On Fri, 9 Jun 2023 15:47:54 GMT, Jaikiran Pai <j...@openjdk.org> wrote:
>> Can I please get a review of this change which proposes to fix the issue >> noted in https://bugs.openjdk.org/browse/JDK-8308184? >> >> When an application is launched, the `app` classloader internally uses a >> `jdk.internal.loader.URLClassPath` to find and load the main class being >> launched. The `URLClassPath` uses a list of classpath entries to find >> resources. Depending on the classpath entry, the `URLClassPath` will use a >> relevant loader. A couple of such loaders are `URLClassPath$FileLoader` (for >> loading resources from directories) and `URLClassPath$JarLoader` (for >> loading resources from jar files). >> >> `JarLoader` creates instances of `java.net.URL` to represent the jar file >> being loaded. `java.net.URL` uses protocol specific >> `java.net.URLStreamHandler` instance to handle connections to those URLs. >> When constructing an instance of `URL`, callers can pass a protocol handler. >> If it is not passed then the `URL` class looks for protocol handlers that >> might have been configured by the application. The >> `java.protocol.handler.pkgs` system property is the one which allows >> overriding the protocol handlers (even for the `jar` protocol). When this >> property is set, the `URL` class triggers lookup and classloading of the >> protocol handler classes. >> >> The issue that is reported is triggered when the >> `java.protocol.handler.pkgs` system property is set and the classpath has >> too many jar files. `app` classloader triggers lookup of the main class and >> the `URLClassPath` picks up the first entry in the classpath and uses a >> `JarLoader` (in this example our classpath entries have a jar file at the >> beginning of the list). The `JarLoader` instantiates a `java.net.URL`, which >> notices that the `java.protocol.handler.pkgs` is set, so it now triggers >> lookup of a (different) class using the same classloader and thus the same >> `URLClassPath`. The `URLClassPath` picks the next classpath entry and then >> calls into the `URL` again through the `JarLoader`. This sequence ends up >> being re-entrant calls and given the large number of classpath entries, >> these re-entrant calls end up with a `StackOverflowError` as shown in the >> linked JBS issue. >> >> The commit in this PR fixes this issue by using the system provided protocol >> handler implementation of the `jar` protocol in the `app` classloader. This >> results in the `URL` instances created through the `JarLoader` to use this >> specific handler instance. This allows the `app` classloader which is >> responsible for loading the application's main class ... > > Jaikiran Pai has updated the pull request incrementally with one additional > commit since the last revision: > > newline at end of test file Using the built-in jar protocol handler looks right. I like Alan's suggestion to use the fully qualified name in the source to make it clearer. test/jdk/java/net/URL/HandlersPkgPrefix/LargeClasspathWithPkgPrefix.java line 115: > 113: // javac -d <destDir> <javaFile> > 114: private static void compile(Path javaFile, Path destDir) throws > Exception { > 115: String javacPath = JDKToolFinder.getJDKTool("javac"); FYI. `jdk.test.lib.compiler.CompilerUtils` can be used to compile classes in process. ------------- Marked as reviewed by mchung (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/14395#pullrequestreview-1472770525 PR Review Comment: https://git.openjdk.org/jdk/pull/14395#discussion_r1224585461
