Copyright (c) 2002, 2020, Oracle and/or its affiliates. All rights reserved. DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. This code is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 only, as published by the Free Software Foundation. This code is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License version 2 for more details (a copy is included in the LICENSE file that accompanied this code). You should have received a copy of the GNU General Public License version 2 along with this work; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA or visit www.oracle.com if you need additional information or have any questions. The Churn tests are a series of small programs designed to simply churn memory over, mixing in calls to GC and Finalization. They are all basically the same program with permutations. Each program contains: LocalRandom class -- used to isloate calls to random generator for reproducibility MemoryObject class -- simply allocated and reclaimed. contains a byte array Churn class -- entry point. Allocates threads and counts objects. When loop is done, sets Semaphore to signal threads to cease ThreadObject class -- allocates and deallocates (by assignment) MemoryObjects SemaphoreObject class -- static class for signalling threads when to stop running. Perhap poorly named. CommandLine class -- parses command line args. Static class. -------------------------- Usage: java Churn [-l numberOfLoops] [-t numberOfThreads] [-a sizeOfArray] [-m multiplier] [-f ] NOTE: the options can be passed in any order numberOfLoops is the number of iterations a test will go through. This defaults to 2000 numberOfThreads is the number of threads activating and deactivating MemoryObjects. This deaults to 2. sizeOfArray is the number of MemoryObjects each thread manipulates. This defaults to 1024. multiplier is a value used to determine how much memory each MemoryObject holds. It defaults to 10. The tests can be configured to run forever by passing -f on the command line. This is useful for continued stress testing outside of a test harness. ----------------------------- The total amount of needed memory is approximately numberOfThreads * (sizeOfArray * sizeOfArray) * (multiplier / 2) bytes The default is about 10 Megs needed, not couting garbage collection overhead. Garbage collection doubles the memory requirements for programs that run out of heap space, so the the true default size is 20 Megs. Testname What it does ------------- --------------------------------------------------------- Churn1 Simply creates new MemObjects. No finalizers. No user calls to System.gc(). Count of objects simply grows since no method ever decreases the count -- object count equals total objects ever allocated. Memory used is approx = (object count) * (array size) * (multiplier) / 2 Churn2 Same as Churn1, but adds a call to System.gc() every loop. Object Count should simply increase. About half the time, this test will hang before the 100th loop. About 10% of the time this test will SEG FAULT with either a BUS ERROR or ACCESS VIOLATION Churn3 Same as Churn1, but the MemoryObject class has a finalize() method on it. The method is empty. The objecty count should continue to rise. However, this program runs out of memory after around 35 loops. The threads dies from OutOfMemoryErrors. It looks as if the finalizers are not called fast enough during GC, so enough memory cannot be freed. Additionally, about 10% of the time, this program SEGFAULTS Churn3a Same as Churn3, but with an explicit call to System.runFinalization() in each loop. Occasionally, this test will run out of memory early on for one or more of the threads. Also, this test sometimes hangs, even if one or all of the ThreadObjects have died. Even if no threads die, and it doesn't hang, this program will still die with: java.lang.NullPointerException at java.lang.String.indexOf(String.java) at Churn3a.main(Churn3a.java:71) which contains only a call to join() Churn4 Same as Churn3, but with code in the finalize method which would decrement a *static* field in the class. This test runs out of memory much more quickly, something like after 3 or 4 loops.