On Fri, 9 Jun 2023 14:55:50 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 to reliably use th... src/java.base/share/classes/jdk/internal/loader/URLClassPath.java line 186: > 184: * @apiNote Used to create the application class path. > 185: */ > 186: URLClassPath(String cp, URLStreamHandler jarHandler, boolean > skipEmptyElements) { This is a special constructor for the application class path so shouldn't have the jarHandle parameter. This should allow you to drop the changes to ClassLoaders. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/14395#discussion_r1224427082
