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If multiple threads try to update the same member variable, it is called a race condition. But I was more interested in knowing how the JVM handles it internally if we don't handle it in our code by making it synchronised or something else? Will it hang my program? How will the JVM react to it? I thought the JVM would temporarily create a sync block for this situation, but I'm not sure what exactly would be happening.
If any of you have some insight, it would be good to know.
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Race conditions can be avoided by proper thread synchronization in critical sections. Thread synchronization can be achieved using a synchronized block of Java code. Thread synchronization can also be achieved using other synchronization constructs like locks or atomic variables like java. util.
To avoid race conditions, any operation on a shared resource – that is, on a resource that can be shared between threads – must be executed atomically. One way to achieve atomicity is by using critical sections — mutually exclusive parts of the program.
It can be eliminated by using no more than two levels of gating. An essential race condition occurs when an input has two transitions in less than the total feedback propagation time. Sometimes they are cured using inductive delay line elements to effectively increase the time duration of an input signal.
Another solution to avoid race condition is mutual exclusion. In mutual exclusion, if a thread is using a shared variable or thread, another thread will exclude itself from doing the same thing.
The precise term is a data race, which is a specialization of the general concept of a race condition. The term data race is an official, precisely specified concept, which means that it arises from a formal analysis of the code.
The only way to get the real picture is to go and study the Memory Model chapter of the Java Language Specification, but this is a simplified view: whenever you have a data race, there is almost no guarantee as to the outcome and a reading thread may see any value which has ever been written to the variable. Therein also lies the only guarantee: the thread will not observe an "out-of-thin-air" value, such which was never written. Well, unless you're dealing with longs or doubles, then you may see torn writes.
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