Akka Actor中的Httpclient死锁

Question

I have an actor which receive message,and download file by httpclient.
code sample:

@Override
public void onReceive(Object message) throws Exception {
    HttpClient client = new DefaultHttpClient();
    ...
    httpGet.releaseConnection()
    ...
}

Problems occurred after a few days.
From log,it shows actor block at httpclient request.
Block is ok,but it seems httpclient deadlock,actor don't process any message further.
How is that happens?

log:

Sending message to DownloadActor  
...DownloadActor Receive message  
BasicClientConnectionManager:159 - Get connection for route  
...  

BasicClientConnectionManager:201 - Releasing connection  
Sending message to DownloadActor  
...DownloadActor Receive message  
BasicClientConnectionManager:159 - Get connection for route  

Sending message to DownloadActor  
Sending message to DownloadActor  
Sending message to DownloadActor  
Sending message to DownloadActor  
Sending message to DownloadActor  

thread dump:

"grabSystem-akka.actor.default-dispatcher-67" prio=10 tid=0x00007fa4d4004800 nid=0x2ad8 waiting on condition [0x00007fa5671a7000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000411a2a010> (a akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinPool)
        at scala.concurrent.forkjoin.ForkJoinPool.scan(ForkJoinPool.java:2075)
        at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
        at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

"grabSystem-akka.actor.default-dispatcher-66" prio=10 tid=0x00007fa4b4001000 nid=0x5ea runnable [0x00007fa5679ae000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.read(SocketInputStream.java:152)
        at java.net.SocketInputStream.read(SocketInputStream.java:122)
        at org.apache.http.impl.io.AbstractSessionInputBuffer.read(AbstractSessionInputBuffer.java:204)
        at org.apache.http.impl.conn.LoggingSessionInputBuffer.read(LoggingSessionInputBuffer.java:82)
        at org.apache.http.impl.io.ChunkedInputStream.read(ChunkedInputStream.java:177)
        at org.apache.http.conn.EofSensorInputStream.read(EofSensorInputStream.java:138)
        at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:283)
        at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:325)
        at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:177)
        - locked <0x0000000412038e10> (a java.io.InputStreamReader)
        at java.io.InputStreamReader.read(InputStreamReader.java:184)
        at java.io.Reader.read(Reader.java:140)
        at org.apache.http.util.EntityUtils.toString(EntityUtils.java:233)
        at org.apache.http.util.EntityUtils.toString(EntityUtils.java:273)
        at com.baidu.grab.core.DownloadActor.onReceive(DownloadActor.java:102)
        at akka.actor.UntypedActor$$anonfun$receive$1.applyOrElse(UntypedActor.scala:167)
        at akka.actor.Actor$class.aroundReceive(Actor.scala:465)
        at akka.actor.UntypedActor.aroundReceive(UntypedActor.scala:97)
        at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516)
        at akka.actor.ActorCell.invoke(ActorCell.scala:487)
        at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:238)
        at akka.dispatch.Mailbox.run(Mailbox.scala:220)
        at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:393)
        at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
        at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
        at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
        at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

Answer 1

If I understand your question, this might help explain what is going on. An actor processes messages from its mailbox serially. It the HttpClient is blocking, then the actor will not complete processing that message, and will process no further message until the block is cleared and the message processing can be completed.

If you wanted to have the actor not block, then wrap the call the HttpClient activity in a future or send the work off to a pool of actors to handle the situation while you continue to process.