DISKBLOCKS(2)DISKBLOCKS(2)NAME
Diskblocks: Block, Disk, tempfile - temporary storage of variable-sized
blocks
SYNOPSIS
include "diskblocks.m";
diskblocks := load Diskblocks Diskblocks->PATH;
Block: adt {
addr: big; # address on file
n: int; # size in bytes
};
Disk: adt {
init: fn(fd: ref Sys->FD, gran: int, maxblock: int): ref Disk;
new: fn(d: self ref Disk, n: int): ref Block;
release: fn(d: self ref Disk, b: ref Block);
read: fn(d: self ref Disk, b: ref Block,
a: array of byte, n: int): int;
write: fn(d: self ref Disk, b: ref Block,
a: array of byte, n: int): ref Block;
};
init: fn();
tempfile: fn(): ref Sys->FD;
DESCRIPTION
Diskblocks manages a set of variable-sized blocks on a temporary file.
Init must be called before any other function in the module.
Each block has an address and a size in bytes, represented by a value
of type Block.
Each file is represented by the type Disk, providing the following
operations:
init(fd, gran, maxblock)
Initialises the file fd for use as temporary block storage and
returns a reference to a Disk to describe it. Fd must be open
for reading and writing, and must refer to a file that allows
random access. Blocks are allocated in multiples of the granu‐
larity gran, in bytes; the largest possible block is maxblock
bytes, which must be a multiple of gran.
d.new(n)
Allocate a block of n bytes on Disk d and return a reference to
it.
d.release(b)
Free the Block b, making it available for reallocation.
d.write(b, a, n)
Write n bytes from array a to Block b on Disk d, returning a
reference to the resulting Block. If b is nil or n exceeds b's
current size, write allocates a new block (releasing b). Thus
the returned value might differ from b, and must be used in sub‐
sequent IO requests.
d.read(b, a, n)
Read n bytes from Block b on Disk d into array a, returning the
number of bytes read. N must not exceed b.n.
Tempfile returns a file descriptor referring to a newly-created tempo‐
rary file, suitable for use by Disk.init. The file will be removed
automatically when the file descriptor is closed.
SOURCE
/appl/lib/diskblocks.b
DIAGNOSTICS
A function that returns an integer returns -1 on error; a function that
returns a reference returns nil on error. The system error string is
set in either case.
DISKBLOCKS(2)
