Edit report at http://pear.php.net/bugs/bug.php?id=18618&edit=1
ID: 18618
Updated by: [email protected]
Reported By: andy at fud dot org dot nz
Summary: Incorrect CHUNK_SIZE
Status: Assigned
Type: Bug
Package: Crypt_GPG
Operating System: BSD/Linux
Package Version: SVN
PHP Version: Irrelevant
Assigned To: gauthierm
Roadmap Versions:
New Comment:
Andy, thanks for your detailed report.
When developing the file streaming operations for Crypt_GPG I tested a
lot using
strace to see what the buffer size used by PHP is. It seems PHP always
reads in 8k
chunks no matter what chunk size you specify. If you specify 4k chunks,
PHP reads
one 8k chunk and the next read comes from an internal buffer in PHP.
Of course, this may be different for writes.
Your description certainly sounds correct and I will have to do more
testing to
verify PHP itself works properly.
Previous Comments:
------------------------------------------------------------------------
[2011-06-20 17:20:21] gauthierm
-: [email protected]
+: andy at fud dot org dot nz
-Assigned To:
+Assigned To: gauthierm
------------------------------------------------------------------------
[2011-06-20 17:19:09] gauthierm
Description:
------------
"POSIX.1-2001 says that write(2)s of less than PIPE_BUF bytes must be
atomic: the output data is written to the pipe as a contiguous
sequence.
Writes of more than PIPE_BUF bytes may be non-atomic: the kernel may
interleave the data with data written by other processes."
Most operating systems have PIPE_BUF as 4096 bytes. Setting CHUNK_SIZE
to
8192 may cause php to do two 4k writes which can cause Crypt_GPG to
hang
forever.
It hangs because $fdInput is returned as writable by stream_select(),
the
first 4k write succeeds (fully or partially) but because php will try
to
write the next 4k chunk it hangs as the fd is full and hasn't beed
re-selected to test if it can be written.
The other option is to set all file descriptors as non-blocking using
stream_set_blocking(), the code correctly increments the buffers for
the
actual amount written/read.
This will also fix bug 18526
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