michael-o commented on a change in pull request #65:
URL: https://github.com/apache/maven-resolver/pull/65#discussion_r457649439
##########
File path:
maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/DefaultSyncContextFactory.java
##########
@@ -28,31 +30,59 @@
import org.eclipse.aether.artifact.Artifact;
import org.eclipse.aether.impl.SyncContextFactory;
import org.eclipse.aether.metadata.Metadata;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.inject.Singleton;
/**
- * A factory to create synchronization contexts. This default implementation
actually does not provide any real
- * synchronization but merely completes the repository system.
+ * A factory to create synchronization contexts. This default implementation
uses fair global locking
+ * based on {@link ReentrantReadWriteLock}. Explicit artifacts and metadata
passed are ignored.
*/
@Named
+@Singleton
public class DefaultSyncContextFactory
implements SyncContextFactory
{
+ private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(
true );
public SyncContext newInstance( RepositorySystemSession session, boolean
shared )
{
- return new DefaultSyncContext();
+ return new DefaultSyncContext( shared ? lock.readLock() :
lock.writeLock(), shared );
}
static class DefaultSyncContext
implements SyncContext
{
+ private static final Logger LOGGER = LoggerFactory.getLogger(
DefaultSyncContext.class );
+
+ private final Lock lock;
+ private final boolean shared;
+ private int lockHoldCount;
+
+ DefaultSyncContext( Lock lock, boolean shared )
+ {
+ this.lock = lock;
+ this.shared = shared;
+ }
public void acquire( Collection<? extends Artifact> artifact,
Collection<? extends Metadata> metadata )
{
+ LOGGER.trace( "Acquiring global {} lock (currently held: {})",
+ shared ? "read" : "write", lockHoldCount );
+ lock.lock();
Review comment:
> We are downloading and writing a file. Writing a stream on the disk
must be treated by the write lock because it is exclusive lock
Correct.
> Where is the read lock used and why?
Please look into the code. I am not the caller, but the callee only.
> I guess this issue is about locking the writes to the disk from one JVM
but two or more threads.
Correct also.
> Additionally, the fairness must not be taken as any functionality. No
logic must rely on any fairness.
I take this as a fair point. This can be addressed in a separate
issue/release, but should not make any difference in regard of locking, but
order only.
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