[External] : Re: VirtualMachineImpl.checkCatchesAndSendQuitTo leaks file handles

[Laurence Cable]

ignore this... apologies

On 5/29/25 11:51 AM, Laurence Cable wrote:
> https://github.com/openjdk/jdk/pull/25526
>
> On 5/29/25 11:05 AM, Kevin Walls wrote:
>> OK thanks Philippe, and Larry -
>>
>> I can't provoke a problem as it stands but yes it would be good to 
>> take the recommendation of the API Note, that should keep us 
>> efficient. 8-)
>>
>> I created a JBS issue: https://bugs.openjdk.org/browse/JDK-8358088
>>
>> Thanks!
>> Kevin
>> ------------------------------------------------------------------------
>> *From:* Philippe Marschall <kustos at gmx.net>
>> *Sent:* Thursday, May 29, 2025 5:47 PM
>> *To:* Kevin Walls <kevin.walls at oracle.com>; 
>> serviceability-dev at openjdk.java.net <serviceability-dev at openjdk.java.net>
>> *Subject:* [External] : Re: 
>> VirtualMachineImpl.checkCatchesAndSendQuitTo leaks file handles
>>
>>
>>
>> On 29.05.25 12:21, Kevin Walls wrote:
>> > Hi --
>> >
>> > Just to be clear, is this an actual persistent leak that we can 
>> observe, or is it that we could close earlier with try-with-resources?
>> > I'm not seeing a leak when calling a line like this over and over 
>> in a tight loop:
>> >    final var cmdline = Files.lines(path).findFirst();
>>
>> I believe it is persistent until the Cleaner of FileChannel closes it.
>> The #line Javadoc [1] mentions the need to close
>>
>>  > This method must be used within a try-with-resources statement or
>>  > similar control structure to ensure that the stream's open file is
>>  > closed promptly after the stream's operations have completed.
>>
>> The Stream class Javadoc [2] explicitly mentions #lines as well
>>
>>  > Generally, only streams whose source is an IO channel, such as those
>>  > returned by Files.lines(Path), will require closing. If a stream does
>>  > require closing, it must be opened as a resource within a
>>  > try-with-resources statement or similar control structure to ensure
>>  > that it is closed promptly after its operations have completed.
>>
>> If I run something like the code below I get
>> java.nio.file.FileSystemException: marker: Too many open files. You can
>> also lower the number, set a breakpoint at System.out.println and check
>> /proc/<pid>/fd
>>
>>
>> Path marker = Path.of("marker");
>> if (!Files.exists(marker)) {
>>    Files.writeString(marker, "line1");
>> }
>> // usually over the max fd limit
>> int fileCount = 100_000;
>> // prevent streams from being garbage collected and cleaner to run and
>> close fd
>> List<Stream<?>> streams = new ArrayList<>(fileCount);
>> for (int i = 0; i < fileCount; i++) {
>>    Stream<String> stream = Files.lines(marker);
>>    streams.add(stream);
>>    Optional<String> firstLine = stream.findFirst();
>>    if (firstLine.isPresent()) {
>>      if (firstLine.get().hashCode() == 42) {
>>        System.out.println('x');
>>      }
>>    }
>> }
>> System.out.println(streams.hashCode());
>>
>>   [1]
>> https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/nio/file/Files.html#lines(java.nio.file.Path) 
>>
>>   [2]
>> https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/stream/Stream.html 
>>
>>
>> Regards
>> Philippe
>
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