is it possible to define execution order for a set of threads in java

Question

My understanding is that threads in theory are executed in parallel. JVM decides; when a resource is available which thread to pick from the waiting thread queue (based on some

Answer 1

You cannot tell the thread scheduler which order to execute threads in. If you need to ensure that a certain piece of code which is running on thread A must run before another piece of code running on thread B, you must enforce that order using locks or wait()/notify().

For example, you could use a variable which was accessible to both threads as a "flag" to indicate whether it is safe for thread B to go ahead. Thread B could wait() in a loop, checking the value of that variable. Then when it was safe for thread B to run, thread A could set the variable and wake thread B up using notify().

So yes, it is possible to enforce a desired order between things which happen on different threads. Generally, though, you want to avoid writing such low-level, detailed code. It is just too easy to get things wrong and cause subtle, hard-to-find bugs. When you are dealing with multithreaded code, always try to use high-level building blocks if you can.