<?php

function safeopen ($filename, &$errmsg, $mode  = 'r', $lock = LOCK_EX) {

	# Safely opens a file, including file locking and error reporting.
	# Pass it the name of the file you want to open, plus a variable
	# to put error messages into (plus, optionally, the file read/write
	# mode and the lock mode); the function will pass back a file-
	# handle on success, or return false and put an error string in
	# the error-message variable.
	
	# If the file is locked on the first attempt, this function will
	# automatically retry it every $retry_msecs milliseconds, until
	# $timeout_secs seconds have elapsed.
	
	# The flock() mode automatically gets LOCK_NB added to it, so 
	# don't include that in your function call.
	
	$retry_msecs = 250;
	$timeout_secs = 5;
	
	global $php_errormsg;
	
	$elapsed = 0;
	while (! $fh) {
		# This will always fail the first time around.
		if ($elapsed >= $timeout_secs * 1000) {
			if (strlen($errmsg)) {
				$errmsg = "Couldn't open file: ".$errmsg;
			} else {
				$errmsg = "Couldn't open file; no other error data available.";
			}
			return false;
		}
		$fh = @fopen($filename, $mode);
		if (! $fh) {
			$errmsg = $php_errormsg;
			usleep($retry_msecs * 1000);
			$elapsed += $retry_msecs;
		}
	}
	
	while (! @flock($fh, $lock+LOCK_NB)) {
		$errmsg = $php_errormsg;
		if ($elapsed >= $timeout_secs * 1000) {
			if (strlen($errmsg)) {
				$errmsg = "Couldn't acquire lock on file: ".$errmsg;
			} else {
				$errmsg = "Couldn't acquire lock on file.";
			}
			# Close the filehandle anyway. Eliminates possibility of
			# resource starvation if script continues for a long time
			# after failing to flock() the file.
			fclose($fh);
			return false;
		}
		usleep($retry_msecs * 1000);
		$elapsed += $retry_msecs;
	}
	return $fh;
}

?>