RFR: 8289643: File descriptor leak with ProcessBuilder.startPipeline [v2]

[David Schlosnagle]

On Fri, 8 Jul 2022 16:24:16 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> The `ProcessBuilder.pipelineStart()` implementation does not close all of the file descriptors it uses to create the pipeline of processes.
>> 
>> The process calling `pipelineStart()` is creating the pipes between the stages.
>> As each process is launched, the file descriptor is inherited by the child process and
>> the child process `dup`s them to the respective stdin/stdout/stderr fd.  
>> These copies of inherited file descriptors are handled correctly.
>> 
>> Between the launching of each Process, the file descriptor for the read-side of the pipe for the output of the previous process is kept open (in the parent process invoking `pipelineStart`).  The file descriptor is correctly passed to the child and is dup'd to the stdin of the next process.
>> 
>> However, the open file descriptor in the parent is not closed after it has been used as the input for the next Process. 
>> The fix is to close the fd after it has been used as the input of the next process.
>> 
>> A new test verifies that after `pipelineStart` is complete, the same file descriptors are open for Unix Pipes as before the test.
>> The test only runs on Linux using the /proc/<pid>/fd filesystem to identify open file descriptors.
>> 
>> The bug fix is in `ProcessBuilder.pipelineStart` and is applicable to all platforms.
>
> Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanup of PipelineLeaksFD test improving error messages and source cleanup.

test/jdk/java/lang/ProcessBuilder/PipelineLeaksFD.java line 130:

> 128:                 })
> 129:                 .filter(p1 -> p1.link().toString().startsWith("pipe:"))
> 130:                 .collect(Collectors.toSet());

Is this intentionally leaking the returned `DirectoryStream` from `Files.walk` to  trigger the previous failure mode or should this be auto-closed (i.e. https://errorprone.info/bugpattern/StreamResourceLeak )?

Suggestion:

        try (Stream<Path> s = Files.walk(path)) {
            return s.filter(Files::isSymbolicLink)
                    .map(p -> {
                        try {
                            return new PipeRecord(p, Files.readSymbolicLink(p));
                        } catch (IOException ioe) {
                        }
                        return new PipeRecord(p, null);
                    })
                    .filter(p1 -> p1.link().toString().startsWith("pipe:"))
                    .collect(Collectors.toSet());
        }

-------------

PR: https://git.openjdk.org/jdk/pull/9414