Edit report at http://bugs.php.net/bug.php?id=35090&edit=1
ID: 35090
User updated by: askalski at gmail dot com
Reported by: askalski at gmail dot com
Summary: file i/o is not buffered
Status: Bogus
Type: Bug
Package: Filesystem function related
Operating System: linux
-PHP Version: 5CVS-2005-11-03 (snap)
+PHP Version: 5.3.3
Block user comment: N
New Comment:
I guess that's one way to deal with it. At least then it would be clear
to PHP developers that each fwrite() makes a separate system call.
Even better would be for PHP to use the C stdio library for file i/o,
and take advantage of the buffering it offers by default. Even back in
the 1970's when C was created, they had already figured out that
buffered I/O was a good thing, and consequently built it into stdio...
(I'm surprised to see feedback on a bug ticket that was closed as
"Bogus" almost five years ago. Ultimately, this is pretty low on my
list of "reasons PHP execution is so painfully slow"; it's just
something I spotted when doing an strace to troubleshoot an unrelated
issue. That's why I never bothered to pursue it further.)
Previous Comments:
------------------------------------------------------------------------
[2010-08-12 12:59:41] surfchen at gmail dot com
So we need to add a note on the documentation say that this function not
supported
with filesystem wrapper, right?
------------------------------------------------------------------------
[2005-11-03 23:40:24] askalski at gmail dot com
> instead it uses the system's file io buffering function
> to set the buffer.
Assuming you're talking about setvbuf() and not kernel
level write-behind caching, this statement is false.
The file is opened by _php_stream_fopen():
fd = open(realpath, open_flags, 0666);
(It is never subsequently wrapped with fdopen())
At this point, the stream is not buffered at all.
When I later call stream_set_write_buffer(), it hits
php_stdiop_set_option():
case PHP_STREAM_OPTION_WRITE_BUFFER:
if (data->file == NULL) {
return -1;
}
/* setvbuf happens down here */
Because there is no FILE* handle (data->file), setvbuf()
is never called for the stream.
One of either the documentation
(http://us3.php.net/stream_set_write_buffer)
or the PHP source is wrong.
------------------------------------------------------------------------
[2005-11-03 21:34:16] [email protected]
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php
PHP does not do any buffering itself, instead it uses the system's file
io buffering function to set the buffer.
There is already a feature request open to enable in-php buffering.
------------------------------------------------------------------------
[2005-11-03 21:29:08] [email protected]
Can you please answer why this is not a bug Wez? I forgot the reason :)
------------------------------------------------------------------------
[2005-11-03 19:16:09] askalski at gmail dot com
Description:
------------
The documentation for stream_set_write_buffer() says that fwrite()s are
buffered at 8K by default. In reality, it does not buffer at all. Any
attempt to call stream_set_write_buffer() on a regular file handle
results in failure.
Reproduce code:
---------------
$fh = fopen("asdf", "w");
// write some data using the default buffering
for ($i = 0; $i < 5; $i++)
fwrite($fh, "test");
// demonstrate that stream_set_write_buffer fails
$n = stream_set_write_buffer($fh, 8192);
if ($n != 0)
echo "stream_set_write_buffer failed\n";
// write some more data to demonstrate the failure
for ($i = 0; $i < 5; $i++)
fwrite($fh, "again");
fclose($fh);
Expected result:
----------------
PHP should buffer its I/O, and strace should log a single write().
stream_set_write_buffer() should not fail on regular files.
Actual result:
--------------
Output:
stream_set_write_buffer failed
Abridged strace output:
open("/tmp/php5-200511031730/asdf", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
fstat64(3, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
lseek(3, 0, SEEK_CUR) = 0
write(3, "test", 4) = 4
write(3, "test", 4) = 4
write(3, "test", 4) = 4
write(3, "test", 4) = 4
write(3, "test", 4) = 4
write(1, "stream_set_write_buffer failed\n", 31) = 31
write(3, "again", 5) = 5
write(3, "again", 5) = 5
write(3, "again", 5) = 5
write(3, "again", 5) = 5
write(3, "again", 5) = 5
close(3) = 0
------------------------------------------------------------------------
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Edit this bug report at http://bugs.php.net/bug.php?id=35090&edit=1
