What operations in Java are considered atomic?

java multithreading atomicity
robinmag picture robinmag · Jan 21, 2011 · Viewed 27.4k times · Source

What operations in Java are considered atomic?

Answer

maaartinus picture maaartinus · Jan 21, 2011
  • all assignments of primitive types except for long and double
  • all assignments of references
  • all assignments of volatile variables
  • all operations of java.concurrent.Atomic* classes

and maybe something more. Look at the jls.

As noted in the comments, atomicity does not imply visibility. So while another thread is guaranteed not to see a partially written int, it may never see the new value.

The operations on long and double are on common 64 bit CPUs atomic as well, although there's no guarantee. See also this feature request.

Related questions

Atomic Operations and multithreading

Recently I was reading a tutorial, in that I came across a statement that says.. "The Java language specification guarantees that reading or writing a variable is an atomic operation(unless the variable is of type long or double). Operations …

Read More
When is AtomicInteger preferrable over synchronized?

Since AtomicInteger can be at at least an order of magnitude slower than an int protected by synchronized, why would I ever want to use AtomicInteger? For example, if all I want is to increment an int value in a …

Read More
Difference between wait() and sleep()

What is the difference between a wait() and sleep() in Threads? Is my understanding that a wait()-ing Thread is still in running mode and uses CPU cycles but a sleep()-ing does not consume any CPU cycles correct? Why …

Read More