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Hunsu
Hunsu

Reputation: 3381

Why sharing a static variable between threads reduce performance?

I asked question here and someone leaved a comment saying that the problem is I'm sharing a static variable.

Why is that a problem?

Upvotes: 1

Views: 764

Answers (2)

Nathan Hughes
Nathan Hughes

Reputation: 96385

The wiki static variable looks like a pretty substantial part of your program. Not knowing anything about what it's going or how it's coded, I would guess that it does locking in order to keep a consistent state. If most of your threads are spending their time blocking waiting to acquire access to this same object then that would explain why you're not seeing any gain from using multiple threads.

For threads to make a difference to the performance of your program they have to be reasonably independent, and not all locking on the same thing. The more locking they have to do, the less gain you will see. So try to split out the work so as much can be done independently as possible. For instance if there are work items that can be gathered independently, then you might be better off by having multiple threads go find the work items, then feed them to a queue that a dedicated thread can use to pull work items off the queue and feed them to the wiki object.

Upvotes: 1

Nitsan Wakart
Nitsan Wakart

Reputation: 2909

Sharing a static variable of and by itself should have no adverse effect on performance. Global data is common is all programs starting with the JVM and OS constructs.

Mutable shared data is a different story as the mutation of shared data can lead to both performance issues (cache misses at the very least) and correctness issues which are a pain and are often solved using locks, which lead to potentially other performance issues.

Upvotes: 2

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