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Comment by Isinlor | Hacker News Reader

There is a garbage collection:

https://www.php.net/manual/en/features.gc.php

> This section explains the merits of the new Garbage Collection (also known as GC) mechanism that is part of PHP 5.3.

> First of all, the whole reason for implementing the garbage collection mechanism is to reduce memory usage by cleaning up circular-referenced variables as soon as the prerequisites are fulfilled. In PHP's implementation, this happens as soon as the root-buffer is full, or when the function gc_collect_cycles() is called. In the graph below, we display the memory usage of the script below, in both PHP 5.2 and PHP 5.3, excluding the base memory that PHP itself uses when starting up.

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PHP's garbage collector is ARC, unlike any other dynamic language that I know of.

ARC is more performant but can introduce memory leaks via circular references, which is probably not a big problem for short-lived scripts anyway.

Sounds optimal for PHP where 99% of scripts are short lived.

Which is perfect for a HTTP request.

I'm not sure if you did not read what I quoted, or I misunderstand something.

Yes, PHP has reference counting, but it also has specific process that kicks in to clean up circular references.

How is it more performant? If you have multiple threads than you will get serious atomic operation or other synchronization overhead.

PHP is share-nothing architecture. Nobody really uses threads in mainline PHP.

Whole class of problems around multi-threading, mutexes, dead locks etc. are really foreign to PHP developers.

Yeah, I should have mentioned that in the general case RC is not more performant (otherwise threaded managed languages would use it).

Python uses ARC plus a tracing GC for dealing with cycles, same as PHP: https://devguide.python.org/garbage_collector/

Perl uses ARC with no tracing GC, so you have to handle cycles yourself: https://www.perlmonks.org/?node_id=1173079

TCL uses ARC, and apparently doesn't need a tracing GC because it is impossible to create cycles in it: https://wiki.tcl-lang.org/page/Garbage+collection

ARC is not more performant, it's more deterministic. "regular" GCs have better throughput. RC in general also handles other resources (like files) a bit better than GC.

PHP has a GC since 2009 (version 5.3). Its goal is precisely to collect reference cycles.

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