Build instructions

To start the HTTPS server:

./gradlew run

To start the HTTP server (no TLS):

./gradlew run --args="--no-tls"

Prerequisites

• JDK 11

Symptoms of CPU issue with HttpsServer

When connecting to the server with

curl -k https://localhost:8443/close

there is a response but one CPU gets used 100% until the server is shut down.

How to reproduce

After starting the server (see above), send an HTTP request with curl:

curl -k https://localhost:8443/open

This will trigger the handler that leaves the stream to which we write the request body open. This works fine, it does not cause one CPU to be used 100%.

But this will:

curl -k https://localhost:8443/close

This other handler processing the request does close the stream. This will yield an HTTP response but the server becomes unresponsive afterwards due to high CPU load.

Workaround

As helpfully suggested here, there's a workaround for this JDK bug:

applicationDefaultJvmArgs += [ "-Djdk.tls.acknowledgeCloseNotify=true" ]

Platforms where the bug occurs

• Arch Linux 5.1.7:
  • OpenJDK 12.0.1+12
  • OpenJDK 11.0.4+7
  • OpenJDK 11.0.3+4

What works

High CPU load does not occur when connecting to the HTTPS server using a browser (you'll have to accept the self-signed certificate first):

firefox https://localhost:8443/close

Also, using curl to connect to a regular HTTP server without TLS works fine:

./gradlew run --args="--no-tls"
curl http://localhost:8443/close

Findings from JDK Flight Recorder (JFR)

Directory with performance data gathered from JFR after calling curl -k https://localhost:8443/close.

Instructions to get JFR.

Threads Allocating

The thread performing the most allocation is likely 'HTTP-Dispatcher'. This is the most common allocation path for that class:

SSLEngineImpl.writeRecord(ByteBuffer[], int, int, ByteBuffer[], int, int) (50.2 %)
SSLEngineImpl.wrap(ByteBuffer[], int, int, ByteBuffer[], int, int)
SSLEngineImpl.wrap(ByteBuffer[], int, int, ByteBuffer)
SSLEngine.wrap(ByteBuffer, ByteBuffer)
SSLStreams$EngineWrapper.wrapAndSendX(ByteBuffer, boolean)
SSLStreams.doClosure()

Allocated Classes

The most allocated class is likely 'javax.net.ssl.SSLEngineResult'. This is the most common allocation path for that class:

SSLEngineImpl.writeRecord(ByteBuffer[], int, int, ByteBuffer[], int, int) (100 %)
SSLEngineImpl.wrap(ByteBuffer[], int, int, ByteBuffer[], int, int)
SSLEngineImpl.wrap(ByteBuffer[], int, int, ByteBuffer)
SSLEngine.wrap(ByteBuffer, ByteBuffer)
SSLStreams$EngineWrapper.wrapAndSendX(ByteBuffer, boolean)
SSLStreams.doClosure()