On Fri, 15 Nov 2024 20:54:56 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
> DirectByteBuffers are still using old `jdk.internal.ref.Cleaner` > implementation. That implementation carries a doubly-linked list, and so > makes DBB suffer from the same issue fixed for generic > `java.lang.ref.Cleaner` users with > [JDK-8343704](https://bugs.openjdk.org/browse/JDK-8343704). See the bug for > the reproducer. > > We can migrate DBBs to use `java.lang.ref.Cleaner`. > > There are two pecularities during this rewrite. > > First, the old ad-hoc `Cleaner` implementation used to exit the VM when > cleaning action failed. I presume it was to avoid memory leak / accidental > reuse of the buffer. I moved the relevant block to `Deallocator` directly. > Unfortunately, I cannot easily test it. > > Second is quite a bit hairy. Old DBB cleaning code was hooked straight into > `Reference` processing loop. This was possible because we could infer that > the weak references we are processing were DBB cleaning actions, since old > `Cleaner` was the only use of this code. With standard `Cleaner`, we have > lost this association, and so we cannot really do this from the reference > processing loop. With the patched version, we now rely on normal `Cleaner` > thread to do cleanups for us. Because of this, there is a new outpacing > opportunity window where reference processing might have been over, but > cleaner thread has not reacted yet. > > Tests show that DirectBufferAlloc tests are still surviving this, possibly > due to exponential sleep-backoff already built in. See the reclamation path > in `Bits.unreserveMemory`: > https://github.com/openjdk/jdk/blob/c207cc7e705d3f449f2387324d86cfb31ce40c44/src/java.base/share/classes/java/nio/Bits.java#L106-L186 > > Additional testing: > - [x] Linux x86_64 server fastdebug, `java/nio java/io` > - [x] Linux AArch64 server fastdebug, `java/nio java/io` > - [ ] Linux x86_64 server fastdebug, `all` > - [ ] Linux AArch64 server fastdebug, `all` FTR, wider testing shows two tests that install custom system classloader fail with the following circularity: TEST: runtime/cds/appcds/SpecifySysLoaderProp.java TEST: java/security/SignedJar/SignedJarWithCustomClassLoader.java Caused by: java.lang.IllegalStateException: getSystemClassLoader cannot be called during the system class loader instantiation at java.lang.ClassLoader.getSystemClassLoader(java.base@25-internal/ClassLoader.java:1849) at jdk.internal.misc.InnocuousThread.newThread(java.base@25-internal/InnocuousThread.java:68) at jdk.internal.ref.CleanerImpl$InnocuousThreadFactory.newThread(java.base@25-internal/CleanerImpl.java:208) at jdk.internal.ref.CleanerImpl.start(java.base@25-internal/CleanerImpl.java:110) at java.lang.ref.Cleaner.create(java.base@25-internal/Cleaner.java:174) at java.nio.DirectByteBuffer.<clinit>(java.base@25-internal/DirectByteBuffer.java:95) at jdk.internal.perf.Perf.createLong(java.base@25-internal/Native Method) at jdk.internal.perf.PerfCounter.<init>(java.base@25-internal/PerfCounter.java:63) at jdk.internal.perf.PerfCounter.newPerfCounter(java.base@25-internal/PerfCounter.java:69) at jdk.internal.perf.PerfCounter$CoreCounters.<clinit>(java.base@25-internal/PerfCounter.java:126) at jdk.internal.perf.PerfCounter.getZipFileOpenTime(java.base@25-internal/PerfCounter.java:176) at java.util.zip.ZipFile.<init>(java.base@25-internal/ZipFile.java:203) at java.util.zip.ZipFile.<init>(java.base@25-internal/ZipFile.java:148) at java.util.jar.JarFile.<init>(java.base@25-internal/JarFile.java:333) at jdk.internal.loader.URLClassPath$JarLoader.getJarFile(java.base@25-internal/URLClassPath.java:682) at jdk.internal.loader.URLClassPath$JarLoader.ensureOpen(java.base@25-internal/URLClassPath.java:653) at jdk.internal.loader.URLClassPath$JarLoader.<init>(java.base@25-internal/URLClassPath.java:622) at jdk.internal.loader.URLClassPath.getLoader(java.base@25-internal/URLClassPath.java:465) at jdk.internal.loader.URLClassPath.getLoader(java.base@25-internal/URLClassPath.java:409) at jdk.internal.loader.URLClassPath.getResource(java.base@25-internal/URLClassPath.java:331) at jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(java.base@25-internal/BuiltinClassLoader.java:688) at jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(java.base@25-internal/BuiltinClassLoader.java:620) at jdk.internal.loader.BuiltinClassLoader.loadClass(java.base@25-internal/BuiltinClassLoader.java:578) at java.lang.ClassLoader.loadClass(java.base@25-internal/ClassLoader.java:490) at java.lang.Class.forName0(java.base@25-internal/Native Method) at java.lang.Class.forName(java.base@25-internal/Class.java:543) at java.lang.ClassLoader.initSystemClassLoader(java.base@25-internal/ClassLoader.java:1887) at java.lang.System.initPhase3(java.base@25-internal/System.java:1964) This can be avoided if we use the lazy holder pattern to delay `Cleaner` initialization until the actual use. Done in new commit. ------------- PR Comment: https://git.openjdk.org/jdk/pull/22165#issuecomment-2602865622
