dosubot[bot] commented on issue #2634:
URL:
https://github.com/apache/incubator-hugegraph/issues/2634#issuecomment-2287774251
<!-- Answer -->
The `waitGraphLock` method in the `PartitionCache` class ensures that a
thread waits until the lock for a specific graph is released before proceeding.
This method contributes to thread safety by preventing concurrent modifications
to the graph's data structures while another thread is performing operations on
them.
Here is the relevant code snippet:
```java
public void waitGraphLock(String graphName) {
var lock = getOrCreateGraphLock(graphName);
while (lock.get()) {
Thread.onSpinWait();
}
}
```
The method works by checking the state of an `AtomicBoolean` lock associated
with the graph. If the lock is set (i.e., `true`), the thread will spin-wait
until the lock is released (i.e., set to `false`). This ensures that no other
thread can proceed with operations on the graph until the current operation is
complete.
Although `waitGraphLock` does not hold the lock during subsequent
operations, it ensures that the thread only proceeds when it is safe to do so,
thus maintaining thread safety. The actual locking and unlocking are handled by
the `lockGraph` and `unlockGraph` methods, respectively, which set and reset
the `AtomicBoolean` lock.
Here is how `lockGraph` and `unlockGraph` work:
```java
public void lockGraph(String graphName) {
var lock = getOrCreateGraphLock(graphName);
while (!lock.compareAndSet(false, true)) {
Thread.onSpinWait();
}
}
public void unlockGraph(String graphName) {
var lock = getOrCreateGraphLock(graphName);
lock.set(false);
}
```
In summary, `waitGraphLock` ensures that a thread waits for the lock to be
released before proceeding, thereby contributing to thread safety by preventing
concurrent modifications
<sup>[[1]](https://github.com/apache/incubator-hugegraph/blob/master/hugegraph-pd/hg-pd-common/src/main/java/org/apache/hugegraph/pd/common/PartitionCache.java)</sup>.
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