ADDITIONAL SYSTEM INFORMATION :
Windows is likely affected, too.

observed on Linux 6.8.0-51-generic #52~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Mon Dec 9 15:00:52 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
If multiple threads each instantiate their own java.util.zip.ZipFile instance using some java.nio.charset.Charset other than UTF_8 then they share the identical java.nio.charset.CharsetDecoder instance in Java 17, 21, 23, and 25 Build 5 (2025/1/9). The shared decoder is found following the private fields from ZipFile named res, zsrc, zc, dec. Iterating over the entries from both threads often yields an exception with the following stack trace (Java 17 in this case):

java.lang.IllegalStateException: Current state = RESET, new state = FLUSHED
at java.base/java.nio.charset.CharsetDecoder.throwIllegalStateException(CharsetDecoder.java:996)
at java.base/java.nio.charset.CharsetDecoder.flush(CharsetDecoder.java:679)
at java.base/java.nio.charset.CharsetDecoder.decode(CharsetDecoder.java:808)
at java.base/java.util.zip.ZipCoder.toString(ZipCoder.java:59)
at java.base/java.util.zip.ZipFile.getZipEntry(ZipFile.java:658)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.next(ZipFile.java:517)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.nextElement(ZipFile.java:505)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.nextElement(ZipFile.java:483)

Attached to this bug report you find a minimal example based on Charset.forName("IBM437"). Note that the example creates a temporary zip file using java.nio.file.Files#createTempFile. If everything works fine then both threads keep iterating forever. However, on affected Java versions, above IllegalStateException can be reproduced within a few seconds, which causes the program to terminate.

REGRESSION : Last worked in version 11.0.25

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the following command with an affected Java version (17, 21, 23, or 25 Build 5 (2025/1/9)) on Linux:

java ZipFileMultithreadingExample.java

Windows is likely to be affected, too (untested).

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The program runs forever (as it does with unaffected Java 11).
ACTUAL -
The program prints the following stack trace and stops:

java.lang.IllegalStateException: Current state = RESET, new state = FLUSHED
at java.base/java.nio.charset.CharsetDecoder.throwIllegalStateException(CharsetDecoder.java:996)
at java.base/java.nio.charset.CharsetDecoder.flush(CharsetDecoder.java:679)
at java.base/java.nio.charset.CharsetDecoder.decode(CharsetDecoder.java:808)
at java.base/java.util.zip.ZipCoder.toString(ZipCoder.java:59)
at java.base/java.util.zip.ZipFile.getZipEntry(ZipFile.java:658)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.next(ZipFile.java:517)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.nextElement(ZipFile.java:505)
at java.base/java.util.zip.ZipFile$ZipEntryIterator.nextElement(ZipFile.java:483)
at ZipFileMultithreadingExample.iterateZipEntries(ZipFileMultithreadingExample.java:118)
at ZipFileMultithreadingExample.keepIteratingZipEntries(ZipFileMultithreadingExample.java:105)
at ZipFileMultithreadingExample.lambda$main$0(ZipFileMultithreadingExample.java:49)
at java.base/java.lang.Thread.run(Thread.java:840)

---------- BEGIN SOURCE ----------
import static java.lang.Thread.currentThread;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.nio.file.Files.createTempFile;
import static java.util.Arrays.asList;
import static java.util.Collections.synchronizedList;
import static java.util.stream.Collectors.toList;

import java.io.IOException;
import java.io.OutputStream;
import java.io.UncheckedIOException;
import java.lang.reflect.Field;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.attribute.FileTime;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.stream.Stream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.util.zip.ZipOutputStream;

public class ZipFileMultithreadingExample {
  private static final Charset IBM_437 = Charset.forName("IBM437");

  /**
   * @apiNote Tested with Java 17, 21, 23, and 25 Build 5 (2025/1/9). It is NOT required to
   * reproduce the bug, but it helps to understand what is going on. Needs the following VM
   * option: --add-opens java.base/java.util.zip=ALL-UNNAMED
   */
  private static final boolean PRINT_DEBUG_INFO_SHOWING_MULTITHREADED_USAGE_OF_DECODER = false;

  public static void main(String[] args) throws Exception {
    int numberOfThreads = 2;
    int numberOfEntries = 64;

    Path zip = createTempFile(ZipFileMultithreadingExample.class.getSimpleName() + ".", ".zip");
    zip.toFile().deleteOnExit();
    fillZipWithEntries(zip, numberOfEntries);

