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Fix for the "next_deadline" bug. #2

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merged 3 commits into from
Aug 23, 2024
Merged

Fix for the "next_deadline" bug. #2

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543308f
Added unit test for the "next_deadline" bug.
serges147 Aug 22, 2024
c9c2fa8
Fix for the "next_deadline" bug.
serges147 Aug 22, 2024
83b2e2c
Fix for the "next_deadline" bug.
serges147 Aug 23, 2024
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35 changes: 22 additions & 13 deletions include/embedded_scheduler/scheduler.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -301,32 +301,41 @@ class EventLoop final
template <typename ExecutionMonitor = std::monostate>
[[nodiscard]] SpinResult<Clock> spin()
{
auto next = time_point::max();
auto now = Clock::now();
auto worst = duration::zero();
SpinResult<Clock> result{.next_deadline = time_point::max(),
.worst_lateness = duration::zero(),
.approx_now = time_point::min()};
if (tree_.empty())
{
result.approx_now = Clock::now();
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In original implementation, we always had 2 consecutive now() calls on the very first loop iteration for the future scheduled event. Now we do only minimum (1) call per iteration.

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Please tag this branch with [[unlikely]]. Maybe there are other places that could use this.

return result;
}

while (auto* const evt = static_cast<EventProxy*>(tree_.min()))
{
next = evt->getDeadline().value(); // The deadline is guaranteed to be set because it is in the tree.
auto lateness = now - next; // Positive if late, zero if on-time.
if (lateness < duration::zero()) // Too early -- either we need to sleep or the time sample is obsolete.
// The deadline is guaranteed to be set because it is in the tree.
const auto deadline = evt->getDeadline().value();
if (result.approx_now < deadline) // Too early -- either we need to sleep or the time sample is obsolete.
{
now = Clock::now(); // The number of calls to Clock::now() is minimized.
lateness = now - next;
if (lateness < duration::zero()) // Nope, even with the latest time sample we are still early -- exit.
result.approx_now = Clock::now(); // The number of calls to Clock::now() is minimized.
if (result.approx_now < deadline) // Nope, even with the latest time sample we are still early -- exit.
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@serges147 serges147 Aug 22, 2024 •
edited
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Note, that I also eliminated subtraction (which is over/under-flow prone strictly speaking). Now I subtract later, when I know for sure that now >= deadline (at line @ 333). Just in case, I will add separate unit test with deadline scheduling time near to timepoint::max - probably it will overflow even now...

{
result.next_deadline = deadline;
break;
}
}
{
ExecutionMonitor monitor{}; // RAII indication of the start and end of the event execution.
// Execution will remove the event from the tree and then possibly re-insert it with a new deadline.
evt->execute({.event = *evt, .deadline = next, .approx_now = now});
evt->execute({.event = *evt, .deadline = deadline, .approx_now = result.approx_now});
(void) monitor;
}
worst = std::max(lateness, worst);
result.next_deadline = time_point::max(); // Reset the next deadline to the maximum possible value.
result.worst_lateness = std::max(result.worst_lateness, result.approx_now - deadline);
}
assert(worst >= duration::zero());
return {.next_deadline = next, .worst_lateness = worst, .approx_now = now};

assert(result.approx_now > time_point::min());
assert(result.worst_lateness >= duration::zero());
return result;
}

/// True if there are no registered events.
Expand Down
68 changes: 63 additions & 5 deletions tests/test_embedded_scheduler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -24,12 +24,16 @@
#include <cstdint>
#include <optional>
#include <ratio>
#include <string>
#include <tuple>
#include <vector>

using testing::Gt;
using testing::Le;
using testing::Ne;
using testing::IsNull;
using testing::NotNull;
using testing::ElementsAre;

// NOLINTBEGIN(bugprone-unchecked-optional-access)
// NOLINTBEGIN(readability-function-cognitive-complexity, misc-const-correctness)
Expand Down Expand Up @@ -90,6 +94,7 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(out.next_deadline, SteadyClockMock::time_point::max());
EXPECT_THAT(out.worst_lateness, SteadyClockMock::duration::zero());
EXPECT_THAT(out.approx_now.time_since_epoch(), 10'000ms);
EXPECT_TRUE(evl->isEmpty());
EXPECT_THAT(evl->getTree()[0U], IsNull());

Expand Down Expand Up @@ -151,6 +156,7 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(out.next_deadline.time_since_epoch(), 10'100ms);
EXPECT_THAT(out.worst_lateness, 0ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 10'000ms);
EXPECT_THAT(evl->getTree().size(), 4);
EXPECT_FALSE(a);
EXPECT_FALSE(b);
Expand All @@ -159,11 +165,12 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)

