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21
22
23 ABOUT
24
25 Once published, it is impossible to add methods to an interface without
26 breaking existing implementations (specifically, adding a method to an
27 interface is not a source-compatible change). The longer the time since a
28 library has been published, the more likely it is that this restriction will
29 cause grief for its maintainers.
30
31 The addition of closures to the Java language in JDK 8 place additional stress
32 on the aging Collection interfaces; one of the most significant benefits of
33 closures is that it enables the development of more powerful libraries. It
34 would be disappointing to add a language feature that enables better libraries
35 while at the same time not extending the core libraries to take advantage of
36 that feature.
37
38 A mechanism for adding new methods to existing interfaces is proposed, which is
39 called virtual extension (or default) methods. Existing interfaces can be
40 augmented without compromising backward compatibility by adding extension
41 methods to the interface, whose declaration would contain instructions for
42 finding the default implementation in the event that implementers do not
43 provide a method body. A key characteristic of extension methods is that they
44 are virtual methods just like other interface methods, but provide a default
45 implementation in the event that the implementing class does not provide a
46 method body.
47
48 VM support is necessary to implement virtual extension methods.
49
50
51 OVERVIEW
52
53 The test suite is organized in the following manner.
54
55 The tests rely on a framework to generate class hierarchies and tests
56 directly in bytecode from a pseudo-code in Java. Pseudo-code is written
57 using builder pattern and fluent coding style.
58
59 The framework is located in src/vm/runtime/defmeth/shared and divided into
60 /data and /builder sections.
61
62 As an example, the following code:
63
64 TestBuilder b = factory.getBuilder();
65
66 Interface I = b.intf("I")
67 .defaultMethod("m", "()I").returns(1).build()
68 .build();
69
70 ConcreteClass C = b.clazz("C").implement(I)
71 .concreteMethod("m", "()I").returns(2).build()
72 .build();
73
74 b.test().callSite(I, C, "m", "()I").returns(2).done()
75 .test().callSite(C, C, "m", "()I").returns(2).done()
76
77 .run();
78
79 translates into bytecode equivalent of:
80
81 2-class hierarchy:
82
83 interface I {
84 int m() default { return 1; }
85 }
86
87 class C implements I {
88 public int m() { return 2; }
89 }
90
91 and 2 tests:
92
93 Test1_I_C_m {
94 static void test() {
95 I i = new C();
96 if (i.m() != 2) throw new TestFailure();
97 }
98 }
99
100 Test2_C_C_m {
101 static void test() {
102 C c = new C();
103 if (c.m() != 2) throw new TestFailure();
104 }
105 }
106
107 TestBuilder.run() calls Test1_I_C_m.test() and Test2_C_C_m.test() and
108 performs failure reporting, if necessary.
109
110 All tests are located in src/vm/runtime/defmeth and are grouped according
111 to the area they excercise. The test groups are:
112 - AccessibilityFlagsTest
113 - BasicTest
114 - ConflictingDefaultsTest
115 - DefaultVsAbstractTest
116 - MethodResolutionTest
117 - ObjectMethodOverridesTest
118 - PrivateMethodsTest
119 - RedefineTest
120 - StaticMethodsTest
121 - StressTest
122 - SuperCallTest
123
124 Each test group can be executed in different modes. For each mode there's a
125 corresponding scenario in src/vm/runtime/defmeth/scenarios.
126
127 Scenarios are organized in the following manner:
128
129 .../scenarios/[test_group]_[majorVer]_[methodFlags]_[invocationType]_[shouldRedefine]
130
131 where
132
133 majorVer - major version of class files for generated concrete classes
134 values: ver49, ver52
135
136 methodFlags - additional access flags for methods in generated classes
137 values:
138 none == no additional flags
139 sync == ACC_SYNCHRONIZED
140 strict == ACC_STRICT
141 syncstrict == ACC_SYNCHRONIZED | ACC_STRICT
142
143 invocationType - how methods in test hiearchies are invoked during testing
144 values:
145 direct - using invoke* bytecodes
146 reflect - using Reflection API
147 invoke - using invokedynamic & java.lang.invoke API (MethodHandles/JSR292)
148
149 redefine - whether to preload and redefine classes before running individual tests
150 values: redefine, noredefine
151
152 testGroup - name of test group being used
153 values: BasicTests/BridgeMethod/etc
154
155
156 STRESS TESTING
157
158 Stress test differs from other scenarios - it has only 2 modes: redefine and noredefine.
159
160 Stress scenario is the following:
161 - in multiple threads (5 by default)...
