118 lines
5.0 KiB
Plaintext
118 lines
5.0 KiB
Plaintext
Copyright (c) 2002, 2022, Oracle and/or its affiliates. All rights reserved.
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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This code is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License version 2 only, as
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published by the Free Software Foundation.
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This code is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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version 2 for more details (a copy is included in the LICENSE file that
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accompanied this code).
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You should have received a copy of the GNU General Public License version
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2 along with this work; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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or visit www.oracle.com if you need additional information or have any
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questions.
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The Churn tests are a series of small programs designed to
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simply churn memory over, mixing in calls to GC and Finalization.
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They are all basically the same program with permutations.
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Each program contains:
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LocalRandom class -- used to isloate calls to random generator
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for reproducibility
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MemoryObject class -- simply allocated and reclaimed. contains
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a byte array
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Churn class -- entry point. Allocates threads and counts objects.
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When loop is done, sets Semaphore to signal threads to cease
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ThreadObject class -- allocates and deallocates (by assignment)
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MemoryObjects
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SemaphoreObject class -- static class for signalling threads when
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to stop running. Perhap poorly named.
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CommandLine class -- parses command line args. Static class.
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--------------------------
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Usage:
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java Churn [-l numberOfLoops] [-t numberOfThreads] [-a sizeOfArray] [-m multiplier] [-f <run forever>]
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NOTE: the options can be passed in any order
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numberOfLoops is the number of iterations a test will go through.
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This defaults to 2000
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numberOfThreads is the number of threads activating and deactivating
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MemoryObjects. This deaults to 2.
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sizeOfArray is the number of MemoryObjects each thread manipulates.
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This defaults to 1024.
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multiplier is a value used to determine how much memory each MemoryObject
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holds. It defaults to 10.
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The tests can be configured to run forever by passing -f on the
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command line. This is useful for continued stress testing outside
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of a test harness.
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-----------------------------
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The total amount of needed memory is approximately
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numberOfThreads * (sizeOfArray * sizeOfArray) * (multiplier / 2) bytes
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The default is about 10 Megs needed, not counting garbage collection
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overhead. Garbage collection doubles the memory requirements for
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programs that run out of heap space, so the true default size
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is 20 Megs.
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Testname What it does
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------------- ---------------------------------------------------------
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Churn1 Simply creates new MemObjects. No finalizers. No user
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calls to System.gc(). Count of objects simply grows
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since no method ever decreases the count -- object count
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equals total objects ever allocated. Memory used is
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approx = (object count) * (array size) * (multiplier) / 2
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Churn2 Same as Churn1, but adds a call to System.gc() every loop.
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Object Count should simply increase. About half the time,
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this test will hang before the 100th loop. About 10% of
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the time this test will SEG FAULT with either a BUS ERROR
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or ACCESS VIOLATION
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Churn3 Same as Churn1, but the MemoryObject class has a
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finalize() method on it. The method is empty. The objecty
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count should continue to rise. However, this program
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runs out of memory after around 35 loops. The threads
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dies from OutOfMemoryErrors. It looks as if the
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finalizers are not called fast enough during GC, so
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enough memory cannot be freed.
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Additionally, about 10% of the time, this program SEGFAULTS
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Churn3a Same as Churn3, but with an explicit call to
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System.runFinalization() in each loop.
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Occasionally, this test will run out of memory
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early on for one or more of the threads.
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Also, this test sometimes hangs, even if one or
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all of the ThreadObjects have died.
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Even if no threads die, and it doesn't hang, this
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program will still die with:
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java.lang.NullPointerException
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at java.lang.String.indexOf(String.java)
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at Churn3a.main(Churn3a.java:71)
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which contains only a call to join()
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Churn4 Same as Churn3, but with code in the finalize method
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which would decrement a *static* field in the class.
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This test runs out of memory much more quickly, something
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like after 3 or 4 loops.
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