如果我的程序中有多个线程，从技术上讲每个线程是否都有自己的堆栈？ 每个线程都有自己的堆吗？

Question

I have been trying to find the answer to this question in the API (and with Google) but I am not able to find anything that directly discusses the state of the call stack and heap in a multi-threaded program.

Also, does a synchronised object get flip flopped between both stacks (assuming they are seperate stacks)

Answer 1

They share the heap, but each thread has its own stack (otherwise it wouldn't know what it's executing).

Nothing is flip flopped (I don't understand why you think that would happen). Objects can't be synchronized, only code is synchronized (by acquiring an object's monitor or lock).

Answer 2

Multiple threads in Java share the same heap space. Each thread gets its own stack.

The Java Virtual Machine is stacked based. In pseudocode an add instruction may look like this.

push 2 //Stack: 2
push 3 //Stack: 2,3
add    //Stack: 5

If threads shared the same address space then it may turn into something weird since they share the same stack. When they start popping off values from other threads the virtual machine will do strange things and may crash.

Here is what it might look like if we did that same example above on two threads.(This is just a possible way the stack might look like.)

Thread 1               Thread 2
push 2 //Stack: 2    : push 2 //Stack: 2,2
push 3 //Stack: 2,2,3: push 3 //Stack: 2,2,3,3
add //Stack 2,2,6    : add //Stack 2,8

You can easily see that if they shared the same stack, things would get corrupt fast.