// Make the first two expire. The one-shot two are still pending.
SteadyClockMock::advance(1100ms);
EXPECT_THAT(11'100ms, SteadyClockMock::now().time_since_epoch());
EXPECT_THAT(SteadyClockMock::now().time_since_epoch(), 11'100ms);
out = evl->spin();
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(out.next_deadline.time_since_epoch(), 11'200ms);
EXPECT_THAT(out.worst_lateness, 1000ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 11'100ms);
EXPECT_THAT(evl->getTree().size(), 4);
EXPECT_TRUE(a);
EXPECT_THAT(a.value().deadline.time_since_epoch(), 11'000ms);
Expand All @@ -182,6 +189,7 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(out.next_deadline.time_since_epoch(), 12'100ms);
EXPECT_THAT(out.worst_lateness, 800ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 12'000ms);
EXPECT_THAT(evl->getTree()[0U]->getDeadline().value().time_since_epoch(), 12'100ms);
EXPECT_THAT(evl->getTree().size(), 2); // C&D have left us.
EXPECT_TRUE(a);
Expand Down Expand Up @@ -214,12 +222,13 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)
EXPECT_THAT(evl->getTree().size(), 1); // Ditto.
out = evl->spin();
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(14'000ms, out.next_deadline.time_since_epoch()); // B removed so the next one is A.
EXPECT_THAT(50ms, out.worst_lateness);
EXPECT_THAT(14'000ms, evl->getTree()[0U]->getDeadline().value().time_since_epoch());
EXPECT_THAT(out.next_deadline.time_since_epoch(), 14'000ms); // B removed so the next one is A.
EXPECT_THAT(out.worst_lateness, 50ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 13'050ms);
EXPECT_THAT(evl->getTree()[0U]->getDeadline().value().time_since_epoch(), 14'000ms);
EXPECT_THAT(1, evl->getTree().size()); // Second dropped.
EXPECT_TRUE(a);
EXPECT_THAT(13'000ms, a.value().deadline.time_since_epoch());
EXPECT_THAT(a.value().deadline.time_since_epoch(), 13'000ms);
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In gtest it is always first actual value, and 2nd-ly the expected - result output (in case of failure) explicitly mentions what was expected and was actually found).

EXPECT_FALSE(b);
EXPECT_FALSE(c);
EXPECT_FALSE(d);
Expand All @@ -230,6 +239,7 @@ TEST(TestEmbeddedScheduler, EventLoopBasic)
// semihost::log(__LINE__, " ", out);
EXPECT_THAT(out.next_deadline.time_since_epoch(), 14'000ms); // Same up.
EXPECT_THAT(out.worst_lateness, 0ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 13'050ms);
EXPECT_FALSE(a);
EXPECT_FALSE(b);
EXPECT_FALSE(c);
Expand Down Expand Up @@ -323,6 +333,54 @@ TEST(TestEmbeddedScheduler, EventLoopPoll)
EXPECT_THAT(evl.getTree()[0U]->getDeadline().value().time_since_epoch(), 210ms); // Skipped ahead!
}

TEST(TestEmbeddedScheduler, EventLoopDefer_single_overdue)
{
using time_point = SteadyClockMock::time_point;
using std::chrono_literals::operator""ms;
SteadyClockMock::reset();
EventLoop<SteadyClockMock> evl;

auto evt = evl.defer(SteadyClockMock::now() + 1000ms, [&](auto) {});
EXPECT_TRUE(evt);

// This is special case - only one deferred event (and no "repeat"-s!), and it is already overdue (by +30ms).
// So, `next_deadline` should be `time_point::max()` b/c there will be nothing left pending after spin.
SteadyClockMock::advance(1000ms + 30ms);
const auto out = evl.spin();
EXPECT_THAT(out.next_deadline.time_since_epoch(), time_point::max().time_since_epoch());
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@serges147 serges147 Aug 22, 2024 •
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At this line @ 350 we've got incorrect next deadline time before the fix (1000ms instead of correct max).

EXPECT_THAT(out.worst_lateness, 30ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 1030ms);
}

TEST(TestEmbeddedScheduler, EventLoopDefer_long_running_callback)
{
using duration = SteadyClockMock::duration;
using std::chrono_literals::operator""ms;
SteadyClockMock::reset();
EventLoop<SteadyClockMock> evl;

std::vector<std::tuple<std::string, duration, duration>> calls;

auto evt_a = evl.defer(SteadyClockMock::now() + 0ms, [&](const auto& arg) { //
// Emulate that it took whole 100ms to execute "a" callback,
// so it will be already overdue for the next "b" event - should be executed as well.
calls.emplace_back("a", arg.deadline.time_since_epoch(), arg.approx_now.time_since_epoch());
SteadyClockMock::advance(100ms);
});
auto evt_b = evl.defer(SteadyClockMock::now() + 20ms, [&](const auto& arg) { //
calls.emplace_back("b", arg.deadline.time_since_epoch(), arg.approx_now.time_since_epoch());
});

const auto out = evl.spin();
EXPECT_THAT(out.next_deadline.time_since_epoch(), duration::max());
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And @ 375 as well.

EXPECT_THAT(out.worst_lateness, 80ms);
EXPECT_THAT(out.approx_now.time_since_epoch(), 100ms);

EXPECT_THAT(calls,
ElementsAre(std::make_tuple("a", 0ms, 0ms), //
std::make_tuple("b", 20ms, 100ms)));
}

TEST(TestEmbeddedScheduler, HandleMovement)
{
using std::chrono_literals::operator""ms;
Expand Down