOCKSIZE;

/* Set up first chunk in the freelist */ mc->mc_Next = NULL; mc->mc_Bytes = BLOCKSIZE;

block1 = (APTR) Allocate( mh, 20L ); block2 = (APTR) Allocate( mh, 314L ); printf("mh=$%lx mc=$%lxn",mh,mc); printf("Block1=$%lx, Block2=$%lxn",block1,block2);

FreeMem( mh, (long)sizeof(struct MemHeader) ); FreeMem( mc, BLOCKSIZE ); }

NOTE If the free list is corrupt, the system will panic with alert AN_MemCorrupt, $01000005.

SEE ALSO

Deallocate, exec/memory.h