Correct way to wait for some task to complete in the http post request

[crl-manoj]

Hi, Currently I have a function "A" which waits using this_thread:sleep_for(..) until some condition is met. And I am calling the function "A" inside the http post request before sending the response. Is this correct way or there is some other way to wait for this function?
I am also using C++17

[an-tao]

The sleep_for function blocks current thread, that's not a good operation. please use some async timer instead. such as the loop->runAfter() method or the sleepCoro coroutine.

[crl-manoj]

@an-tao Thank you for the response. We are using C++17 so I looked into the loop->runAfter() only thing is let's say we do app().getLoop()->runAfter(5, { /* some ops */});
The another request that I'm waiting on might already complete after 1 second, but I still won't be able to respond for 5 seconds.

[an-tao]

Async timer should not affect other requests, I need more details of your usage scenario, better if you can share relevant code

[crl-manoj]

Async timer should not affect other requests, I need more details of your usage scenario, better if you can share relevant code
@an-tao
sendParam is the http post request and the getRName(..) method is where I'm doing the thread sleep_for call.

#include "ZMQOpts.h"
#include <string.h>
#include <zmq.h>

using namespace v1;

void params::sendParams(const HttpRequestPtr &req,
                        std::function<void(const HttpResponsePtr &)> &&callback,
                        int num) const {
  auto data = std::string(req->getBody());
  Json::Value root;
  Json::Reader reader;
  bool success = reader.parse(data, root);
  if (!success) {
    throw InvalidReqException("Invalid body");
  }

  int timeoutSec = getTimeout(root);

  auto response = ZMQ_SendReqs(num, SEND_PARAM, root);

  auto jsonRsp = createJsonResp(response);

  jsonRsp["rname"] = getRName(num, timeoutSec);

  auto resp = HttpResponse::newHttpJsonResponse(jsonRsp);
  resp->setStatusCode(k200OK);
  callback(resp);
}

std::string params::getRName(int num, int timeoutSec) const {
  int count = 0;
  std::string rname;

  auto two100ms = std::chrono::milliseconds(200);

  while (count++ < (int)(5 * timeoutSec)) {
    auto response = ZMQ_SendReqs(num, SEND_TRP);
    rname = createGetRName(response);
    if (!rname.empty())
      break;

    std::this_thread::sleep_for(two100ms);
  }

  if (rname.empty()) {
    throw InvalidReqException("Timeout for: " + num);
  }

  return rname;
}

int params::getTimeout(const Json::Value &json) const {
  int timeout = json["waitTimeout"].asInt();

  if (timeout <= 0)
    timeout = 2;
  else if (timeout > 10)
    timeout = 10;

  return timeout;
}

[crl-manoj]

@an-tao
any thoughts on this?

[an-tao]

1. you can use the sleepCoro function (in utils/coroutine.h) instead of the blocking sleep metod in standard lib;
2. Change the ZMQ_SendReqs function to a async version;