162 - ... continuously run random vm.runtime.defmeth.* tests ...
163 - ... in random configurations ...
164 - ... until predefined period of time is over...
165 - ... or any failures occured.
166
167
168 HOW TO RUN
169
170 Directly from command-line:
171
172 $ java -cp ${VMTESTBASE}/bin/classes vm.runtime.defmeth.shared.DefMethTest
173
174 Specify testing mode:
175 -flags <int>
176 additional access flags on default methods (default: 0)
177
178 -ver <int>
179 class file major version (default: 52)
180
181 -redefine <boolean>
182 redefine classes during execution (default: false)
183
184 -mode [direct|reflect|invoke]
185 specify method invocation mechanism (default: direct):
186 - direct - invoke* instructions in bytecode
187 - reflect - Reflection API
188 - invoke - invokedynamic & MethodHandle.invoke*
189
190 -execMode [DIRECT|REFLECTION|INVOKE_EXACT|INVOKE_GENERIC|INVOKE_WITH_ARGS|INDY]
191 specify concrete execution mode
192
193 Execution-specific flags:
194 -list <boolean>
195 list available tests
196
197 -filter <regex>
198 filter tests by name
199 (default: .* )
200
201 If you run tests directly from command line, in order to make "-redefine true",
202 StressTest or RedefineTest work, additional steps are necessary:
203 add -agentlib:redefineClasses to JVM options
204 set correct LD_LIBRARY_PATH:
205 LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:${VM_TESTBASE}/bin/lib/${PLATFORM}/vm/runtime/defmeth/shared/
206
207 Also, it is possible to run any test group directly:
208
209 $ java -cp ${VMTESTBASE}/bin/classes vm.runtime.defmeth.BasicTest
210
211 StressTest has some specific options:
212 -stressTime <long>
213 Stress execution time in seconds (default: 60)
214
215 -stressThreadsFactor <int>
216 Stress threads factor (default: 1)
217
218 -seed <int>
219 force deterministic behavior (default: 0)
220
221 -redefine <boolean>
222 use scenarios w/ class redefinition (default: false)
223
224 -ver <int>
225 minimum class file version to be used in the tests (default: 49)
226
227 -ignoreTestFailures
228 ignore failures of individual tests
229
230 To simplify failure analysis, the framework has some additional flags to produce
231 diagnostics output:
232
233 -Dvm.runtime.defmeth.printTests
234 print pseudo-code for each test;
235
236 -Dvm.runtime.defmeth.printAssembly
237 print bytecode assembly for all generated class files;
238
239 -Dvm.runtime.defmeth.printASMify
240 print "asmified" version of generated class files;
241 very useful when preparing reduced test cases.
242
243 -Dvm.runtime.defmeth.dumpClasses
244 dump class files under DUMP_CLASS_FILES in <test_name> folder
245
246 -Dvm.runtime.defmeth.printStackTrace
247 print full stack traces for all errors and test failures
248
249 -Dvm.runtime.defmeth.traceClassRedefinition
250 trace class redefinition during testing
251
252 LINKS
253
254 [1] "Design and Implementation of Default Methods in Hotspot JVM", by Keith McGuigan, 09/18/2012
255 http://cr.openjdk.java.net/~kamg/default_methods_in_hotspot.txt
256
257 [2] "Featherweight Defenders: A formal model for virtual extension methods in Java", by Brian Goetz, Robert Field, 03/27/2012
258 http://cr.openjdk.java.net/~briangoetz/lambda/featherweight-defenders.pdf
259
260 [3] "Interface evolution via virtual extension methods", by Brian Goetz, 4th draft, 06/2011
261 http://cr.openjdk.java.net/~briangoetz/lambda/Defender%20Methods%20v4.pdf