On Fri, 13 Jan 2023 19:09:54 GMT, Archie L. Cobbs <d...@openjdk.org> wrote:
>> This PR adds a new lint warning category `this-escape`. >> >> It also adds `@SuppressWarnings` annotations as needed to the JDK itself to >> allow the JDK to continue to compile with `-Xlint:all`. >> >> A 'this' escape warning is generated for a constructor `A()` in a class `A` >> when the compiler detects that the following situation is _in theory >> possible:_ >> * Some subclass `B extends A` exists, and `B` is defined in a separate >> source file (i.e., compilation unit) >> * Some constructor `B()` of `B` invokes `A()` as its superclass constructor >> * During the execution of `A()`, some non-static method of `B.foo()` could >> get invoked, perhaps indirectly >> >> In the above scenario, `B.foo()` would execute before `A()` has returned and >> before `B()` has performed any initialization. To the extent `B.foo()` >> accesses any fields of `B` - all of which are still uninitialized - it is >> likely to function incorrectly. >> >> Note, when determining if a 'this' escape is possible, the compiler makes no >> assumptions about code outside of the current compilation unit. It doesn't >> look outside of the current source file to see what might actually happen >> when a method is invoked. It does follow method and constructors within the >> current compilation unit, and applies a simplified >> union-of-all-possible-branches data flow analysis to see where 'this' could >> end up. >> >> From my review, virtually all of the warnings generated in the various JDK >> modules are valid warnings in the sense that a 'this' escape, as defined >> above, is really and truly possible. However, that doesn't imply that any >> bugs were found within the JDK - only that the possibility of a certain type >> of bug exists if certain superclass constructors are used by someone, >> somewhere, someday. >> >> For several "popular" classes, this PR also adds `@implNote`'s to the >> offending constructors so that subclass implementors are made aware of the >> threat. For one example, `TreeMap(Map)` invokes `putAll()` and `put()`. >> >> More details and a couple of motivating examples are given in an included >> [doc >> file](https://github.com/archiecobbs/jdk/blob/ThisEscape/src/java.base/share/classes/java/lang/doc-files/ThisEscape.html) >> that these `@implNote`'s link to. See also the recent thread on `amber-dev` >> for some background. >> >> Ideally, over time the owners of the various modules would review their >> `@SuppressWarnings("this-escape")` annotations and determine which other >> constructors also warranted such an `@implNote`. >> >> Because of all the`@SuppressWarnings` annotations, this PR touches a bunch >> of different JDK modules. My apologies for that. Adding these annotations >> was determined to be the more conservative approach, as compared to just >> excepting `this-escape` from various module builds globally. >> >> **Patch Navigation Guide** >> >> * Non-trivial compiler changes: >> * `src/jdk.compiler/share/classes/com/sun/tools/javac/code/Lint.java` >> * `src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java` >> * `src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java` >> * `src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeInfo.java` >> * >> `src/jdk.compiler/share/classes/com/sun/tools/javac/comp/ThisEscapeAnalyzer.java` >> * >> `src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties` >> * >> `src/jdk.compiler/share/classes/com/sun/tools/javac/resources/javac.properties` >> >> * Javadoc additions of `@implNote`: >> >> * `src/java.base/share/classes/java/io/PipedReader.java` >> * `src/java.base/share/classes/java/io/PipedWriter.java` >> * `src/java.base/share/classes/java/lang/Throwable.java` >> * `src/java.base/share/classes/java/util/ArrayDeque.java` >> * `src/java.base/share/classes/java/util/EnumMap.java` >> * `src/java.base/share/classes/java/util/HashSet.java` >> * `src/java.base/share/classes/java/util/Hashtable.java` >> * `src/java.base/share/classes/java/util/LinkedList.java` >> * `src/java.base/share/classes/java/util/TreeMap.java` >> * `src/java.base/share/classes/java/util/TreeSet.java` >> >> * New unit tests >> * `test/langtools/tools/javac/warnings/ThisEscape/*.java` >> >> * **Everything else** is just adding `@SuppressWarnings("this-escape")` > > Archie L. Cobbs has updated the pull request incrementally with three > additional commits since the last revision: > > - Use more idiomatic test for java.lang.Object. > - Revert 27cb30129; the error was actually fixed in edf3c3f51. > - Fix formatting issue with the "this-escape" --help-lint description. src/jdk.compiler/share/classes/com/sun/tools/javac/comp/ThisEscapeAnalyzer.java line 1088: > 1086: private <T extends JCTree> void visitLooped(T tree, Consumer<T> > visitor) { > 1087: visitScoped(tree, false, t -> { > 1088: while (true) { I have also been thinking if the loop analysis could go wild and execute a large, unbound number of times. But it seems from Archie's experiments that this probably won't occur in "normal" code and worst case scenario if that were to occur we can always limit the number of times we will process loops to a set number of times ------------- PR: https://git.openjdk.org/jdk/pull/11874
