MuntashirAkon/AppManager · error · UnsupportedOperationException

Locking a remote file is not supported!

Error message

Locking a remote file is not supported!

What it means

RemoteFileChannel extends FileChannel to wrap a remote file, but POSIX-style file locking cannot be implemented over the remote-file transport, so lock() unconditionally throws UnsupportedOperationException. The library deliberately rejects the operation instead of silently misbehaving. Any blocking lock attempt on a remote file channel fails immediately.

Solutions

1. Remove the lock() call and use an application-level mutex/synchronization instead
2. Restrict locking code paths to local files only (check the file type before locking)
3. Use an alternative coordination mechanism such as a lock file on local storage

Example fix

// before
try (FileLock lck = channel.lock(0, Long.MAX_VALUE, false)) { ... }
// after
if (!(channel instanceof RemoteFileChannel)) {
    try (FileLock lck = channel.lock(0, Long.MAX_VALUE, false)) { ... }
} else {
    // app-level synchronization
}

boolean canLock = !(channel instanceof RemoteFileChannel);

boolean isRemoteChannel(FileChannel ch) { return ch instanceof RemoteFileChannel; }

try {
    channel.lock(0, Long.MAX_VALUE, false);
} catch (UnsupportedOperationException e) {
    // fall back to app-level synchronization
}

When it happens

Trigger: Calling FileChannel.lock(long,long,boolean) on a channel obtained for a remote file (e.g. via RemoteFile inputs), typically to coordinate exclusive access across processes.

Common situations: Code written for local files that uses lock() for atomic read-modify-write or to prevent concurrent modification, later run against a remote file path in App Manager's file abstraction.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Flags must be returned by the corresponding subclasses. key
• Invalid key
• Invalid key
• Invalid key
• Invalid key

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/d01393455b201fdd. Report an issue: GitHub.

Appendix: source

Thrown at libcore/io/src/main/java/io/github/muntashirakon/io/RemoteFileChannel.java:361

    @Override
    protected void implCloseChannel() {
        try { fs.close(handle); } catch (RemoteException ignored) {}
        synchronized (fdLock) {
            try { Os.close(read); } catch (ErrnoException ignored) {}
            try { Os.close(write); } catch (ErrnoException ignored) {}
        }
    }

    // Unsupported operations

    @Override
    public MappedByteBuffer map(MapMode mode, long position, long size) {
        throw new UnsupportedOperationException("Memory mapping a remote file is not supported!");
    }

    @Override
    public FileLock lock(long position, long size, boolean shared) {
        throw new UnsupportedOperationException("Locking a remote file is not supported!");
    }

    @Override
    public FileLock tryLock(long position, long size, boolean shared) {
        throw new UnsupportedOperationException("Locking a remote file is not supported!");
    }
}

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