Is javascript guaranteed to be single-threaded?

Javascript is known to be single-threaded in all modern browser implementations, but is that specified in any standard or is it just by tradition? Is it totally safe to assume that javascript is always single-threaded?

What is the most frequent concurrency issue you"ve encountered in Java?

This is a poll of sorts about common concurrency problems in Java. An example might be the classic deadlock or race condition or perhaps EDT threading bugs in Swing. I'm interested both in a breadth of possible issues but also in what issues are most common. So, please leave one specific answer of a Java concurrency bug per comment and vote up if you see one you've encountered.

can JavaScript flow of execution be interrupted?

I've always thought that, since JavaScript was single-threaded, I could attach event handlers without worrying about the handlers getting executed while I was in the middle of executing code. To my surprise, I found that they could. According to this answer, the 'Unresponsive Script' dialog box can cause events to be raised while the script is still running.

Why reading a volatile and writing to a field member is not scalable in Java?

Observe the following program written in Java (complete runnable version follows, but the important part of the program is in the snippet a little bit further below):

Is volatile expensive?

After reading http://gee.cs.oswego.edu/dl/jmm/cookbook.html about the implementation of volatile, especially section "Interactions with Atomic Instructions" I assume that reading a volatile variable without updating it needs a LoadLoad or a LoadStore barrier. Further down the page I see that LoadLoad and LoadStore are effectively no-ops on X86 CPUs. Does this mean that volatile read operations can be done without a explicit cache invalidation on x86, and is as fast a normal variable read (disregarding the reordering constraints of volatile)?

Ways to improve performance consistency

In the following example, one thread is sending "messages" via a ByteBuffer which is the consumer is taking. The best performance is very good but its not consistent.

java: concurrent collections

I'm trying to find one or more concurrent collections to use that I can implement the following behavior (the names are contrived for analogy purposes):

Is possible to postpone trigger fire in Quartz?

I have two processes:

Process 1 - implements runnable and can run forever. Process 2 - fires at fixed hour and minute of day (i've created a job that run with Quartz).