Issue
An HTTPS API is used for stress testing. The response time (RT) gradually increases during the stress testing process. The transactions per second (TPS) and success rate drop to zero or have a tendency to drop to zero.
The following error message appears in the sampling log:
java.net.SocketException: Socket closed
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:668)
at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:542)
at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:414)
at org.apache.jmeter.protocol.http.sampler.LazySchemeSocketFactory.connectSocket(LazySchemeSocketFactory.java:97)
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
at org.apache.jmeter.protocol.http.sampler.hc.ManagedClientConnectionImpl.open(ManagedClientConnectionImpl.java:318)
at org.apache.jmeter.protocol.http.sampler.MeasuringConnectionManager$MeasuredConnection.open(MeasuringConnectionManager.java:114)
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445)
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.executeRequest(HTTPHC4Impl.java:695)
at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:454)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:74)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1189)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1178)
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:498)
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:424)
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:255)
at java.lang.Thread.run(Thread.java:766)
The Timing Waterfall of the sampling log shows that all the time is spent during the connection establishment phase.
Cause
In most cases, the java.net.SocketException: Socket closed error occurs because no connection timeout period is configured.
Solution
If you select Use KeepAlive on the Basic tab of the HTTP request sampler, we recommend that you configure the following parameters on the Advanced tab:
Set the Implementation parameter to HttpClient4.
Set the Connect parameter to a value from 10 to 60 seconds as the idle connection timeout period. This prevents the connection from being disconnected due to the failure to receive the Keep-Alive header returned by the stress testing server.

For more information, see JMeterSocketClosed.