Thread Confinement

by

So when an object is confined to a thread, no other thread can have access to it?

No, it’s the other way around: if you ensure that no other thread has access to an object, then that object is said to be confined to a single thread.

There’s no language- or JVM-level mechanism that confines an object to a single thread. You simply have to ensure that no reference to the object escapes to a place that could be accessed by another thread. There are tools that help avoid leaking references, such as the ThreadLocal class, but nothing that ensures that no reference is leaked anywhere.

For example: if the only reference to an object is from a local variable, then the object is definitely confined to a single thread, as other threads can never access local variables.

Similarly, if the only reference to an object is from another object that has already been proven to be confined to a single thread, then that first object is confined to the same thread.

Ad Edit: In practice you can have an object that’s only accessed by a single thread at a time during its lifetime, but for which that single thread changes (a JDBC Connection object from a connection pool is a good example).

Proving that such an object is only ever accessed by a single thread is much harder than proving it for an object that’s confined to a single thread during its entire life, however.

And in my opinion those objects are never really “confined to a single thread” (which would imply a strong guarantee), but could be said to “be used by a single thread at a time only”.

More Related Contents:

  1. When and how should I use a ThreadLocal variable?
  2. Is iterating ConcurrentHashMap values thread safe?
  3. Are non-synchronised static methods thread safe if they don’t modify static class variables?
  4. How to wait for all threads to finish, using ExecutorService?
  5. Why must wait() always be in synchronized block
  6. What is the difference between Thread.start() and Thread.run()?
  7. Volatile vs Static in Java
  8. When would you call java’s thread.run() instead of thread.start()?
  9. Is a HashMap thread-safe for different keys?
  10. Why use a ReentrantLock if one can use synchronized(this)?
  11. Thread safe multitons in Java
  12. Is a volatile int in Java thread-safe?
  13. Java Executors: how can I set task priority?
  14. What are the main uses of yield(), and how does it differ from join() and interrupt()?
  15. Volatile variable in Java
  16. What is the JVM thread scheduling algorithm?
  17. How do I implement task prioritization using an ExecutorService in Java 5?
  18. How to stop a thread created by implementing runnable interface?
  19. Why does Thread.isInterrupted () always return false?
  20. When should I use a CompletionService over an ExecutorService?
  21. How does `this` reference to an outer class escape through publishing inner class instance?
  22. Java ExecutorService: awaitTermination of all recursively created tasks
  23. How do I prove programmatically that StringBuilder is not threadsafe?
  24. Which concurrent Queue implementation should I use in Java?
  25. Jboss Java EE container and an ExecutorService
  26. How to pause/resume all threads in an ExecutorService in Java?
  27. Multithreading Socket communication Client/Server
  28. How to get the Context from anywhere? [duplicate]
  29. Are 64 bit assignments in Java atomic on a 32 bit machine?
  30. Is LinkedList thread-safe when I’m accessing it with offer and poll exclusively?

Leave a Comment