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Fixed the synchronization strategy in ExecutorServiceProvider #1470
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this seems to break a lot of tests |
Wow. Compiler bug? ASM bug? Both? |
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Could this failure be related to Guice 3.0 is incompatible with Java 8? See #393 |
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But the stacktrace there is really similar: |
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error message when tested with guice 4 |
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ConcurrentHashMap does not allow null as keys |
szarnekow
reviewed
May 5, 2020
| */ | ||
| @Singleton | ||
| public class ExecutorServiceProvider implements Provider<ExecutorService>, IDisposable { | ||
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| private final Map<String, ExecutorService> instanceCache = new ConcurrentHashMap<>(3); |
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Given that ConcurrentHashMap does not allow null-keys or null-values, it may also be ok to use Collections.synchronizedMap here, since I don't expect a lot of pressure on the lookup of an ExecutorService.
get(String key) should be rewritten to use computeIfAbsent(..).
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dispose must sync on the map, too.
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get(String key) should be rewritten to use
computeIfAbsent(..).
I can think of two ways; however, I am not convinced by either. In the first one, calling computeIfAbsent(...) inside the if (result == null) doesn't make much sense. We already know that the value is null before calling computeIfAbsent(...). The second one would block threads even if the map has a non-null value for the key requested by the second thread.
@szarnekow Please suggest if there is any other way to rewrite this method.
ExecutorService result = instanceCache.get(key);
if (result == null) {
synchronized (instanceCache) {
result = instanceCache.computeIfAbsent(key, k -> createInstance(k));
}
}
return result;
synchronized (instanceCache) {
return instanceCache.computeIfAbsent(key, k -> createInstance(k));
}
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Steps:
- Use a
Collections.synchronizedMap(new HashMap<>())for the field initializer - Rewrite and simplify get(String) towards
public ExecutorService get(String key) { return instanceCache.computeIfAbsent(key, this::createInstance)); } - fix dispose to sync on the instanceCache, too:
public void dipose() { synchronized(instanceCache) { .. } }
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@szarnekow computeIfAbsent(...) is not atomic. Don't we have to sync on the map?
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SynchronizedMap.computeIfAbsent(K, Function<? super K, ? extends V>) is safe.
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ok, tx for clarification.
Signed-off-by: nbhusare <[email protected]>
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Thank you, @nbhusare! |
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PS #1442 (comment) for details regarding this fix.
Signed-off-by: nbhusare [email protected]