From 5dfcf5911c8b0879ab98dd5398c12a9f3933e52f Mon Sep 17 00:00:00 2001
From: BlackMATov <blackmatov@gmail.com>
Date: Mon, 17 Dec 2018 13:03:17 +0700
Subject: [PATCH] scheduler: process_one_task

---
 jobber.hpp          |  2 +-
 promise_tests.cpp   |  2 +-
 scheduler.hpp       | 11 +++++++++++
 scheduler_tests.cpp | 16 ++++++++++++++++
 4 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/jobber.hpp b/jobber.hpp
index 032f64f..db4341e 100644
--- a/jobber.hpp
+++ b/jobber.hpp
@@ -277,7 +277,7 @@ namespace jobber_hpp
         tasks_.emplace_back(priority, std::move(task));
         std::push_heap(tasks_.begin(), tasks_.end());
         ++active_task_count_;
-        cond_var_.notify_all();
+        cond_var_.notify_one();
     }
 
     inline jobber::task_ptr jobber::pop_task_() noexcept {
diff --git a/promise_tests.cpp b/promise_tests.cpp
index 51eff9a..c9762d2 100644
--- a/promise_tests.cpp
+++ b/promise_tests.cpp
@@ -1039,7 +1039,7 @@ TEST_CASE("promise") {
                     pr::make_rejected_promise<float>(std::logic_error("hello fail")));
             }).except([&call_fail_with_logic_error](std::exception_ptr e){
                 call_fail_with_logic_error = check_hello_fail_exception(e);
-                return 0;
+                return std::make_tuple(0, 0.f);
             });
             REQUIRE(call_fail_with_logic_error);
         }
diff --git a/scheduler.hpp b/scheduler.hpp
index 97af654..309a7c9 100644
--- a/scheduler.hpp
+++ b/scheduler.hpp
@@ -65,6 +65,7 @@ namespace scheduler_hpp
                  , typename R = schedule_invoke_result_t<F, Args...> >
         promise<R> schedule(scheduler_priority scheduler_priority, F&& f, Args&&... args);
 
+        bool process_one_task() noexcept;
         scheduler_wait_status process_all_tasks() noexcept;
 
         template < typename Rep, typename Period >
@@ -157,6 +158,15 @@ namespace scheduler_hpp
         return future;
     }
 
+    inline bool scheduler::process_one_task() noexcept {
+        std::unique_lock<std::mutex> lock(tasks_mutex_);
+        if ( tasks_.empty() ) {
+            return false;
+        }
+        process_task_(std::move(lock));
+        return true;
+    }
+
     inline scheduler_wait_status scheduler::process_all_tasks() noexcept {
         while ( !cancelled_ && active_task_count_ ) {
             std::unique_lock<std::mutex> lock(tasks_mutex_);
@@ -237,6 +247,7 @@ namespace scheduler_hpp
         if ( task ) {
             lock.unlock();
             task->run();
+            lock.lock();
             --active_task_count_;
             cond_var_.notify_all();
         }
diff --git a/scheduler_tests.cpp b/scheduler_tests.cpp
index f092eb9..b2065ad 100644
--- a/scheduler_tests.cpp
+++ b/scheduler_tests.cpp
@@ -46,6 +46,22 @@ TEST_CASE("scheduler") {
         s.process_all_tasks();
         REQUIRE(counter == 3);
     }
+    {
+        sd::scheduler s;
+        int counter = 0;
+        s.schedule([&counter](){ ++counter; });
+        s.schedule([&counter](){ ++counter; });
+        s.schedule([&counter](){ ++counter; });
+        REQUIRE(counter == 0);
+        REQUIRE(s.process_one_task());
+        REQUIRE(counter == 1);
+        REQUIRE(s.process_one_task());
+        REQUIRE(counter == 2);
+        REQUIRE(s.process_one_task());
+        REQUIRE(counter == 3);
+        REQUIRE_FALSE(s.process_one_task());
+        REQUIRE(counter == 3);
+    }
     {
         sd::scheduler s;
         int counter = 0;