Not so long ago I posted to comp.lang.php to raise the discussion about
thread safety of accessing files with domxml_open_file() (and also other
extension specific file-accessing functions). No one replied but I
wanted to know if it was safer to suck the data into memory while using
flock() on the file so that there was no (less?) danger of getting dirty
reads/writes if the file was being accessed from concurrently running
scripts.

Of course, using flock() means that you actually have to load the file
into memory first which is obviously bad given your evidence (even when
not using file() and putting it in a very large hash first).

I'm wandering if it is neccesary to use flock() on ALL filesystem
interactions in a web based (multi-threaded) application.

Yes, that's necessary, and not only in multithreaded applications, also
in multi-process applications like the Apache webserver. But those
questiosn really belong on the php-general@lists.php.net mailinglist.

Derick

--
"my other box is your windows PC"

Derick Rethans http://derickrethans.nl/
PHP Magazine - PHP Magazine for Professionals http://php-mag.net/

I'm wandering if it is neccesary to use flock() on ALL filesystem
interactions in a web based (multi-threaded) application.

flock and fcntl predate the multi-threaded approach on Unix
and as such they have process granularity, i.e. they won't
help in multi-threaded environments.

- Sascha

I'v already started developing an object wrapper to DOM XML for my own
usage (but freely available to anyone as with all my stuff) which
provides a central point where I can control the way all this file
accessing is done.

Here is the constructor method alone plus the constant definitions
preceeding the class. This code has not been tested yet.

 /**
 * Constructor method
 *
 * Create the objDoc instance property and associated ndRoot 

property based
* on the user-selected mode of document creation. In the process,
establish
* the blnIsReadOnly property.
*
* @param mixed information required to create a DOM document
* @param int constant specifying how the document is to be
created
* @return void
*/
function domDoc(&$Starter,$intUse = DOMDOC_AS_NEW) {
$this->objErr = new xmlErrorLog($this);
$this->intMode = $intUse;
$this->blnIsReadOnly = true;
// for more info on each case
block, see
// comments in the constant definitions
// at the top of this file.
switch ($intUse) {
case DOMDOC_AS_NEW:
$this->blnIsReadOnly = false;
$this->objDoc = domxml_new_doc("1.0");
$elRoot = $this->objDoc->create_element($Starter);
$this->ndRoot = $this->objDoc->append_child($elRoot);
break;
case DOMDOC_AS_READFILE:
$fp = fopen($Starter,"r")
OR $this->objErr->throw(
"could not open ".$Starter." for reading."
);
// attempt thread safety by using flock
flock($fp,LOCK_SH);
$xmlData = fread($fp,filesize($Starter));
flock($fp,LOCK_UN);
fclose($fp);
// finish working with the file as
// quickly as possible and THEN worry
// about making a DOM doc from it.
$this->_domOpenFromData($xmlData);
break;
case DOMDOC_AS_WRITEFILE:
$this->blnIsReadOnly = false;
$this->fp = fopen($Starter,"bw+")
OR $this->objErr->throw(
"could not open ".$Starter." for writing."
);
flock($this->fp,LOCK_EX);
$xmlData = fread($this->fp,filesize($Starter));
$this->_domOpenFromData($xmlData);
break;
case DOMDOC_AS_REMOTEFILE:
$fp = fopen($Starter,"r")
OR $this->objErr->throw(
"could not open ".$Starter." for reading."
);
$xmlData = fread($fp,filesize($Starter));
fclose($fp);
$this->_domOpenFromData($xmlData);
break;
case DOMDOC_AS_REFERENCE:
$this->objDoc =& $Starter;
break;
case DOMDOC_AS_DATA:
$this->_domOpenFromData($Starter);
break;
default:
$this->objErr->throw(
"second argument to domDoc constructor is invalid"
);
}
}