![]() Incremental, concurrent, and real-time garbage collectors address these problems, with varying trade-offs. Unpredictable stalls can be unacceptable in real-time environments, in transaction processing, or in interactive programs. ![]() The moment when the garbage is actually collected can be unpredictable, resulting in stalls (pauses to shift/free memory) scattered throughout a session. The impact on performance was given by Apple as a reason for not adopting garbage collection in iOS, despite it being the most desired feature. Interaction with memory hierarchy effects can make this overhead intolerable in circumstances that are hard to predict or to detect in routine testing. The comparison however is made to a program generated by inserting deallocation calls using an oracle, implemented by collecting traces from programs run under a profiler, and the program is only correct for one particular execution of the program. A peer-reviewed paper from 2005 concluded that GC needs five times the memory to compensate for this overhead and to perform as fast as the same program using idealised explicit memory management. Therefore, the penalty for the convenience of not annotating object lifetime manually in the source code is overhead, which can impair program performance. GC uses computing resources to decide which memory to free.
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