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I have a class which has:
Lets assume that multiple concurrent invocation of all methods are possible. I need to achieve thread-safety while maximising performance.
Approach1 (extremely slow) - Declare field-types as ArrayList and use synchronise keyword on all methods.
Approach2 - Declare field-type as CopyOnWriteArrayList and synchronise the mutating method.
Questions
463
asked Aug 20 '15 15:08
The collection classes that are thread-safe in Java are Stack, Vector, Properties, Hashtable, etc.
Given the structure of the JVM, local variables, method parameters, and return values are inherently "thread-safe." But instance variables and class variables will only be thread-safe if you design your class appropriately.
To make these classes thread-safe, you must prevent concurrent access to the internal state of an instance by more than one thread. Because Java was designed with threads in mind, the language provides the synchronized modifier, which does just that.
A thread-safe variant of ArrayList in which all mutative operations (e.g., add, set, remove..) are implemented by creating a separate copy of an underlying array. It achieves thread safety by creating a separate copy of the List which is different than vector or other collections used to provide thread-safety.
Do you need the random access offered by an ArrayList? Can you instead use a thread-safe ordered collection like ConcurrentSkipListSet (non-blocking) or PriorityBlockingQueue (blocking)? Both have log(n) insertions.
Mutation methods in both cases are thread-safe.
Edit: Just note, you would still run into atomicity concerns. If you need the add's to be done attomically then you would need more coarse locking.
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