Executing multiple findMap query in parallel - Thread safe ?

[AntoineDuComptoirDesPharmacies]

Hi everyone,

Our objective is to run two query in parallel but we want the result being keyed in a Map.
We could have used findFutureList but it means doing the Map ourselves.
So we are wondering if it is safe to call multiple QueryBean findMap method in parallel, without concurrency problems ?

For example :

    public Map<Long, Stock> getMapSortedByProductId(Long userId, Set<Long> productIds) {
        return new QStock()
                .id.userId.eq(userId)
                .id.productId.in(productIds)
                .setMapKey("id.productId")
                .findMap();
    }

    public Map<Long, ProductSynchronization> getMapSortedByProductId(Long userId, Set<Long> productIds) {
        return new QProductSynchronization()
                .id.userId.eq(userId)
                .id.productId.in(productIds)
                .setMapKey("id.productId")
                .findMap();
    }

        CompletableFuture<Map<Long, ProductSynchronization>> futureMapOfProductSynchronizationByProductId = CompletableFuture.supplyAsync(() ->
                this.produdctSynchronizationRepository.getMapSortedByProductId(userId, productIds)
        );

        CompletableFuture<Map<Long, Stock>> futureMapOfStockByProductId = CompletableFuture.supplyAsync(() ->
                this.stockRepository.getMapSortedByProductId(userId, productIds)
        );

         CompletableFuture.allOf(futureMapOfProductSynchronizationByProductId, futureMapOfStockByProductId)
                    .thenAccept(v -> {
                 [...]
          })

We are affraid of any random issue with shared objects during the query preparation/run.

Thanks in advance for your help.
Yours faithfully,
LCDP

[rPraml]

As far as I remember findFuture may be removed with ebean 15. So using findMapnis totally OK and yes, this is thread safe, if you use distinct query objects (what yout example does)

If you prepare a query in main thread, you always can call 'query.copy()', to get a new query object.

We do these kind of async queries as our daily business. We use 'DB.backgroundExecutor()' to get a Future, by submitting callable.

Things to pay attention:

• Depending on your use case, you may implement some rate limit (e. g. limit to 10 background queries with a semaphore) otherwise...
• You need a large enough connection pool.
• if you use threadlocals (currentUser, currentTenanat) , you must copy them (Take a look at BackgroundExecutorWrapper)

[rbygrave]

findFuture may be removed with ebean 15

Note that findFuture queries will stay, they will not be removed from 15.

Background: They initially were removed in 15.0.0, then almost immediately I hit a person with a use case and realised that it was good to keep the findFuture support as a first class feature so it got restored in version 15.0.1 - https://github.com/ebean-orm/ebean/releases/tag/15.0.1 ... and we will keep findFuture going forward.

[thomas-lcdp]

We propose to implement a findFutureMap instead of use the CompletableFuture

#3593