spotBugs and JDK-8194978: Javac produces dead code for try-with-resource (original) (raw)

Enrico Olivelli eolivelli at gmail.com
Fri Nov 9 16:16:15 UTC 2018

Hi, I am in the same situation, I should add that from JDK9 the try-with-resources block added a $closeResource method, which I can't find in the example from Ismael

see for reference another know problem with Spotbugs https://github.com/spotbugs/spotbugs/issues/493

Any help or clarification will be appreciated

Thanks Enrico

Il giorno ven 9 nov 2018 alle ore 16:24 Ismael Juma <mlists at juma.me.uk> ha scritto:

Any comments on this? Many people are disabling spotBugs when compiling with Java 11 due to this issue: https://github.com/spotbugs/spotbugs/issues/756 Ismael On Thu, Sep 13, 2018 at 10:05 PM Ismael Juma <mlists at juma.me.uk> wrote:

Hi all, JDK-8194978 introduced some changes to the bytecode generated by javac for the try with resource construct. In the following code, it seems to generate a null check on a reference after invoking a method on it: public static void readFileAsString(String path) throws IOException { try (FileChannel fc = FileChannel.open(Paths.get(path))) { fc.size(); } } In line 16 to 22 of the bytecode, it looks like we check for null after calling a method on the fc reference: 16: aload1 17: invokevirtual #6 // Method java/nio/channels/FileChannel.size:()J 20: pop2 21: aload1 22: ifnull 52 25: aload1 26: invokevirtual #7 // Method java/nio/channels/FileChannel.close:()V Is this intentional? I ask because this pattern triggers a spotBugs warning since it often implies a bug in user's code: RCN | Nullcheck of fc at line 10 of value previously dereferenced in TryTest.readFileAsString(String, Charset) Note that this works fine in Java versions older than Java 11. Since this spotBugs warning is generally useful, it would be handy if javac did not trigger it. Alternatively, if there's a good way to detect the code that was generated by javac, spotBugs could be updated to ignore it. For reference, this was discussed in the spotBugs issue tracker: https://github.com/spotbugs/spotbugs/issues/756 And method bytecode in full: public static void readFileAsString(java.lang.String) throws java.io.IOException; Code: 0: aload0 1: iconst0 2: anewarray #2 // class java/lang/String 5: invokestatic #3 // Method java/nio/file/Paths.get:(Ljava/lang/String;[Ljava/lang/String;)Ljava/nio/file/Path; 8: iconst0 9: anewarray #4 // class java/nio/file/OpenOption 12: invokestatic #5 // Method java/nio/channels/FileChannel.open:(Ljava/nio/file/Path;[Ljava/nio/file/OpenOption;)Ljava/nio/channels/FileChannel; 15: astore1 16: aload1 17: invokevirtual #6 // Method java/nio/channels/FileChannel.size:()J 20: pop2 21: aload1 22: ifnull 52 25: aload1 26: invokevirtual #7 // Method java/nio/channels/FileChannel.close:()V 29: goto 52 32: astore2 33: aload1 34: ifnull 50 37: aload1 38: invokevirtual #7 // Method java/nio/channels/FileChannel.close:()V 41: goto 50 44: astore3 45: aload2 46: aload3 47: invokevirtual #9 // Method java/lang/Throwable.addSuppressed:(Ljava/lang/Throwable;)V 50: aload2 51: athrow 52: return Exception table: from to target type 16 21 32 Class java/lang/Throwable 37 41 44 Class java/lang/Throwable Thanks, Ismael

More information about the compiler-dev mailing list