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javamultithreadingthread-local
Sriharsha g.r.v
Sriharsha g.r.v

Reputation: 510

When should one prefer ThreadLocal over synchronization, apart from for the performance improvement?

When should one prefer ThreadLocal over synchronization, apart from for the performance improvement? Please explain using a real life example.

Upvotes: 4

Views: 3735

Answers (4)

Solomon Slow
Solomon Slow

Reputation: 27115

ThreadLocal is not an alternative to synchronized. The main problem solved by ThreadLocal is how to manage per-thread static data in an application.

static is something that you should try to avoid whenever you can: It's a recipe for un-testable, brittle code.

Upvotes: 3

Adelin
Adelin

Reputation: 18941

When you use ThreadLocal variables these are seen and manipulated by the thread using it ONLY, no other thread can see them. Thread local variables dies when the thread does too. And one should be careful then using ThreadLocal variables when using thread pools.

ThreadLocal variables are put in a special memory space called Thread private stack.

Shared variable are put in the heap memory space where they are shared among all threads and they are either synchronized or not.

So it is more about use case than performance.

One can use ThreadLocal variable to hold a connection to some DB where the connection is associated with the current thread ONLY and no need for other thread to see it and a need to synchronize it. The cache - a shared in memory map or list,for example, however, is shared among all threads in a server application and it must be synchronized.

Upvotes: 3

earthling
earthling

Reputation: 69

ThreadLocal provides global variable access with in a Thread. This will help when you want to share a variable across methods and still retain Thread scope.

J2EE application servers use ThreadLocal for tracking Transaction, Security context with out passing around

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533442

The only reason to use Threads is for performance reasons (or perhaps you like confusion ;).

AFAICS If you discount performance, there is not reason to use Threads, ThreadLocal nor synchronzied.

Upvotes: 0

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