Shared memory allocator

Created: 7.96
Modified: 5.97

Synopsis

#include <sys/types.h> #include "shmalloc.h" void* shmcreate (char* path, char ch, int nKB, mode_t mode, int off, int* id); void* shmattach (int shmid, void* addr); void shmlocate (int shmid, void* addr); void* shmalloc (int nbytes); void shmfree (void*); void* shmemdup (void* mem, int nbytes); void shmstat (FILE*); /* prints allocation map to file */

Description

Shmcreate creates a shared memory segment. Path and ch are used to generate the Unix key (see ftok(3)). Mode sets the rwx permission bits. Off defines the offset in the shared memory segment from where the dynamic allocation begins, so that space can be reserved for static data at the head of the shared memory.

Shmattach grabs access to existing shared memory. The address is passed as argument to the shmat system call.

Shmlocate is used to initialize the allocator library in a newly loaded module (see load(2)). It should be called with the correct id and address preferably by the entry point function of the loaded module. The initialization is necessary because the allocator is not a shared library.

Files

shmalloc.h C header
libshmalloc.a AIX4.1 shared library (-lshmalloc)
shmalloc.exp Exported symbols (-bI:shmalloc.exp)
shmcreate.c Example
shmstat.c Example

Caveat

Works correctly, and is good enough for prototype software. No claims made as to efficiency.
Not all addresses are valid on AIX for attaching shared memory segments, and not many segments are allowed anyway. (But that's to do with AIX, not my library.)