How to prevent hangs on SocketInputStream.socketRead0 in Java?
You should consider a Non-blocking HTTP client like Grizzly or Netty which do not have blocking operations to hang a thread.
As Clint said, you should consider a Non-blocking HTTP client, or (seeing that you are using the Apache Httpclient) implement a Multithreaded request execution to prevent possible hangs of the main application thread (this not solve the problem but is better than restart your app because is freezed). Anyway, you set the setStaleConnectionCheckEnabled property but the stale connection check is not 100% reliable, from the Apache Httpclient tutorial:
One of the major shortcomings of the classic blocking I/O model is that the network socket can react to I/O events only when blocked in an I/O operation. When a connection is released back to the manager, it can be kept alive however it is unable to monitor the status of the socket and react to any I/O events. If the connection gets closed on the server side, the client side connection is unable to detect the change in the connection state (and react appropriately by closing the socket on its end).
HttpClient tries to mitigate the problem by testing whether the connection is 'stale', that is no longer valid because it was closed on the server side, prior to using the connection for executing an HTTP request. The stale connection check is not 100% reliable and adds 10 to 30 ms overhead to each request execution.
The Apache HttpComponents crew recommends the implementation of a Connection eviction policy
The only feasible solution that does not involve a one thread per socket model for idle connections is a dedicated monitor thread used to evict connections that are considered expired due to a long period of inactivity. The monitor thread can periodically call ClientConnectionManager#closeExpiredConnections() method to close all expired connections and evict closed connections from the pool. It can also optionally call ClientConnectionManager#closeIdleConnections() method to close all connections that have been idle over a given period of time.
Take a look at the sample code of the Connection eviction policy section and try to implement it in your application along with the Multithread request execution, I think the implementation of both mechanisms will prevent your undesired hangs.
Though this question mentions Windows, I have the same problem on Linux. It appears there is a flaw in the way the JVM implements blocking socket timeouts:
- https://bugs.openjdk.java.net/browse/JDK-8049846
- https://bugs.openjdk.java.net/browse/JDK-8075484
To summarize, timeout for blocking sockets is implemented by calling poll on Linux (and select on Windows) to determine that data is available before calling recv. However, at least on Linux, both methods can spuriously indicate that data is available when it is not, leading to recv blocking indefinitely.
From poll(2) man page BUGS section:
See the discussion of spurious readiness notifications under the BUGS section of select(2).
From select(2) man page BUGS section:
Under Linux, select() may report a socket file descriptor as "ready for reading", while nevertheless a subsequent read blocks. This could for example happen when data has arrived but upon examination has wrong checksum and is discarded. There may be other circumstances in which a file descriptor is spuriously reported as ready. Thus it may be safer to use O_NONBLOCK on sockets that should not block.
The Apache HTTP Client code is a bit hard to follow, but it appears that connection expiration is only set for HTTP keep-alive connections (which you've disabled) and is indefinite unless the server specifies otherwise. Therefore, as pointed out by oleg, the Connection eviction policy approach won't work in your case and can't be relied upon in general.
I have more than 50 machines that make about 200k requests/day/machine. They are running Amazon Linux AMI 2017.03. I previously had jdk1.8.0_102, now I have jdk1.8.0_131. I am using both apacheHttpClient and OKHttp as scraping libraries.
Each machine was running 50 threads, and sometimes, the threads get lost. After profiling with Youkit java profiler I got
ScraperThread42 State: RUNNABLE CPU usage on sample: 0ms
java.net.SocketInputStream.socketRead0(FileDescriptor, byte[], int, int, int) SocketInputStream.java (native)
java.net.SocketInputStream.socketRead(FileDescriptor, byte[], int, int, int) SocketInputStream.java:116
java.net.SocketInputStream.read(byte[], int, int, int) SocketInputStream.java:171
java.net.SocketInputStream.read(byte[], int, int) SocketInputStream.java:141
okio.Okio$2.read(Buffer, long) Okio.java:139
okio.AsyncTimeout$2.read(Buffer, long) AsyncTimeout.java:211
okio.RealBufferedSource.indexOf(byte, long) RealBufferedSource.java:306
okio.RealBufferedSource.indexOf(byte) RealBufferedSource.java:300
okio.RealBufferedSource.readUtf8LineStrict() RealBufferedSource.java:196
okhttp3.internal.http1.Http1Codec.readResponse() Http1Codec.java:191
okhttp3.internal.connection.RealConnection.createTunnel(int, int, Request, HttpUrl) RealConnection.java:303
okhttp3.internal.connection.RealConnection.buildTunneledConnection(int, int, int, ConnectionSpecSelector) RealConnection.java:156
okhttp3.internal.connection.RealConnection.connect(int, int, int, List, boolean) RealConnection.java:112
okhttp3.internal.connection.StreamAllocation.findConnection(int, int, int, boolean) StreamAllocation.java:193
okhttp3.internal.connection.StreamAllocation.findHealthyConnection(int, int, int, boolean, boolean) StreamAllocation.java:129
okhttp3.internal.connection.StreamAllocation.newStream(OkHttpClient, boolean) StreamAllocation.java:98
okhttp3.internal.connection.ConnectInterceptor.intercept(Interceptor$Chain) ConnectInterceptor.java:42
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RealInterceptorChain.proceed(Request) RealInterceptorChain.java:67
okhttp3.internal.http.BridgeInterceptor.intercept(Interceptor$Chain) BridgeInterceptor.java:93
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(Interceptor$Chain) RetryAndFollowUpInterceptor.java:124
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RealInterceptorChain.proceed(Request) RealInterceptorChain.java:67
okhttp3.RealCall.getResponseWithInterceptorChain() RealCall.java:198
okhttp3.RealCall.execute() RealCall.java:83
I found out that they have a fix for this
https://bugs.openjdk.java.net/browse/JDK-8172578
in JDK 8u152 (early access). I have installed it on one of our machines. Now I am waiting to see some good results.