[Bug] Memory Leak in getV8HeapStatistics() and getV8HeapSpaceStatistics()

[caoccao]

Problem

When V8 has been busy for a long while, calling getV8HeapStatistics() and getV8HeapSpaceStatistics() will experience memory leak or even crash JVM in a low chance.

Solution

Introduce sync and async modes.

Sync Mode

In sync mode, the context is purged immediately. This is the normal path without further change.

Async Mode

There are 1 global daemon thread and multiple probing threads.

Global Daemon Thread

1. Periodically peek a priority queue for expired context.
2. If the context is expired, request the context under the global lock.
3. If the context exists, purge the context.
4. If the context doesn't exist, do nothing.

Probing Thread

1. Register the resource under the global lock.
2. In the callback, request the context under the same global lock.
3. If the context is purged already, return immediately.
4. If the context is not purged, proceed to get the statistics and purge the context.