So there is some table that can only have unique values. I want to read or create new value. I though this would be fairly simple, but for some reason synchronized is not working for me… Maybe it’s just the hot summer day and I’m missing something simple 😉

The error thrown when two threads try to create the same signature:

Caused by: org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique

I’m working with JDK17, Hibernate5, Spring5 (not migrating to Jakarta yet).

// update that needs to be isolated or it throws constraint violation upon creating duplicate signature
private void updateSignature(HoldingEntity holding, String signature) {
    var signatureInDb = signatureDAO.getByText(signature);

    SignatureEntity newSignature = null;
    if (signatureInDb != null) {
        newSignature = signatureInDb;
    } else {
        newSignature = new signatureEntity();
        newSignature.setText(signature);
        signatureDAO.create(newSignature);
    }

    holding.setSignature(newSignature);
}

As you can imagine updateSignature is a part of a larger service that creates holdings.

    @Transactional(rollbackFor = {Throwable.class})
    public HoldingEntity create(HoldingParams params)
            throws HoldingServiceException {
        // ...
        updateSignature(holding, signature);
        // ...
    }

Simplified import thread creation:

public void executeImport(Long jobId, String importType, ImportHelperThread importHelperThread) {
    // setup sub-threads
    ExecutorService executor = Executors.newFixedThreadPool(splitThreadCount);
    CompletionService<Void> completionService = new ExecutorCompletionService<>(executor);

    // run sub-threads
    for (int i = 0; i < splitThreadCount; i++) {
        final int threadIndex = i;
        completionService.submit(() -> {
            try {
                initImportThread(jobId);
                importHelperThread.run(threadIndex);
            } finally {
                ThreadContextHolder.clear();
            }
            return null;
        });
    }

    // stop accepting new subtasks
    executor.shutdown();
    executor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
}