    CyclicBarrier before = new CyclicBarrier(numberOfThreads + 1);
    CyclicBarrier after = new CyclicBarrier(numberOfThreads + 1);
    List<Throwable> problems = synchronizedList(new ArrayList<>());

    Runnable runnable = () -> keepIteratingZipEntries(before, after, zip, problems);

    List<Thread> threads =
        Stream.generate(() -> new Thread(runnable)).limit(numberOfThreads).collect(toList());

    for (Thread thread : threads) thread.start();

    int counter = 0;
    while (problems.isEmpty()) {
      before.await();
      after.await();
      System.out.println(counter + " " + problems.size());
      ++counter;
    }

    for (Thread thread : threads) thread.interrupt();
    for (Thread thread : threads) thread.join();

    for (Throwable problem : problems) {
      problem.printStackTrace();
    }
  }

  private static void fillZipWithEntries(Path dstFile, int numberOfEntries) throws IOException {
    FileTime now = FileTime.from(Instant.now());
    try (OutputStream outputStream = Files.newOutputStream(dstFile);
        ZipOutputStream zipOutputStream = new ZipOutputStream(outputStream, IBM_437)) {
      while (numberOfEntries-- > 0) {
        String uuidString = UUID.randomUUID().toString();

        String name =
            String.join(
                "/",
                asList(
                    uuidString.substring(0, 2), //
                    uuidString.substring(2, 4),
                    uuidString.substring(4) + ".txt"));

        ZipEntry zipEntry = new ZipEntry(name);
        zipEntry.setCreationTime(now); // Java needs times for proper UTF-8 support
        zipEntry.setLastModifiedTime(now);
        zipEntry.setLastAccessTime(now);

        zipOutputStream.putNextEntry(zipEntry);
        zipOutputStream.write(uuidString.getBytes(UTF_8));
        zipOutputStream.write('\n');
        zipOutputStream.closeEntry();
      }
    }
  }

  private static void keepIteratingZipEntries(
      CyclicBarrier before, CyclicBarrier after, Path zip, List<Throwable> problems) {
    while (!currentThread().isInterrupted()) {
      if (!tryAwait(before)) return;
      try {
        iterateZipEntries(zip);
      } catch (Throwable t) {
        problems.add(t);
      }
      if (!tryAwait(after)) return;
    }
  }

  private static void iterateZipEntries(Path zip) {
    try (ZipFile zipFile = new ZipFile(zip.toFile(), IBM_437)) {
      if (PRINT_DEBUG_INFO_SHOWING_MULTITHREADED_USAGE_OF_DECODER) printDebugInfo(zipFile);
      Enumeration<? extends ZipEntry> entries = zipFile.entries();
      while (entries.hasMoreElements()) {
        entries.nextElement();
      }
    } catch (IOException e) {
      throw new UncheckedIOException(e);
    }
  }

  @SuppressWarnings("BooleanMethodIsAlwaysInverted")
  private static boolean tryAwait(CyclicBarrier after) {
    try {
      after.await();
      return true;
    } catch (BrokenBarrierException e) {
      return false;
    } catch (InterruptedException e) {
      currentThread().interrupt();
      return false;
    }
  }

  private static void printDebugInfo(ZipFile zipFile) {
    try {
      Field resField = ZipFile.class.getDeclaredField("res");
      resField.setAccessible(true);
      Object res = resField.get(zipFile);
      Field zsrcField = res.getClass().getDeclaredField("zsrc");
      zsrcField.setAccessible(true);
      Object zsrc = zsrcField.get(res);
      Field zcField = zsrc.getClass().getDeclaredField("zc");
      zcField.setAccessible(true);
      Object zc = zcField.get(zsrc);
      Field decField = zc.getClass().getDeclaredField("dec");
      decField.setAccessible(true);
      Object dec = decField.get(zc);
      System.out.println(currentThread() + " uses " + dec);
    } catch (Throwable t) {
      System.out.println(
          "Failed to print debug info. In Java 17, 21, 23, and 25 Build 5 (2025/1/9), the following"
              + " VM option is required: --add-opens java.base/java.util.zip=ALL-UNNAMED"
              + (" - Original error: " + t));
    }
  }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
There are multiple possibilities for avoiding this bug:
- use Java 11
- use StandardCharsets#UTF_8 as the second argument of the ZipFile constructor (or omit the argument)
- externally synchronize access to all ZipFile instances

I believe that also the following helps (do to internal synchronization Based on ZipFile.this):
- Share the identical ZipFile instance among all participating threads. Note that in the example, each thread creates its own ZipFile instance to the same zip file on disk.


FREQUENCY : often