ref: a411870ee4640241e3c494367d922847da84f972
dir: /man/2/iobuf/
.TH IOBUF 2
.SH NAME
iobuf: ReadBuf, WriteBuf \- read/write buffers
.SH SYNOPSIS
.EX
include "iobuf.m";
iobuf: IOBuf;
ReadBuf, WriteBuf: import iobuf;
iobuf = load IOBuf IOBuf->PATH;
init: fn();
ReadBuf: adt{
new: fn(fd: ref Sys->FD, bufsize: int): ref ReadBuf;
newc: fn(queuesize, bufsize: int): ref ReadBuf;
setsep: fn(r: self ref ReadBuf, sep: string, strip: int);
reads: fn(r: self ref ReadBuf): array of byte;
readn: fn(r: self ref ReadBuf, n: int): array of byte;
fill: fn(r: self ref ReadBuf, data: array of byte, wc: Sys->Rwrite);
}
WriteBuf: adt{
new: fn(fd: ref Sys->FD, bufsize: int): ref WriteBuf;
newc: fn(bufsize: int): ref WriteBuf;
write: fn(w: self ref WriteBuf, buf: array of byte);
flush: fn(w: self ref WriteBuf);
eof: fn(w: self ref WriteBuf);
request: fn(w: self ref WriteBuf, n: int, rc: Sys->Rread);
}
.EE
.SH DESCRIPTION
.PP
This module provide simpler and faster alternative to
.IR bufio (2).
On reading text file it's about 30-40 times faster than bufio,
on writing text file it's about 3-4 times faster than bufio.
.PP
.B init
must be called before invoking any other operation of the module.
.SS ReadBuf
.PP
ReadBuf is used when we receive stream of bytes (from fd or
file2chan for ex.) while we need to read by full records (either
separated by some delimiter or having known size).
.PP
Reading from ReadBuf is blocking operation.
.PP
.B setsep
convert
.I sep
from string to array of byte, and
.B reads
will use
that array to search for separator.
If separator will be Unicode char which may be encoded with different
sequences of bytes,
.B reads
may fail to find it.
.PP
.B reads
return record separated by
.IR sep ,
optionally with separator
stripped from end of record.
Last record may not end with separator, so ReadBuf can't distinguish
between incomplete record because of unexpected EOF and full last record
without separator.
Will return nil on EOF.
Will raise on I/O error.
Will raise if neither
.I sep
nor EOF will be found in
.I bufsize
bytes.
.PP
.B readn
return record with
.I n
bytes size, or less on EOF.
It's possible to have
.I n
greater than
.IR bufsize .
Will return array with less than
.I n
bytes on EOF.
Will return nil on EOF.
Will raise on I/O error.
.PP
Arrays returned by
.B reads
and
.B readn
usually will be slices of
ReadBuf's internal buffer, which may be overwritten on next
.B reads
or
.B readn
calls, so these calls may change contents of
previously returned arrays.
.PP
When ReadBuf used with chan instead of fd,
.I queuesize
define
maximum amount of packets (not bytes!) received from chan, which
wasn't fetched yet by
.B reads
or
.BR readn .
This is needed to optimize latency.
.PP
When ReadBuf used with chan, while one process may block in
.B reads
or
.BR readn ,
another may receive data from chan, and
should call
.B fill
to put this data into ReadBuf.
.PP
.B fill
will either immediately send reply to
.I wc
if it was able
to add data to ReadBuf, or save pending
.I data
and
.I wc
in
ReadBuf (reply to
.I wc
will be sent later from process
calling
.B reads
or
.BR readn ).
Call to
.B fill
never blocks.
Will send error "concurrent writes not supported" to
.I wc
and drop
.I data
if will be called again before reply to
previous
.I wc
will be sent (i.e. when previous
.I wc
is in
pending state because of full incoming queue).
.PP
Resume:
.RS
.IP •
Process reading from ReadBuf doesn't need to know about
data source (fd or chan).
.IP •
Process reading from ReadBuf may intermix reads() and
readn(), may change record separator at any time.
.IP •
Process reading from ReadBuf receive nil on EOF or got
exception on I/O error.
.IP •
Process receiving data from chan (usually, file2chan) for
ReadBuf just call fill() and don't bother about errors or
replying to
.IR wc .
.RE
.PP
Limitations:
.RS
.IP •
Unicode separator may not be detected in some cases.
.IP •
Offset/seek doesn't supported (so offset received with
file2chan request will be ignored).
.IP •
No getb(), getc(), ungetb(), ungetc() - but they can be
added later.
.IP •
Only one process may call reads() or readn() and only one
(another) process may call fill().
.RE
.SS WriteBuf
.PP
WriteBuf is used when we sending stream of bytes (to fd or
file2chan for ex.) while we want to write data by (possibly
small) records.
.PP
Writing to WriteBuf is blocking operation.
.PP
.B write
is adding data from
.I buf
to WriteBuf. Size of
.I buf
may
be greater than
.IR bufsize .
It may call
.BR flush .
Will raise on I/O error.
.PP
.B flush
ensure all buffered data in WriteBuf is actually written.
Will raise on I/O error.
.PP
When WriteBuf used with chan, while one process may block in
.B write
or
.BR flush ,
another may receive read request from chan,
and should call
.B request
to let
.B write
or
.B flush
send data from
WriteBuf to chan when they'll be ready.
.PP
.B eof
calls
.BR flush ,
but what it does next depends on WriteBuf type.
When WriteBuf used with fd, it do nothing more and just returns.
When WriteBuf used with chan, it'll wait for next
.B request
and will reply
on all with EOF
.BI ( "" nil "" , "" nil "" )
, and will returns only after got
.B request
with
.B nil
.IR rc .
.PP
.B request
notified WriteBuf about data requested by chan, to let
.B write
or
.B flush
to send data from
.I buf
to chan.
Call to
.B request
never blocks.
Will send error "concurrent reads not supported" to
.I rc
if will be called again before reply to previous
.I rc
will
be sent.
.PP
Resume:
.RS
.IP •
Process writing to WriteBuf doesn't need to know about
data destination (fd or chan).
.IP •
Process writing to WriteBuf got exception on I/O error.
.IP •
Process receiving read requests from chan (usually, file2chan)
from WriteBuf just call request() and don't bother about errors
or replying to
.IR rc .
.RE
.PP
Limitations:
.RS
.IP •
Offset/seek doesn't supported (so offset received with
file2chan request will be ignored).
.IP •
Only one process may call write() or flush() and only one
(another) process may call request().
.RE
.SH EXAMPLES
.EX
.EE
.SH SOURCE
.PP
.B /appl/lib/iobuf.b
.br
.SH SEE ALSO
.PP
.IR bufio (2)
.SH BUGS