Integrated: 8193513: add support for printing a stack trace on class loading

[Doug Simon]

On Tue, 20 Jun 2023 09:19:42 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> In the development of libgraal, it has been very useful to see why a given class is loaded (e.g., trying to reduce startup time by avoiding unnecessary eager class loading). One way to do this is to see the stack trace when the VM loads a class. The only possibility currently is to add a static initializer to the class of interest. However, not only is this not always possible but it doesn't correlate with class loading but with class initialization.
> 
> This PR adds support for `-Xlog:class+load+cause` and `-Xlog:class+load+cause+native` that produce output according to a new `LogClassLoadingCauseFor` VM flag:
> 
> 
>   product(ccstr, LogClassLoadingCauseFor, nullptr,                          \
>           "Apply -Xlog:class+load+cause* to classes whose fully "           \
>           "qualified name contains this string ("*" matches "             \
>           "any class).")                                                    \
> 
> 
> Example usage:
> 
> java "-Xlog:class+load+cause*" -XX:LogClassLoadingCauseFor=java.util.concurrent.ConcurrentHashMap$V --version
> [0.075s][info][class,load,cause] Java stack when loading java.util.concurrent.ConcurrentHashMap$ValuesView:
> [0.075s][info][class,load,cause] 	at java.util.concurrent.ConcurrentHashMap.values(java.base/ConcurrentHashMap.java:1263)
> [0.075s][info][class,load,cause] 	at jdk.internal.loader.NativeLibraries.find(java.base/NativeLibraries.java:102)
> [0.075s][info][class,load,cause] 	at java.lang.ClassLoader.findNative(java.base/ClassLoader.java:2457)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.UnixNativeDispatcher.init(java.base/Native Method)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.UnixNativeDispatcher.<clinit>(java.base/UnixNativeDispatcher.java:817)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.UnixFileSystem.<init>(java.base/UnixFileSystem.java:96)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.BsdFileSystem.<init>(java.base/BsdFileSystem.java:50)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.MacOSXFileSystem.<init>(java.base/MacOSXFileSystem.java:52)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.MacOSXFileSystemProvider.newFileSystem(java.base/MacOSXFileSystemProvider.java:44)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.MacOSXFileSystemProvider.newFileSystem(java.base/MacOSXFileSystemProvider.java:37)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.UnixFileSystemProvider.<init>(java.base/UnixFileSystemProvider.java:78)
> [0.075s][info][class,load,cause] 	at sun.nio.fs.BsdFileSystemProvider.<init>(java.b...

This pull request has now been integrated.

Changeset: 4a1fcb60
Author:    Doug Simon <dnsimon at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/4a1fcb6063fd5fad9ff9763359e7c79401e4fa92
Stats:     110 lines in 6 files changed: 105 ins; 0 del; 5 mod

8193513: add support for printing a stack trace on class loading

Reviewed-by: dholmes, iklam, coleenp

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PR: https://git.openjdk.org/jdk/pull/14553