Matthew Fonda on :
Very cool, glad to see it finally made it into PHP 
|
Saturday, June 4. 2005Compiler Halt Patch, is in!
A few months ago I proposed a patch that would permit stopping the Zend Parser at a certain point in the script and not having it try to examine any subsequent content. The logic behind this feature was to simplify the process of creating single-script installers, such as the one used by FUDforum. The installer is a single script that at the end of it contains a code archive of the application being installed, which the installation process places into the set locations. The problem with implementing such installer at this point was that the data must be made PHP safe, so no <?php or similar "start-php-context" tokens that may be present in the archive are not treated as such resulting in undesired code execution. The solution required either encoding of the data using base64, making it 30% large or custom encoding scheme that would “hide” anything resembling a PHP start tag. Even with this problem solved, one last issue remained, this being the memory limit. Since the Zend Parser takes the entire script it needs to allocate memory for storing the archive that can be several megabytes large, this allocation quickly exhausts the default 8meg limit and causes a fatal out-of-memory error. By gaining the ability to stop the parser, this can be avoided since the data beyond the stoppage point will not be examined.
The main downside of the originally proposed patch was it provided no easy way to determine where does the archive portion of the file starts. The developer would need to parse their own script looking for the “STOP” point to determine the end of the script and the start of the archive. Given an overwhelming support for this feature, Zeev Suraski decided to rewrite the patch to include an easy way to determine this position. After some hacking on Zeev’s part and a fair bit of testing on mine a new patch was created and today applied to CVS. The patch provides a __HALT_COMPILER() construct that can be used to stop the parser and a __COMPILER_HALT_OFFSET__ constant indicating the “script-end” position. Here is a brief example of it’s usage: PHP: Output: some archive data, which can be binary The output of the code will be just the archive data, which can now be fetched without having to manually look for the "stop" portion inside the file. Kudos to Zeev for taking the time to improve on my idea and developing this patch, which as of today is part of PHP 5.1. Comments
Display comments as
(Linear | Threaded)
András Bártházi on :
But why is looks like a function? If - as I guess - it's not a real function, why does it looks like that? It's bad, I think novice programmers will often try to use it in the middle of their code, as a synonim to exit.
And I'm against the name of it, too. I understand, that from the PHP language developer's point of view it halts the compiler. But the PHP programmer's view, it signs the end of the code, and the start of the data. Perl's __DATA__ is more nicer, but if you don't want to copy it, you can use __CODE_END__ or something like this. It's seems to me an adhoc implementation, not a well planned one. Anyway, it's a nice feature, and I think it will be very useful for us. Ilia Alshanetsky on :
The reason it looks like a function is to reduce the likelihood of a name conflict with a pre-defined user constant.
As far as misuse of the feature, people will always find to misuse functionality no matter how simple or complex it is. Designing a language for the lowest common dominator, which for PHP is quite low, would pretty much cripple the language. R. Rajesh Jeba Anbiah on :
I'm kinda lost here. Does it mean that file_get_contents() previously/now parses PHP codes (I believe not). Is this feature also implemented with include()/require()?
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||
Jacques Marneweck's Blog on : PHP Compiler Halt Patch