PHP Features Garbage Collection Mechanism 2 - Recycling Cycle

Traditionally, the reference counting memory mechanism used in PHP cannot handle circular reference memory leaks. However, 5.3.0 PHP uses the synchronization algorithm in the article » Concurrent Cycle Collection in Reference Counted Systems to deal with this memory leak problem.
A complete description of the algorithm is somewhat beyond the scope of this section, and only the basics will be introduced. First, we need to establish some basic rules. If a reference count is increased, it will continue to be used and of course no longer in the garbage. If the reference count is reduced to zero, the variable container will be cleared (free). That is, a garbage cycle occurs only when the reference count decreases to a non-zero value. Secondly, during a garbage cycle, find out which parts are garbage by checking whether the reference count is reduced by 1 and checking which variable containers have zero references.

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