On 22.01.2022 at 17:18, Rowan Tommins wrote: > On 22/01/2022 15:30, Christoph M. Becker wrote: > >> If you trigger the garbage collector manually (i.e. call >> gc_collect_cycles() after unset($callback)), the loop terminates right >> away. I'm not sure why it doesn't without manually triggering the GC. > > Most values are freed as soon as their refcount reaches zero, which > obviously won't happen for circular references, so an additional > algorithm is needed for those. This "cycle collection" algorithm is > relatively expensive, so doesn't run every time a possible candidate is > found, but only when a list of candidates reaches a particular > threshold. The algorithm is outlined in the manual, although it looks > like the constant 10000 mentioned there has been replaced by an adaptive > threshold (which can be inspected with gc_status()): > https://www.php.net/manual/en/features.gc.collecting-cycles.php > > If you measure memory usage while running the example code in a loop, > you should see it slowly growing and then periodically dropping each > time a cycle collection is run. That's why gc_collect_cycles() exists - > if you _know_ you've created circular references, you can tell the > engine to find and free them immediately, rather than waiting for the > next pass.
Ah, right. Thanks Rowan! Christoph -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: https://www.php.net/unsub.php
