arne-bdt commented on issue #2787:
URL: https://github.com/apache/jena/issues/2787#issuecomment-2431661976
In an attempt to make the possible blockage and cause visible to the user, I
may have inadvertently fixed it:
```java
private static volatile boolean initialized = false ;
private static Semaphore initializationSemaphore = new Semaphore(1);
private static ThreadLocal<Boolean> isInitializing =
ThreadLocal.withInitial(() -> false);
public static void init() {
// Once jena is initialized, all calls are an immediate return.
if ( initialized )
return ;
// if the same thread is calling init(), while the initialization is in
progress, return immediately
if(isInitializing.get())
return ;
isInitializing.set(true); // set the flag to true to indicate that the
initialization is in progress
try {
// Only one thread can initialize Jena.
if(initializationSemaphore.tryAcquire(5, TimeUnit.SECONDS)) {
if ( initialized )
return ;
setup();
if ( DEBUG_INIT )
singleton.debug(DEBUG_INIT);
singleton.initialize();
singleton.debug(false);
// Last so overlapping initialization waits on the synchronized
initialized = true;
}
} catch (InterruptedException e) {
throw new RuntimeException("Timeout while waiting for semaphore to
initialize JenaSystem. Please call JenaSystem.init() before working with
multiple threads.", e);
} finally {
initializationSemaphore.release();
isInitializing.remove();
}
}
```
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