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()
RuntimeMXBean.getStartTime()
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.
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.
Fork note: refactor and rename the fixed epcoh clock to offset clock and made some refactor. Manual and scaled clock where not much tested then. Offset clock works fine and has been used on large application simulation and benchmarks.
-
Clone and build the repository with
./gradlew
or use Maven artifactco.paralleluniverse:timewarp:0.1.0-SNAPSHOT
from the Sonatype snapshot repository (https://oss.sonatype.org/content/repositories/snapshots
) -
Add the JAR file to your bootstrap classpath with
-Xbootclasspath/a:[timewarp jar]
and as an agent with-javaagent:[timewarp jar]
-
Install one of the provided clocks,
SystemClock
,OffsetClock
,ScaledClock
, orManualClock
. This can be done either:- By code using the
VirtualClock
class. Please consult the Javadocs for detailed information. - By configuration, using agent command-line argument:
-javaagent:[timewarp jar]=[clock conf]
. See below for more information.
- By code using the
This clock apply a constant offset to the system clock. This offset can be defined either by:
- the number of milliseconds to add :
-javaagent:[timewarp jar]=offset=[millis]
- with an absolute date, the offset is calculated at the JVM start as the difference between the date and the JVM start date :
-javaagent:[timewarp jar]=offset=@[ISO date]
- a state file. The state file is a text file that contains the absolute date, like the previous option. The state file is periodically written with a date a
few minute ahead in the future to ensure that in case ensure that in case of JVM carsh or restart the next JVM execution won't see time that overlaps previous
execution.
Usage :
-javaagent:[timewarp jar]=offset=#[state file path]
Since these clock has no impact on time relative function, you can use the method name filter in order to wrap only the needed methods :
-javaagent:[timewarp jar]=includesMethods=System_currentTimeMillis:RuntimeMXBean_getStartTime,offset=...
Examples:
- one day past in time :
-javaagent:[timewarp jar]=includesMethods=System_currentTimeMillis:RuntimeMXBean_getStartTime,offset=-86400000
- simulate a JVM start at 2016-08-30 18:45:00 :
-javaagent:[timewarp jar]=includesMethods=System_currentTimeMillis:RuntimeMXBean_getStartTime,offset=@20160830T184500
- use a state file in
~/.faketime
:-javaagent:[timewarp jar]=includesMethods=System_currentTimeMillis:RuntimeMXBean_getStartTime,offset=#~/.faketime
** initialize the file~/.faketime
with the initial date, e.g.20160830T184500
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