123 lines
6.9 KiB
Plaintext
123 lines
6.9 KiB
Plaintext
Copyright (c) 2014, 2021, 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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Here are tests that were developed for "G1 support for long running applications" feature. In effect,
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here is only one test with a lot of configurations.
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Feature description:
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G1 used to unload classes only during full collections. Goal of feature is to unload unused classes
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without resorting to full gc.
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What does test checks:
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- that unreferenced classloader will be collected without full gc. This is checked with WhiteBox.is
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ClassAlive method.
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- that referenced classloader will live. This is checked with WhiteBox.isClassAlive method as well.
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Also it is checked that classloader will be finalized and enqueued to queue of phantom references.
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In what aspects/circumstances checks performed:
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- classloaders that we expect to be collected can be comlpetely unreferenced, referenced with phant
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om reference and with weak reference. Test can check that presence of phantom/weak reference doesn't
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keep classloader alive.
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Test has flag "-referenceMode" that has valid options:
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"phantom" for phantom reference,
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"weak" for weak reference and
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"none" for not keeping reference at all.
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- to avoid class unloading we can keep reference to classloader itself, class or object.
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This behavior can be adjusted with flag "-keep" that has valid options:
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"classloader",
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"class" and
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"object".
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- according to test plan several ways of classloading are covered.
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This behavior is adjusted with "classloadingMethod" flag that has valid options
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"plain",
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"reflection",
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"jni",
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"hidden_classloader".
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- classloaders that we expect to live can be referenced in several ways.
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This behavior can be adjusted with flag "-keepRefMode" that has valid options:
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"strong_reference" for starighforward keeping strong reference,
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"static_field" for keeping reference in static field of alive class,
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"stack_local" for keeping reference in local variable of running thread,
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"thread_field" for keeping reference in field of running thread's object,
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"thread_itself" if we want object to be a running thread itself,
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"static_field_of_root_class". In this case reference will be kept in static field of class that wa
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s loaded by null classloader.
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"jni_global_ref". In this case global reference will be kept in native library.
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"jni_local_ref", In this case local reference will be kept in JNI call in running thread.
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- Another aspect is that class can be humongous.
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Humongous classes can be enabled with "-humongousClass" command line option. Valid options are
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"true" and "false".
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- Another aspect that is covered with tests is that class methods can be compiled by JIT compiler.
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This behavior can be adjusted with "-compilationLevel" and "-compilationNumber" options. First
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one has self-explaining name, latter sets number of optimization/deoptimozation of each class.
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- Next aspect is class redefinition.
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You can enable classes redefinition with "-redefineClasses" flag. Valid options are "true" and
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"false".
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Test implementation details:
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Test supposed to be ran with G1 gc and -XX:+ExplicitGCProvokesConcurrent option. In the end of exec
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ution test checks if full gc happened. If this is the case the test throws descriptive exception and
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fails.
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Test guts design:
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Test in loop performs the following until time is over (timelimit is set up with "-stressTime" opti
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on):
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- loads class that gonna live or gonna be unloaded. Decision depends upon Random.nextBoolean().
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- previous action produces collection of Assertions (what assertion is is explained a little bit lat
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er). Assertions are saved into AssertionContainer.
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- takes from AssertionContainer assertions that are already mature for check and performs checks. "M
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ature" means that required number of System.gc() calls happened since assertion was created.
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What "Assertion" is:
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Assertion incapsulates check that concrete class will be alive or dead. Hazard is that we can't perf
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orm check just after we removed last reference to classloader. We have to wait some number of concurr
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ent-mark-cycles, i.e. System.gc() calls. For this reason we put each assertion in AssertionContainer
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and get back much later, when it's ready for check.
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Classes of assertions form the following simple hierarchy:
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gc.g1.unloading.check.Assertion
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|| || ||
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\/ || \/
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gc.g1.unloading.check.FinalizedAssertion || gc.g1.unloading.check.PhantomizedAssertion
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\/
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gc.g1.unloading.check.ClassAssertion
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FinalizedAssertion checks that unreferenced classloader will be finalized.
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PhantomizedAssertion checks that phantom reference to classloader will be enqueued to ReferenceQueue.
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ClassAssertion checks that class will be dead or alive using WhiteBox.isClassAlive method.
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Other implemention notes:
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There are some other auxiliary threads, but they are not crucial for understanding the logic.
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There are a lot of configurations of the same test in testlist. All configurations use the same mai
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n method as entry point, but impose different test flags. Configurations are autogenerated with "gene
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rate.sh" script.
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Other test options:
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-DFailTestIfNothingChecked=true. (vm flag) Set this if you want test to fail if nothing was checked
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and test appeared to be useless. It can happen, for example, in slow modes that force compilation.
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-numberOfChecksLimit. (test flag) Set this number if you want test to pass after certain number of c
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hecks performed. (Not to waste time.) To some extent this turns stress test into functional test.
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-numberOfGCsBeforeCheck. (test flag) This option sets number of System.gc() calls that have to be do
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ne before each assertion will be ready to perform checks.
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-inMemoryCompilation. (test flag) This option defines the way of classes creation. If this is true t
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hen classes are compiled with javac API. If false - classes are produced by rewriting classname in "g
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olden" bytecode.
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