问题
I developing a SpringBoot-Application. During stress-testing the application shows some strange behaviour according parallel execution. AFAIK there should not be some parallel execution...
To test this behaviour i created this RestController:
@RestController
public class TestController2 {
private static int instancecount = 0;
@PostConstruct
public void con() {
System.out.println("instancecount: " + ++instancecount);
}
@PreDestroy
public void des() {
System.out.println("PreDestroy");
}
@RequestMapping(value = { "/", "/**" }, method = RequestMethod.GET)
@ResponseBody
public ResponseEntity<String> entrypoint(@RequestHeader Map<String, String> requestHeaders) {
System.out.println("PRE!!!!!!!!!!!!!");
try {
Thread.sleep(120000);
} catch (InterruptedException e) {
}
System.out.println("POST!!!!!!!!!!!!!!!!!");
return new ResponseEntity<String>("qwertz", null, HttpStatus.OK);
}
}
The application compiles and works like expected. Now i open the browser with 14 tabs simultaneously.
In the log i can see instant:
PRE!!!!!!!!!!!!!
after approximately 15 sek. the next 5: PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!!
After 2 minutes the first finished. The other 5 finished at ~2:15.
This repeats until every 14 tabs are finished.
and now my question:
- Why is there a parallel execution?
- Why 6?
- Why the second starts after ~15 seconds?
I am a little bit confused. I don't know where or what i have to look for?
Need input!
THX
回答1:
In the log i can see instant:
PRE!!!!!!!!!!!!!
after approximately 15 sek. the next 5: PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!! PRE!!!!!!!!!!!!!
I think this is a problem / limitation from the browser.
When a request arrives to the servlet container (Tomcat for an example), a thread is retrieved from the pool to serve it. This means that the each request has it's own thread and it will work with this thread during it's whole lifecycle (i.e: you sent a response).
That's why I think this is a limitation imposed by the browser.
Take a look:
@RestController
@RequestMapping(path = "test")
public class TestController {
private final Logger log = LoggerFactory.getLogger(this.getClass());
@GetMapping
public ResponseEntity<Object> handleTest() throws InterruptedException {
log.info("Thread {} started", Thread.currentThread().toString());
Thread.sleep(5000);
log.info("Thread {} finished", Thread.currentThread().toString());
return ResponseEntity.ok("EXECUTED!!");
}
}
First test
5 opened tabs in the browser
This gets logged instantly
2019-10-17 09:36:37.514 INFO 10324 --- [nio-8083-exec-1] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-1,5,main] started
Now, after all 5 request (5 tabs) receive a response (take a look at the time - one is executed after another):
2019-10-17 09:36:37.514 INFO 10324 --- [nio-8083-exec-1] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-1,5,main] started
2019-10-17 09:36:42.515 INFO 10324 --- [nio-8083-exec-1] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-1,5,main] finished
2019-10-17 09:36:42.551 INFO 10324 --- [nio-8083-exec-2] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-2,5,main] started
2019-10-17 09:36:47.551 INFO 10324 --- [nio-8083-exec-2] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-2,5,main] finished
2019-10-17 09:36:47.559 INFO 10324 --- [nio-8083-exec-4] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-4,5,main] started
2019-10-17 09:36:52.560 INFO 10324 --- [nio-8083-exec-4] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-4,5,main] finished
2019-10-17 09:36:52.571 INFO 10324 --- [nio-8083-exec-5] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-5,5,main] started
2019-10-17 09:36:57.572 INFO 10324 --- [nio-8083-exec-5] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-5,5,main] finished
2019-10-17 09:36:57.582 INFO 10324 --- [nio-8083-exec-6] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-6,5,main] started
2019-10-17 09:37:02.584 INFO 10324 --- [nio-8083-exec-6] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-6,5,main] finished
Second test
Refreshing the page in the browser
Go ahead, open your browser, type the URL, press ENTER and start pressing CTRL + R.
I pressed CTRL + R four times.
So there will be 1 + 4 request (the first (with ENTER) and the subsequent 4 requests (with CTRL + R))
I can see that all 5 threads start running in parallel:
2019-10-17 09:46:30.149 INFO 10324 --- [nio-8083-exec-9] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-9,5,main] started
2019-10-17 09:46:30.471 INFO 10324 --- [io-8083-exec-28] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-28,5,main] started
2019-10-17 09:46:30.713 INFO 10324 --- [io-8083-exec-29] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-29,5,main] started
2019-10-17 09:46:30.981 INFO 10324 --- [io-8083-exec-10] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-10,5,main] started
2019-10-17 09:46:31.244 INFO 10324 --- [nio-8083-exec-1] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-1,5,main] started
Third test
Using two different clients
Go ahead, try with Postman (or any other http client) and with your browser.
Send a request with the browser, ALT + TAB and send the request with Postman.
I can see that the two threads start running in paralel (first request was from the browser and the second request were made using Postman):
2019-10-17 09:50:31.663 INFO 10324 --- [nio-8083-exec-5] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-5,5,main] started
2019-10-17 09:50:32.587 INFO 10324 --- [nio-8083-exec-9] b.c.d.m.controller.TestController : Thread Thread[http-nio-8083-exec-9,5,main] started
By seeing these tests, I'm convinced that this is a limitation imposed by the browser.
来源：https://stackoverflow.com/questions/58432195/spring-restcontroller-6-parallel-execution