Is there any thread limit on CompletableFuture.runAsync

Question

I have a Rest api, in which it calls a async call like below

 CompletableFuture.runAsync(() -> {
                        // method call or code to be async.
                     try {
                            logger.info("======Before Async method call======with studySchemaEventId: "+enrollmentStudySchemaEventId);
                            this.performSimulation(studyId, enrollmentStudySchemaEventId, cloneOfFile, simulationRunInfo, totalAccrual);
                            logger.info("======After Async method call======with studySchemaEventId: "+enrollmentStudySchemaEventId);
                        } catch (SimulationException e) {
                            logger.error("Error running Async call for performSimulation()", e);
                        }
                    });

when i call Rest api, it executed async call correctly. But i have a case where i called Rest Api, 4 times and it executed Async call for 3 and for the 4th Api call i dont see Async method being called.

Is there any limit on runAsync() call ? or why is it not calling Async method after 3 calls ?

Here is the Rest API call:

    @POST
    @Path("/trigger")
    @Consumes(MediaType.MULTIPART_FORM_DATA)  
    @ApiOperation(value = "Trigger Simulation",  tags = "Study Event Simulation")
    public Response triggerSimulation( 
            @FormDataParam("file") InputStream file,
            @FormDataParam("file") FormDataContentDisposition fileDetail ,
            @FormDataParam("simulationRunInfo") SimulationRunInfo simulationRunInfo
  
    ) 
    {

// some other logic
// Async code here

}

Answer 1

What you have encountered is the number of threads configured in the ForkJoinPool.commonPool().

The task assigned to runAsSync is completed by the ForkJoinPool.commonPool(). This pool is configured on the basis of the number of cores in your host computer. It seems that you have 4 cores.

By default, the size of the common pool:

Runtime.getRuntime().availableProcessors() - 1

You can update the size:

-Djava.util.concurrent.ForkJoinPool.common.parallelism=8

Alternatively you can use the overloaded runAsSync with the executors argument.