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feature: [loom] replace the usages of synchronized with ReentrantLock #6971

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lightClouds917 opened this issue Nov 1, 2024 · 0 comments · May be fixed by #6983
Open

feature: [loom] replace the usages of synchronized with ReentrantLock #6971

lightClouds917 opened this issue Nov 1, 2024 · 0 comments · May be fixed by #6983
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@lightClouds917
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Why you need it?

Is your feature request related to a problem? Please describe in details
To use virtual threads in JDK 21, we need to remove the usage of synchronized to prevent the issue where "a virtual thread cannot be unmounted during blocking operations because it is pinned to its carrier.

Details

There are two scenarios in which a virtual thread cannot be unmounted during blocking operations because it is pinned to its carrier:

When it executes code inside a synchronized block or method, or
When it executes a native method or a foreign function.
Pinning does not make an application incorrect, but it might hinder its scalability. If a virtual thread performs a blocking operation such as I/O or BlockingQueue.take() while it is pinned, then its carrier and the underlying OS thread are blocked for the duration of the operation. Frequent pinning for long durations can harm the scalability of an application by capturing carriers.

The scheduler does not compensate for pinning by expanding its parallelism. Instead, avoid frequent and long-lived pinning by revising synchronized blocks or methods that run frequently and guard potentially long I/O operations to use java.util.concurrent.locks.ReentrantLock instead. There is no need to replace synchronized blocks and methods that are used infrequently (e.g., only performed at startup) or that guard in-memory operations. As always, strive to keep locking policies simple and clear.

https://openjdk.org/jeps/444
https://openjdk.org/projects/loom/

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A clear and concise description of what you want to happen. You can explain more about input of the feature, and output of it.

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