Ensure thread safety of AllOfPromise

[pivovarit]

What was changed

Replaced the internal AllOfPromise int notReadyCount counter with a thread-safe final AtomicInteger

Why?

AllOfPromise registers multiple Promise instances that were created outside of its scope and uses the handle() method to schedule counter decrements. When the counter reaches zero, it means that all futures completed.

However, handle() method can be executed by different threads, and the internal counter in the current form:

• doesn't guarantee that new value will be immediately visible for other threads due to the lack of volatile
• doesn't guarantee atomicity of the increment/decrement operations, which can result in lost updates

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[Quinn-With-Two-Ns]

@pivovarit all threads in a workflow are managed and coordinated by the SDK, no external threads not managed by the SDK are allowed to be created inside a workflow, so no two threads are ever running concurrently so this should not be necessary .

[pivovarit]

Does it mean that those subsequent handle() callbacks are effectively executed serially by the same thread?

[Quinn-With-Two-Ns]

They are executed serially, potentially by different threads, all with all threads using a common lock for serialization