Diskblocks: Block, Disk, tempfile - temporary storage of variable-sized blocks .EX 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; 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: .TF 8n

init( fd\f5, gran\f5, 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 granularity 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\f5, a\f5, 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 subsequent IO requests.

d .read( b\f5, a\f5, 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 temporary file, suitable for use by Disk.init . The file will be removed automatically when the file descriptor is closed.

/appl/lib/diskblocks.b 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.