[fiber] Guarantee minimum for durations < 1µs

src/modm/processing/fiber/functions.hpp

@@ -90,12 +90,16 @@ poll_for(std::chrono::duration<Rep, Period> sleep_duration, Function &&condition
 							  std::chrono::duration<Rep, std::milli>>,
 		modm::chrono::milli_clock, modm::chrono::micro_clock>;
 
+	// Ensure the sleep duration is rounded up to the next full clock tick
+	const auto clock_sleep_duration(
+			std::chrono::ceil<typename Clock::duration>(sleep_duration));
+
 	const auto start = Clock::now();
 	do {
 		modm::this_fiber::yield();
 		if (std::forward<Function>(condition)()) return true;
 	}
-	while((Clock::now() - start) <= sleep_duration);
+	while((Clock::now() - start) < clock_sleep_duration);
 	return false;
 }
 
@@ -125,7 +129,7 @@ poll_until(std::chrono::time_point<Clock, Duration> sleep_time, Function &&condi
 		modm::this_fiber::yield();
 		if (std::forward<Function>(condition)()) return true;
 	}
-	while((Clock::now() - start) <= sleep_duration);
+	while((Clock::now() - start) < sleep_duration);
 	return false;
 }
 

test/modm/processing/fiber/fiber_test.cpp

@@ -16,7 +16,8 @@
 #include <modm-test/mock/clock.hpp>
 
 using namespace std::chrono_literals;
-using test_clock = modm_test::chrono::milli_clock;
+using test_clock_ms = modm_test::chrono::milli_clock;
+using test_clock_us = modm_test::chrono::micro_clock;
 
 void
 FiberTest::setUp()
@@ -103,7 +104,7 @@ FiberTest::testYieldFromSubroutine()
 void
 FiberTest::testPollFor()
 {
-	test_clock::setTime(1251);
+	test_clock_ms::setTime(1251);
 	TEST_ASSERT_TRUE(modm::this_fiber::poll_for(20ms, []{ return true; }));
 	// timeout is tested in the SleepFor() test
 }
@@ -112,7 +113,7 @@ FiberTest::testPollFor()
 void
 FiberTest::testPollUntil()
 {
-	test_clock::setTime(451250);
+	test_clock_ms::setTime(451250);
 	TEST_ASSERT_TRUE(modm::this_fiber::poll_until(modm::Clock::now() + 20ms, []{ return true; }));
 	TEST_ASSERT_TRUE(modm::this_fiber::poll_until(modm::Clock::now() - 20ms, []{ return true; }));
 	// timeout is tested in the SleepUntil() tests
@@ -123,33 +124,52 @@ static void
 f4()
 {
 	TEST_ASSERT_EQUALS(state++, 0u);
-	modm::this_fiber::sleep_for(50ms); // goto 1
+	// yields only once
+	modm::this_fiber::sleep_for(0s); // goto 1
+
+	TEST_ASSERT_EQUALS(state++, 2u);
+	// rounds up to 1us, not 0us!
+	modm::this_fiber::sleep_for(100ns); // goto 3
+
 	TEST_ASSERT_EQUALS(state++, 5u);
+	modm::this_fiber::sleep_for(50ms); // goto 6
+	TEST_ASSERT_EQUALS(state++, 10u);
 }
 
 static void
 f5()
 {
 	TEST_ASSERT_EQUALS(state++, 1u);
-	test_clock::increment(10);
-	TEST_ASSERT_EQUALS(state++, 2u);
-	modm::this_fiber::yield();
+	modm::this_fiber::yield(); // goto 2
 
-	test_clock::increment(20);
 	TEST_ASSERT_EQUALS(state++, 3u);
 	modm::this_fiber::yield();
 
-	test_clock::increment(30);
 	TEST_ASSERT_EQUALS(state++, 4u);
+	test_clock_us::increment(1);
 	modm::this_fiber::yield(); // goto 5
 
 	TEST_ASSERT_EQUALS(state++, 6u);
+	test_clock_ms::increment(10);
+	TEST_ASSERT_EQUALS(state++, 7u);
+	modm::this_fiber::yield();
+
+	test_clock_ms::increment(20);
+	TEST_ASSERT_EQUALS(state++, 8u);
+	modm::this_fiber::yield();
+
+	test_clock_ms::increment(30);
+	TEST_ASSERT_EQUALS(state++, 9u);
+	modm::this_fiber::yield(); // goto 10
+
+	TEST_ASSERT_EQUALS(state++, 11u);
 }
 
 static void
 runSleepFor(uint32_t startTime)
 {
-	test_clock::setTime(startTime);
+	test_clock_ms::setTime(startTime);
+	test_clock_us::setTime(startTime);
 	modm::fiber::Task fiber1(stack1, f4), fiber2(stack2, f5);
 	modm::fiber::Scheduler::run();
 }
@@ -165,6 +185,25 @@ FiberTest::testSleepFor()
 
 static void
 f6()
+{
+	TEST_ASSERT_EQUALS(state++, 1u);
+	test_clock_ms::increment(10);
+	TEST_ASSERT_EQUALS(state++, 2u);
+	modm::this_fiber::yield();
+
+	test_clock_ms::increment(20);
+	TEST_ASSERT_EQUALS(state++, 3u);
+	modm::this_fiber::yield();
+
+	test_clock_ms::increment(30);
+	TEST_ASSERT_EQUALS(state++, 4u);
+	modm::this_fiber::yield(); // goto 5
+
+	TEST_ASSERT_EQUALS(state++, 6u);
+}
+
+static void
+f7()
 {
 	TEST_ASSERT_EQUALS(state++, 0u); // goto 1
 	modm::this_fiber::sleep_until(modm::Clock::now() + 50ms);
@@ -177,8 +216,8 @@ f6()
 static void
 runSleepUntil(uint32_t startTime)
 {
-	test_clock::setTime(startTime);
-	modm::fiber::Task fiber1(stack1, f6), fiber2(stack2, f5);
+	test_clock_ms::setTime(startTime);
+	modm::fiber::Task fiber1(stack1, f7), fiber2(stack2, f6);
 	modm::fiber::Scheduler::run();
 }
 
@@ -191,7 +230,7 @@ FiberTest::testSleepUntil()
 }
 
 static void
-f7(modm::fiber::stop_token stoken)
+f8(modm::fiber::stop_token stoken)
 {
 	TEST_ASSERT_EQUALS(state++, 0u);
 	TEST_ASSERT_TRUE(stoken.stop_possible());
@@ -208,7 +247,7 @@ f7(modm::fiber::stop_token stoken)
 void
 FiberTest::testStopToken()
 {
-	modm::fiber::Task fiber1(stack1, f7);
+	modm::fiber::Task fiber1(stack1, f8);
 	modm::fiber::Task fiber2(stack2, [&](modm::fiber::stop_token stoken)
 	{
 		TEST_ASSERT_EQUALS(state++, 1u);