1 Copyright (c) 2002, 2018, Oracle and/or its affiliates. All rights reserved. 2 DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 4 This code is free software; you can redistribute it and/or modify it 5 under the terms of the GNU General Public License version 2 only, as 6 published by the Free Software Foundation. 7 8 This code is distributed in the hope that it will be useful, but WITHOUT 9 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 10 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 11 version 2 for more details (a copy is included in the LICENSE file that 12 accompanied this code). 13 14 You should have received a copy of the GNU General Public License version 15 2 along with this work; if not, write to the Free Software Foundation, 16 Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 17 18 Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 19 or visit www.oracle.com if you need additional information or have any 20 questions. 21 22 The Churn tests are a series of small programs designed to 23 simply churn memory over, mixing in calls to GC and Finalization. 24 They are all basically the same program with permutations. 25 Each program contains: 26 27 LocalRandom class -- used to isloate calls to random generator 28 for reproducibility 29 30 MemoryObject class -- simply allocated and reclaimed. contains 31 a byte array 32 33 Churn class -- entry point. Allocates threads and counts objects. 34 When loop is done, sets Semaphore to signal threads to cease 35 36 ThreadObject class -- allocates and deallocates (by assignment) 37 MemoryObjects 38 39 SemaphoreObject class -- static class for signalling threads when 40 to stop running. Perhap poorly named. 41 42 CommandLine class -- parses command line args. Static class. 43 -------------------------- 44 Usage: 45 46 java Churn [-l numberOfLoops] [-t numberOfThreads] [-a sizeOfArray] [-m multiplier] [-f <run forever>] [-s seed] 47 48 NOTE: the options can be passed in any order 49 50 51 seed is the seed for the LocalRandom pseudo-random generator 52 53 numberOfLoops is the number of iterations a test will go through. 54 This defaults to 2000 55 56 numberOfThreads is the number of threads activating and deactivating 57 MemoryObjects. This deaults to 2. 58 59 sizeOfArray is the number of MemoryObjects each thread manipulates. 60 This defaults to 1024. 61 62 multiplier is a value used to determine how much memory each MemoryObject 63 holds. It defaults to 10. 64 65 The tests can be configured to run forever by passing -f on the 66 command line. This is useful for continued stress testing outside 67 of a test harness. 68 ----------------------------- 69 The total amount of needed memory is approximately 70 numberOfThreads * (sizeOfArray * sizeOfArray) * (multiplier / 2) bytes 71 72 The default is about 10 Megs needed, not couting garbage collection 73 overhead. Garbage collection doubles the memory requirements for 74 programs that run out of heap space, so the the true default size 75 is 20 Megs. 76 77 78 Testname What it does 79 ------------- --------------------------------------------------------- 80 Churn1 Simply creates new MemObjects. No finalizers. No user 81 calls to System.gc(). Count of objects simply grows 82 since no method ever decreases the count -- object count 83 equals total objects ever allocated. Memory used is 84 approx = (object count) * (array size) * (multiplier) / 2 85 86 Churn2 Same as Churn1, but adds a call to System.gc() every loop. 87 Object Count should simply increase. About half the time, 88 this test will hang before the 100th loop. About 10% of 89 the time this test will SEG FAULT with either a BUS ERROR 90 or ACCESS VIOLATION 91 92 Churn3 Same as Churn1, but the MemoryObject class has a 93 finalize() method on it. The method is empty. The objecty 94 count should continue to rise. However, this program 95 runs out of memory after around 35 loops. The threads 96 dies from OutOfMemoryErrors. It looks as if the 97 finalizers are not called fast enough during GC, so 98 enough memory cannot be freed. 99 Additionally, about 10% of the time, this program SEGFAULTS 100 101 Churn3a Same as Churn3, but with an explicit call to 102 System.runFinalization() in each loop. 103 Occasionally, this test will run out of memory 104 early on for one or more of the threads. 105 Also, this test sometimes hangs, even if one or 106 all of the ThreadObjects have died. 107 Even if no threads die, and it doesn't hang, this 108 program will still die with: 109 java.lang.NullPointerException 110 at java.lang.String.indexOf(String.java) 111 at Churn3a.main(Churn3a.java:71) 112 which contains only a call to join() 113 114 115 116 Churn4 Same as Churn3, but with code in the finalize method 117 which would decrement a *static* field in the class. 118 This test runs out of memory much more quickly, something 119 like after 3 or 4 loops.