Time Warp
Virtual Time for the JVM

This library lets you create virtual-time clocks and install them as the JVM's clock to help with testing.

A virtual-time Clock will modify the operation of System.currentTimeMillis(), System.nanoTime(), Thread.sleep, Object.wait(long), LockSupport.parkNanos and any other operation relying on timeouts.

Use this library to slow-down/speed-up/manually control the JVM's clock to make your timing-sensitive tests less flaky.

Status

Early days. We've begun using TimeWarp's ScaledClock (and SystemClock) in Quasar tests. ManualClock hasn't been tested, so it probably doesn't work yet.

Usage

1. Clone and build the repository with ./gradlew or use Maven artifact co.paralleluniverse:timewarp:0.1.0-SNAPSHOT from the Sonatype snapshot repository (https://oss.sonatype.org/content/repositories/snapshots)

2. Add the JAR file to your bootstrap classpath with -Xbootclasspath/a:[timewarp jar] and as an agent with -javaagent:[timewarp jar]

3. Install one of the provided clocks, SystemClock, ScaledClock, or ManualClock, using the VirtualClock class. Please consult the Javadocs for detailed information. Alternatively, you can pass an integer as a command-line argument to the agent (e.g. -javaagent:[timewarp jar]=3), which would install a global scaling clock, that would slow down the system clock by a factor equal to the parameter. So an argument of 3 would install a ScaledClock with a scaling factor of 0.33333.

License

MIT

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