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Are AtomicIntegers considered synchronization primitives, or is it just the methods provided by Java (wait(), notify(), etc).

I am confused about the definition of primitives, as atomicintegers can operate on int and provide lock free thread sage programming. Without the use of synchronized.

3rdeye7
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  • AtomicIntegers are not primitive. – DejaVuSansMono Nov 01 '16 at 17:52
  • Out of votes. Duplicate: [Definition of “synchronization primitive”](http://stackoverflow.com/questions/8017507/definition-of-synchronization-primitive) – Sotirios Delimanolis Nov 01 '16 at 17:53
  • @DejaVuSansMono I've read that and it wasn't that clear to me.Specifically, "The usually built using lower level mechanisms (e.g. atomic operations, memory barriers, spinlocks, context switches etc)." This is saying they can be built using atomic operations. – 3rdeye7 Nov 01 '16 at 18:00
  • @DejaVuSansMono Also, "Mutex, event, conditional variables and semaphores are all synchronization primitives". Please correct me if im wrong, arent semaphores, mutex, conditions, monitors, bounded buffers, etc just concepts. Like the model and concepts to follow when implementing thread-safe programming – 3rdeye7 Nov 01 '16 at 18:05

3 Answers3

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AtomicInteger is a class. Its methods are... well, methods. Neither one of those would be considered a synchronization primative.

The compareAndSet method, which is also used by incrementAndGet and other such methods, uses Unsafe.compareAndSwapInt (on OpenJDK 7, which is what I have handy). That's a native method — so it could well be considered a primitive. And in fact, on modern CPUs, it translates to a CAS instruction, so it's a primitive all the way down to the hardware level.

The class also relies on volatile's memory visibility, which is also a synchronization primitive.

yshavit
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  • In the case a random number generator, I've read through a lot of examples where most use atomic integers and seed without the use of synchronized. These are not actually using synchronization primitives, they would be using atomic primitives? – 3rdeye7 Nov 01 '16 at 18:09
  • "Synchronization" is itself an overloaded term. There's the keyword `synchronized` (with its associated semantics), and there's the concept of synchronizing one action after another -- which is a more abstract concept, and things like the `volatile` keyword give you that. For instance, JLS 17.4.4 talks about "synchronization order" in that latter sense. So even that followup question is a bit vague. – yshavit Nov 01 '16 at 19:49
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I think this question is a bit "vague"; but I think that "language primitive" typically refers to language elements that are part of the core of the language.

In other words: the keywords, and the associated semantics. In that sense; I would see the synchronized (in its two meanings) and volatile keywords as being the only "primitive" regarding multithreading.

Of course, classes such as Object; and therefore all its methods like wait(), notify() ... are also an essential part of Java (one which you can't avoid in the first place). And of course, same can be said about the Thread class.

Long story short: you can differentiate between concepts that exist as language keywords (and are thus handled by the compiler); and "on-top" concepts that come as "normal" classes. And as the answer from yshavit nicely describes, certain aspects of AtomicInteger can be directly mapped into the "native" side of things. So the real answer is maybe that, as said, the term "primitive" doesn't provide much aid in describing/differentiating concepts regarding Java multi-threading topics.

GhostCat
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Regarding your first query:

Are AtomicIntegers considered synchronization primitives, or is it just the methods provided by Java (wait(), notify(), etc).

No. AtomicInteger is neither a method nor synchronized primitive.

AtomicInteger is a class with methods. Have a look at oracle documentation page on atomic packages

A small toolkit of classes that support lock-free thread-safe programming on single variables. In essence, the classes in this package extend the notion of volatile values, fields, and array elements to those that also provide an atomic conditional update operation of the form:

boolean compareAndSet(expectedValue, updateValue);

The classes in this package also contain methods to get and unconditionally set values, as well as a weaker conditional atomic update operation weakCompareAndSet

Regarding your second query:

I am confused about the definition of primitives, as atomicintegers can operate on int and provide lock free thread sage programming. Without the use of synchronized.

One key note:

The scope of synchronized is broad in nature compared to AtomicInteger or AtomicXXX variables. With synchronized methods or blocks, you can protect critical section of code, whcih contains many statements.

The compareAndSet method is not a general replacement for locking. It applies only when critical updates for an object are confined to a single variable.

Atomic classes are not general purpose replacements for java.lang.Integer and related classes. However, AtomicInteger extends Number to allow uniform access by tools and utilities that deal with numerically-based classes.

Ravindra babu
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  • How about CountdownLatch, in java.util.conncurent? Are the synchronized primitives suggested in this article correct [link](http://stefan.kapferer.ch/2015/08/14/parallel-programming-summary1/#specific-synchronization-primitives)? – 3rdeye7 Nov 01 '16 at 20:21