Last active
September 21, 2019 00:06
-
-
Save juanmf/87f71cfc3c7c00471eafcf318485e314 to your computer and use it in GitHub Desktop.
context switching tests.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import lombok.AllArgsConstructor; | |
import org.junit.Test; | |
import java.util.concurrent.CompletableFuture; | |
import java.util.concurrent.ExecutionException; | |
import java.util.concurrent.Executor; | |
import java.util.concurrent.ForkJoinPool; | |
import java.util.concurrent.TimeUnit; | |
import java.util.concurrent.atomic.AtomicBoolean; | |
import java.util.concurrent.atomic.AtomicLong; | |
public class ParallelismTest { | |
private static final int MAX_ROUNDS = 1000; | |
private static final int ROUND_SIZE = 100000; | |
@Test | |
public void trySameThreadTest() throws ClassNotFoundException, ExecutionException, InterruptedException { | |
// runs all in main thread, sequentially | |
CompletableFuture f = CompletableFuture.runAsync(() -> sleep(1, 0)); | |
f.thenRun(() -> System.out.println(Thread.currentThread().getName())); | |
f.get(); | |
} | |
@Test | |
public void trySequentialTest() throws ClassNotFoundException, ExecutionException, InterruptedException { | |
// runs all in main thread, sequentially | |
Executor pool = command -> command.run(); | |
tryIncrease(pool, false); | |
} | |
@Test | |
public void trySequentialSwitchingThreadTest() throws ClassNotFoundException, ExecutionException, InterruptedException { | |
// Tries to ensure a fast voluntary context switch (access a resource) | |
ForkJoinPool pool = new ForkJoinPool(1); | |
tryIncrease(pool, true); | |
} | |
@Test | |
public void tryConcurrentTest() throws ClassNotFoundException, ExecutionException, InterruptedException { | |
// Tries to ensure a fast voluntary context switch (access a resource) | |
ForkJoinPool pool = ForkJoinPool.commonPool(); | |
tryIncrease(pool, true); | |
} | |
/** | |
* Interesting results: | |
* Using long acum ({@see LongContainer}) correctness is only warrantied by {@see trySequentialTest} | |
* Atomic is necessary for {@see trySequentialSwitchingThreadTest} too. As even synchronizing different threads to run sequentially | |
* can increase (++) on stale values due to bad timing on thread suspension. | |
* | |
* When test is too long (~4 seconds to run) {@see trySequentialTest} behaves similar to {@see trySequentialSwitchingThreadTest} due | |
* to involuntary context switch. | |
* | |
* threadNames updated status is seldom visible from main thread, when updated from worker thread. | |
* | |
* @param pool | |
* @param runConcurrentThreads | |
* @throws ClassNotFoundException | |
* @throws ExecutionException | |
* @throws InterruptedException | |
*/ | |
public void tryIncrease(Executor pool, boolean runConcurrentThreads) throws ClassNotFoundException, ExecutionException, InterruptedException { | |
long startTimeNano = System.nanoTime(); | |
StringBuffer threadNames = new StringBuffer(); | |
AtomicLong acum = new AtomicLong(0L); | |
runRounds(acum, pool, threadNames); | |
if (runConcurrentThreads) { | |
// We didn't wait for each task, wait for the pool then. | |
((ForkJoinPool) pool).awaitQuiescence(1, TimeUnit.DAYS); | |
} | |
System.out.println(threadNames.toString()); | |
System.out.println(String.format("With pool %s \n => Took: %,d nanos \n accum: %,d, \n ", | |
pool, | |
(System.nanoTime() - startTimeNano), | |
acum.get())); | |
} | |
private void runRounds(AtomicLong accum, Executor pool, final StringBuffer threadNames) | |
throws ExecutionException, InterruptedException { | |
final AtomicBoolean is1stRound = new AtomicBoolean(true); | |
for (int round = 0; round < MAX_ROUNDS; round ++) { | |
pool.execute(() -> increase(accum, threadNames, is1stRound.get())); | |
is1stRound.compareAndSet(true, false); | |
} | |
} | |
private void increase(AtomicLong accum, final StringBuffer threadNames, boolean dumpName) { | |
if (dumpName) { | |
threadNames.append(Thread.currentThread().getName()); | |
threadNames.append("\n"); | |
} | |
for (int i = 0; i < ROUND_SIZE; i++) { | |
sleep(0L, 0); | |
accum.incrementAndGet(); | |
} | |
} | |
private void sleep (long millis, int nanos) { | |
if (millis <= 0L || (millis <= 0L && nanos <= 0)) { | |
return; | |
} | |
try { | |
Thread.sleep(millis, nanos); | |
} catch (InterruptedException e) { | |
e.printStackTrace(); | |
} | |
} | |
@AllArgsConstructor(staticName = "of") | |
private static class LongContainer { | |
long theLong; | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment