NAME

qmalloc – quickfit malloc malloc, mallocz, smalloc, realloc, calloc, free, msize, setmalloctag, setrealloctag, getmalloctag, getrealloctag, mallocinit, mallocsummary – quickfit kernel memory allocator

SYNOPSIS

void* malloc(usize size)
void* mallocalign(usize size, usize align, long offset, usize span)
void* mallocz(usize size, int clr)
void* smalloc(usize size)
void* realloc(void *p, usize size)
void* calloc(usize n, usize szelem)
void    free(void *ptr)
usize msize(void *ptr)
void    setmalloctag(void *ptr, uintptr tag)
uintptrgetmalloctag(void *ptr)
void    setrealloctag(void *ptr, uintptr tag)
uintptrgetrealloctag(void *ptr)
void    mallocinit(void) void    mallocsummary(void)

DESCRIPTION

These are kernel versions of the functions in malloc(2). They allocate memory with Quickfit with an allocator from Kernighan & Ritchie. The allocation is currently fixed, but could call physalloc(9nix) in the future. All but smalloc (which calls sleep(9)) may safely be called by interrupt handlers.
Malloc returns a pointer to a block of at least size bytes, initialised to zero. The block is suitably aligned for storage of any type of object. The call malloc(0) returns a valid pointer rather than null. Mallocz is similar, but only clears the memory if clr is non–zero.
Smalloc returns a pointer to a block of size bytes, initialised to zero. If the memory is not immediately available, smalloc retries every 100 milliseconds until the memory is acquired.
Mallocalign allocates a block of at least n bytes of memory respecting alignment contraints. If align is non–zero, the returned pointer is aligned to be equal to offset modulo align. If span is non–zero, the n byte block allocated will not span a span–byte boundary.
Realloc changes the size of the block pointed to by p to size bytes, if possible without moving the data, and returns a pointer to the block. The contents are unchanged up to the lesser of old and new sizes, and any new space allocated is initialised to zero. Realloc takes on special meanings when one or both arguments are zero:
realloc(0, size)
means malloc(size); returns a pointer to the newly–allocated memory
realloc(ptr, 0)
means free(ptr); returns null
realloc(0, 0)
no–op; returns null
Calloc returns a pointer to a block of memory of at least n*szelem bytes, initialised to zero. New code should use mallocz instead.
The argument to free is a pointer to a block of memory allocated by one of the routines above, which is returned to the allocation pool, or a null pointer, which is ignored.
When a block is allocated, sometimes there is some extra unused space at the end. Msize grows the block to encompass this unused space and returns the new number of bytes that may be used.
The memory allocator does not maintain ``malloc tag'' and the ``realloc tag'', but the functions setmalloctag, getmalloctag, setrealloctag, and getrealloctag are provided for compaibility with the pool(2) library.
Mallocinit must be called before malloc is used. Mallocsummary prints a short summary of the allocator's state on the console.

SOURCE

/sys/src/9/port/qmalloc.c
/sys/src/nix/port/qmalloc.c

DIAGNOSTICS

All functions except smalloc return a null pointer if space is unavailable.

SEE ALSO

The C Programming Language, 2ed, Brian Kernighan and Dennis Ritchie, chapter 8 §7: Example—Storage Allocator.
Quickfit: An efficient algorithm for heap storage allocation" , Charles B. Weinstock and William A. Wulf. ACM SIGPLAN Notices, 23(10):141—144, October 1988.
pool(2), physalloc(9nix)