err is now always set to null when doing a new operation.
previously, if the same var was used multiple times and a previous one failed,
code might think that a previous error belonged to the current operation.
Weak comparisons were used in cases when we were worried about comparing int and float.
In some cases (particularly involving Vector3) we do need to be wary of this, so floatval() is used to avoid incorrect type comparisons.
In other cases, we were already exclusively comparing float-float, so weak compare wasn't needed anyway.
this reduces memory footprint slightly, but more importantly reduces GC workload.
Since it also reduces the work done on cache hit, it might *slightly* improve performance,
but any improvement is likely to be minimal.
this reduces the risk of OOM during conversion of large worlds
we probably ought to limit the size of region caches for regionized worlds, but that's a problem for another time.
GC is not required for RakLib as it doesn't generate any unmanaged cycles.
Cycles in general do exist (e.g. Server <-> ServerSession), but these are
explicitly cleaned up, so GC wouldn't have any useful work to do.
This has been a long-standing issue since at least 2016, and probably longer.
Heavy use of getBlock(At) could cause the cache to blow up and use all available memory.
Recently, it's become clear that unmanaged cache size is also a problem for GC, because
the large number of objects blows up the GC root buffer. At first, this causes more frequent
GC runs; later, the frequency of GC runs drops, but the performance cost of them goes up
substantially because of the sheer number of objects. We can avoid this by trimming the
cache when we detect that it's exceeded limits.
I've implemented this in such a way that failing to update blockCacheSize in new code
won't have lasting impacts, since the cache count will be recalculated during scheduled
cache cleaning anyway.
Closes#152.
No one in their right mind is going to change the defaults for these anyway.
All this crap does is overwhelm users with stuff they don't understand.
Most of this stuff has no business being modified by non-developers anyway.
This PR replicates the mechanism by which PHP's own GC is triggered: using a dynamically adjusted threshold based on the number of roots and the number of destroyed cycles. This approach was chosen to minimize behavioural changes.
This currently only applies to the main thread. Doing this for other threads is a bit more complicated (and in the case of RakLib, possibly not necessary anyway).
By doing this, we can get more accurate performance profiling. Instead of GC happening in random pathways and throwing off GC numbers, we trigger it in a predictable place, where timings can record it.
This change may also produce minor performance improvements in code touching lots of objects (such as `CraftingDataPacket` encoding`), which previously might've triggered multiple GC runs within a single tick. Now that GC runs wait for `MemoryManager`, it can touch as many objects as it wants during a tick without paying a performance penalty.
While working on this change I came across a number of issues that should probably be addressed in the future:
1) Objects like Server, World and Player that can't possibly be GC'd repeatedly end up in the GC root buffer because the refcounts fluctuate frequently. Because of the dependency chains in these objects, they all drag each other into GC, causing an almost guaranteed parasitic performance cost to GC. This is discussed in php/php-src#17131, as the proper solution to this is probably generational GC, or perhaps some way to explicitly mark objects to be ignored by GC.
2) World's `blockCache` blows up the GC root threshold due to poor size management. This leads to infrequent, but extremely expensive GC runs due to the sheer number of objects being scanned. We could avoid a lot of this cost by managing caches like this more effectively.
3) StringToItemParser and many of the pocketmine\data classes which make heavy use of closures are afflicted by thousands of reference cycles. This doesn't present a major performance issue in most cases because the cycles are simple, but this could easily be fixed with some simple refactors.
