On Tue, 11 May 2021 13:10:30 GMT, Aleksei Voitylov <avoity...@openjdk.org> wrote:
> Please review this PR which fixes the deadlock in ClassLoader between the two > lock objects - a lock object associated with the class being loaded, and the > ClassLoader.loadedLibraryNames hash map, locked during the native library > load operation. > > Problem being fixed: > > The initial reproducer demonstrated a deadlock between the JarFile/ZipFile > and the hash map. That deadlock exists even when the ZipFile/JarFile lock is > removed because there's another lock object in the class loader, associated > with the name of the class being loaded. Such objects are stored in > ClassLoader.parallelLockMap. The deadlock occurs when JNI_OnLoad() loads > exactly the same class, whose signature is being verified in another thread. > > Proposed fix: > > The proposed patch suggests to get rid of locking loadedLibraryNames hash map > and synchronize on each entry name, as it's done with class names in see > ClassLoader.getClassLoadingLock(name) method. > > The patch introduces nativeLibraryLockMap which holds the lock objects for > each library name, and the getNativeLibraryLock() private method is used to > lazily initialize the corresponding lock object. nativeLibraryContext was > changed to ThreadLocal, so that in any concurrent thread it would have a > NativeLibrary object on top of the stack, that's being currently > loaded/unloaded in that thread. nativeLibraryLockMap accumulates the names of > all native libraries loaded - in line with class loading code, it is not > explicitly cleared. > > Testing: jtreg and jck testing with no regressions. A new regression test > was developed. src/java.base/share/classes/jdk/internal/loader/NativeLibraries.java line 478: > 476: > 477: // thread local native libraries stack > 478: private static final ThreadLocal<Deque<NativeLibraryImpl>> > nativeLibraryThreadContext = I would prefer not see thread locals introduced here. We've put a lot of effort into recent releases to eliminate the use of TLs from java.base. ------------- PR: https://git.openjdk.java.net/jdk/pull/3976
