org.scalatest.concurrent.Conductors
The current value of the thread clock.
The current value of the thread clock.
the current beat value
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
The maximum amount of time allowed between successive beats is configured by the timeout
field of
the PatienceConfig
passed implicitly as the last parameter.
The interval to sleep between successive checks for progress is configured by the value contained in the passed
interval
parameter.
the Interval
configuration parameter
the PatienceConfig
object containing the (used) timeout
and
(unused) interval
parameters
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
The maximum amount of time allowed between successive beats is configured by the value contained in the passed
timeout
parameter.
The interval to sleep between successive checks for progress is configured by by the interval
field of
the PatienceConfig
passed implicitly as the last parameter.
the Timeout
configuration parameter
the PatienceConfig
object containing the (unused) timeout
and
(used) interval
parameters
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
The maximum amount of time allowed between successive beats is configured by the value contained in the passed
timeout
parameter.
The interval to sleep between successive checks for progress is configured by the value contained in the passed
interval
parameter.
the Timeout
configuration parameter
the Interval
configuration parameter
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
Conducts a multi-threaded test using the configured maximum allowed time between beats
(the timeout
) and the configured time to sleep between checks (the interval
).
the PatienceConfig
object containing the timeout
and
interval
parameters used to configure the multi-threaded test
Indicates whether either of the two overloaded conduct
methods
have been invoked.
Indicates whether either of the two overloaded conduct
methods
have been invoked.
This method returns true if either conduct
method has been invoked. The
conduct
method may have returned or not. (In other words, a true
result from this method does not mean the conduct
method has returned,
just that it was already been invoked and,therefore, the multi-threaded scenario it
conducts has definitely begun.)
Indicates whether the conductor has been frozen.
Indicates whether the conductor has been frozen.
Note: The only way a thread
can freeze the conductor is by calling withConductorFrozen
.
Creates a new thread that will execute the specified function.
Creates a new thread that will execute the specified function.
The name of the thread will be of the form Conductor-Thread-N, where N is some integer.
This method may be safely called by any thread.
the function to be executed by the newly created thread
the newly created thread
Creates a new thread with the specified name that will execute the specified function.
Creates a new thread with the specified name that will execute the specified function.
This method may be safely called by any thread.
the name of the newly created thread
the function to be executed by the newly created thread
the newly created thread
Blocks the current thread until the thread beat reaches the specified value, at which point the current thread will be unblocked.
Blocks the current thread until the thread beat reaches the specified value, at which point the current thread will be unblocked.
the tick value to wait for
if the a beat
less than or equal to zero is passed
Invokes conduct
and after conduct
method returns,
if conduct
returns normally (i.e., without throwing
an exception), invokes the passed function.
Invokes conduct
and after conduct
method returns,
if conduct
returns normally (i.e., without throwing
an exception), invokes the passed function.
If conduct
completes abruptly with an exception, this method
will complete abruptly with the same exception and not execute the passed
function.
This method must be called by the thread that instantiated this Conductor
,
and that same thread will invoke conduct
and, if it returns noramlly, execute
the passed function.
Because whenFinished
invokes conduct
, it can only be invoked
once on a Conductor
instance. As a result, if you need to pass a block of
code to whenFinished
it should be the last statement of your test. If you
don't have a block of code that needs to be run once all the threads have finished
successfully, then you can simply invoke conduct
and never invoke
whenFinished
.
the function to execute after conduct
call returns
if the calling thread is not the thread that
instantiated this Conductor
, or if conduct
has already
been invoked on this conductor.
Executes the passed function with the Conductor
frozen so that it
won't advance the clock.
Executes the passed function with the Conductor
frozen so that it
won't advance the clock.
While the Conductor
is frozen, the beat will not advance. Once the
passed function has completed executing, the Conductor
will be unfrozen
so that the beat will advance when all threads are blocked, as normal.
the function to execute while the Conductor
is frozen.
The overloaded thread method that takes a String name has been deprecated and will be removed in a future version of ScalaTest. Please use threadNamed instead.
The overloaded thread method that takes a String name has been deprecated and will be removed in a future version of ScalaTest. Please use threadNamed instead.
The overloaded thread method that takes a String name has been deprecated and will be removed in a future version of ScalaTest. Please use threadNamed instead.
Class that facilitates the testing of classes, traits, and libraries designed to be used by multiple threads concurrently.
