[Bug] Race Condition in V8Guard

[caoccao]

Problem

There is a global thread-safe priority queue for V8Guard instances. There are flaws in the current implementation.

1. There is no synchronization between take() and add() in the daemon thread.
2. The daemon thread doesn't check whether a V8Guard instance is closed or not.

That creates a slight chance of adding a closed V8Guard in the daemon thread when there is constant heavy load. That results in executions terminated early.

Impact Versions

v3.1.3-v3.1.6

Solution

• Add synchronized check against V8Guard.isClosed().