A
Conductor
conducts a multi-threaded scenario by maintaining a clock of "beats." Beats are numbered starting with 0. You can ask aConductor
to run threads that interact with the class, trait, or library (the subject) you want to test. A thread can call theConductor
'swaitForBeat
method, which will cause the thread to block until that beat has been reached. TheConductor
will advance the beat only when all threads participating in the test are blocked. By tying the timing of thread activities to specific beats, you can write tests for concurrent systems that have deterministic interleavings of threads.A
Conductor
object has a three-phase lifecycle. It begins its life in the setup phase. During this phase, you can start threads by invoking thethread
method on theConductor
. Whenconduct
is invoked on aConductor
, it enters the conducting phase. During this phase it conducts the one multi-threaded scenario it was designed to conduct. After all participating threads have exited, either by returning normally or throwing an exception, theconduct
method will complete, either by returning normally or throwing an exception. As soon as theconduct
method completes, theConductor
enters its defunct phase. Once theConductor
has conducted a multi-threaded scenario, it is defunct and can't be reused. To run the same test again, you'll need to create a new instance ofConductor
.Here's an example of the use of
Conductor
to test theArrayBlockingQueue
class fromjava.util.concurrent
:When the test shown is run, it will create one thread named producer and another named consumer. The producer thread will eventually execute the code passed as a by-name parameter to
thread("producer")
:Similarly, the consumer thread will eventually execute the code passed as a by-name parameter to
thread("consumer")
:The
thread
calls create the threads and starts them, but they will not immediately execute the by-name parameter passed to them. They will first block, waiting for theConductor
to give them a green light to proceed.The next call in the test is
whenFinished
. This method will first callconduct
on theConductor
, which will wait until all threads that were created (in this case, producer and consumer) are at the "starting line", i.e., they have all started and are blocked, waiting on the green light. Theconduct
method will then give these threads the green light and they will all start executing their blocks concurrently.When the threads are given the green light, the beat is 0. The first thing the producer thread does is put 42 in into the queue. As the queue is empty at this point, this succeeds. The producer thread next attempts to put a 17 into the queue, but because the queue has size 1, this can't succeed until the consumer thread has read the 42 from the queue. This hasn't happened yet, so producer blocks. Meanwhile, the consumer thread's first act is to call
waitForBeat(1)
. Because the beat starts out at 0, this call will block the consumer thread. As a result, once the producer thread has executedbuf put 17
and the consumer thread has executedwaitForBeat(1)
, both threads will be blocked.The
Conductor
maintains a clock that wakes up periodically and checks to see if all threads participating in the multi-threaded scenario (in this case, producer and consumer) are blocked. If so, it increments the beat. Thus sometime later the beat will be incremented, from 0 to 1. Because consumer was waiting for beat 1, it will wake up (i.e., thewaitForBeat(1)
call will return) and execute the next line of code in its block,buf.take should be (42)
. This will succeed, because the producer thread had previously (during beat 0) put 42 into the queue. This act will also make producer runnable again, because it was blocked on the secondput
, which was waiting for another thread to read that 42.Now both threads are unblocked and able to execute their next statement. The order is non-deterministic, and can even be simultaneous if running on multiple cores. If the
consumer
thread happens to executebuf.take should be (17)
first, it will block (buf.take
will not return), because the queue is at that point empty. At some point later, the producer thread will executebuf put 17
, which will unblock the consumer thread. Again both threads will be runnable and the order non-deterministic and possibly simulataneous. The producer thread may charge ahead and run its next statement,beat should be (1)
. This will succeed because the beat is indeed 1 at this point. As this is the last statement in the producer's block, the producer thread will exit normally (it won't throw an exception). At some point later the consumer thread will be allowed to complete its last statement, thebuf.take
call will return 17. The consumer thread will execute17 should be (17)
. This will succeed and as this was the last statement in its block, the consumer will return normally.If either the producer or consumer thread had completed abruptbly with an exception, the
conduct
method (which was called bywhenFinished
) would have completed abruptly with an exception to indicate the test failed. However, since both threads returned normally,conduct
will return. Becauseconduct
doesn't throw an exception,whenFinished
will execute the block of code passed as a by-name parameter to it:buf should be ('empty)
. This will succeed, because the queue is indeed empty at this point. ThewhenFinished
method will then return, and because thewhenFinished
call was the last statement in the test and it didn't throw an exception, the test completes successfully.This test tests
ArrayBlockingQueue
, to make sure it works as expected. If there were a bug inArrayBlockingQueue
such as aput
called on a full queue didn't block, but instead overwrote the previous value, this test would detect it. However, if there were a bug inArrayBlockingQueue
such that a call totake
called on an empty queue never blocked and always returned 0, this test might not detect it. The reason is that whether the consumer thread will ever calltake
on an empty queue during this test is non-deterministic. It depends on how the threads get scheduled during beat 1. What is deterministic in this test, because the consumer thread blocks during beat 0, is that the producer thread will definitely attempt to write to a full queue. To make sure the other scenario is tested, you'd need a different test:In this test, the producer thread will block, waiting for beat 1. The consumer thread will invoke
buf.take
as its first act. This will block, because the queue is empty. Because both threads are blocked, theConductor
will at some point later increment the beat to 1. This will awaken the producer thread. It will return from itswaitForBeat(1)
call and executebuf put 42
. This will unblock the consumer thread, which will take the 42, and so on.The problem that
Conductor
is designed to address is the difficulty, caused by the non-deterministic nature of thread scheduling, of testing classes, traits, and libraries that are intended to be used by multiple threads. If you just create a test in which one thread reads from anArrayBlockingQueue
and another writes to it, you can't be sure that you have tested all possible interleavings of threads, no matter how many times you run the test. The purpose ofConductor
is to enable you to write tests with deterministic interleavings of threads. If you write one test for each possible interleaving of threads, then you can be sure you have all the scenarios tested. The two tests shown here, for example, ensure that both the scenario in which a producer thread tries to write to a full queue and the scenario in which a consumer thread tries to take from an empty queue are tested.Class
Conductor
was inspired by the MultithreadedTC project, created by Bill Pugh and Nat Ayewah of the University of Maryland.Although useful, bear in mind that a
Conductor
's results are not guaranteed to be accurate 100% of the time. The reason is that it usesjava.lang.Thread
'sgetState
method to decide when to advance the beat. This use goes against the advice given in the Javadoc documentation forgetState
, which says, "This method is designed for use in monitoring of the system state, not for synchronization." In short, sometimes the return value ofgetState
occasionally may be inacurrate, which in turn means that sometimes aConductor
could decide to advance the beat too early. In practice,Conductor
has proven to be very helpful when developing thread safe classes. It is also useful in for regression tests, but you may have to tolerate occasional false negatives.