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Commit 118a3923 authored by Cameron Pickett's avatar Cameron Pickett Committed by Facebook GitHub Bot
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Do not swallow child exceptions on cancellation 

Summary:
Aligns `collectAll` and `collectAny` behaviour and simplifies the logic for propagating child exceptions on cancellation.

Prior to this change, we were conditionally setting `firstException` dependent on whether cancellation was requested or not. Additionally, `collectAny` was unconditionally returning `co_cancelled` even if all the child tasks completed successfully.

Now, the behaviour is consistent between general errors and cancellation: If any child task completes in error (including folly::OperationCancelled), then the parent `collectAll`/`collectAny` will propagate that failure. Otherwise, if no child fails, then `collectAll`/`collectAny` will propagate that success.

(Note: this ignores all push blocking failures!)

Reviewed By: iahs

Differential Revision: D31266586

fbshipit-source-id: b6eba6ab2a0a3634b112318b1810819d7916acdb
parent ff7c3177
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Showing with 56 additions and 114 deletions
folly/experimental/coro/Collect-inl.h
View file @ 118a3923
......@@ -135,7 +135,6 @@ auto collectAllImpl(
CancellationToken::merge(parentCancelToken, cancelSource.getToken());
exception_wrapper firstException;
std::atomic<bool> anyFailures{false};
auto makeTask = [&](auto&& awaitable, auto& result) -> BarrierTask {
using await_result = semi_await_result_t<decltype(awaitable)>;
......@@ -153,9 +152,7 @@ auto collectAllImpl(
cancelToken, static_cast<decltype(awaitable)>(awaitable))));
}
} catch (...) {
anyFailures.store(true, std::memory_order_relaxed);
if (!cancelSource.requestCancellation() &&
!parentCancelToken.isCancellationRequested()) {
if (!cancelSource.requestCancellation()) {
// This was the first failure, remember its error.
firstException = exception_wrapper{std::current_exception()};
}
......@@ -194,17 +191,10 @@ auto collectAllImpl(
// the use of co_viaIfAsync() within makeBarrierTask().
co_await UnsafeResumeInlineSemiAwaitable{barrier.arriveAndWait()};
if (anyFailures.load(std::memory_order_relaxed)) {
if (firstException) {
co_yield co_error(std::move(firstException));
}
// Parent task was cancelled before any child tasks failed.
// Complete with the OperationCancelled error instead of the
// child task's errors.
co_yield co_cancelled;
}
co_return std::tuple<collect_all_component_t<SemiAwaitables>...>{
getValueOrUnit(std::get<Indices>(std::move(results)))...};
}
......@@ -311,10 +301,6 @@ auto collectAnyImpl(
}
}))...);
if (parentCancelToken.isCancellationRequested()) {
co_yield co_cancelled;
}
co_return firstCompletion;
}
......@@ -377,7 +363,6 @@ auto collectAllRange(InputRange awaitables)
tryResults;
exception_wrapper firstException;
std::atomic<bool> anyFailures = false;
using awaitable_type = remove_cvref_t<detail::range_reference_t<InputRange>>;
auto makeTask = [&](awaitable_type semiAwaitable,
......@@ -389,7 +374,6 @@ auto collectAllRange(InputRange awaitables)
executor.get_alias(),
co_withCancellation(cancelToken, std::move(semiAwaitable))));
} catch (...) {
anyFailures.store(true, std::memory_order_relaxed);
if (!cancelSource.requestCancellation()) {
firstException = exception_wrapper{std::current_exception()};
}
......@@ -429,16 +413,10 @@ auto collectAllRange(InputRange awaitables)
}
// Check if there were any exceptions and rethrow the first one.
if (anyFailures.load(std::memory_order_relaxed)) {
if (firstException) {
co_yield co_error(std::move(firstException));
}
// Cancellation was requested of the parent Task before any of the
// child tasks failed.
co_yield co_cancelled;
}
std::vector<detail::collect_all_range_component_t<
detail::range_reference_t<InputRange>>>
results;
......@@ -463,7 +441,6 @@ auto collectAllRange(InputRange awaitables) -> folly::coro::Task<void> {
co_await co_current_cancellation_token, cancelSource.getToken());
exception_wrapper firstException;
std::atomic<bool> anyFailures = false;
using awaitable_type = remove_cvref_t<detail::range_reference_t<InputRange>>;
auto makeTask = [&](awaitable_type semiAwaitable) -> detail::BarrierTask {
......@@ -472,7 +449,6 @@ auto collectAllRange(InputRange awaitables) -> folly::coro::Task<void> {
executor.get_alias(),
co_withCancellation(cancelToken, std::move(semiAwaitable)));
} catch (...) {
anyFailures.store(true, std::memory_order_relaxed);
if (!cancelSource.requestCancellation()) {
firstException = exception_wrapper{std::current_exception()};
}
......@@ -509,11 +485,9 @@ auto collectAllRange(InputRange awaitables) -> folly::coro::Task<void> {
}
// Check if there were any exceptions and rethrow the first one.
if (anyFailures.load(std::memory_order_relaxed)) {
if (firstException) {
co_yield co_error(std::move(firstException));
}
}
}
template <typename InputRange>
......@@ -607,10 +581,8 @@ auto collectAllWindowed(InputRange awaitables, std::size_t maxConcurrency)
co_await co_current_cancellation_token, cancelSource.getToken());
exception_wrapper firstException;
std::atomic<bool> anyFailures = false;
const auto trySetFirstException = [&](exception_wrapper&& e) noexcept {
anyFailures.store(true, std::memory_order_relaxed);
if (!cancelSource.requestCancellation()) {
// This is first entity to request cancellation.
firstException = std::move(e);
......@@ -700,14 +672,8 @@ auto collectAllWindowed(InputRange awaitables, std::size_t maxConcurrency)
co_await detail::UnsafeResumeInlineSemiAwaitable{barrier.arriveAndWait()};
if (iterationException) {
co_yield co_error(std::move(iterationException));
} else if (anyFailures.load(std::memory_order_relaxed)) {
if (firstException) {
co_yield co_error(std::move(firstException));
}
co_yield co_cancelled;
if (auto& ex = iterationException ? iterationException : firstException) {
co_yield co_error(std::move(ex));
}
}
......@@ -731,12 +697,9 @@ auto collectAllWindowed(InputRange awaitables, std::size_t maxConcurrency)
CancellationToken::merge(parentCancelToken, cancelSource.getToken());
exception_wrapper firstException;
std::atomic<bool> anyFailures = false;
auto trySetFirstException = [&](exception_wrapper&& e) noexcept {
anyFailures.store(true, std::memory_order_relaxed);
if (!cancelSource.requestCancellation() &&
!parentCancelToken.isCancellationRequested()) {
if (!cancelSource.requestCancellation()) {
// This is first entity to request cancellation.
firstException = std::move(e);
}
......@@ -846,16 +809,8 @@ auto collectAllWindowed(InputRange awaitables, std::size_t maxConcurrency)
co_await detail::UnsafeResumeInlineSemiAwaitable{barrier.arriveAndWait()};
if (iterationException) {
co_yield co_error(std::move(iterationException));
} else if (anyFailures.load(std::memory_order_relaxed)) {
if (firstException) {
co_yield co_error(std::move(firstException));
}
// Otherwise, cancellation was requested before any of the child tasks
// failed so complete with the OperationCancelled error.
co_yield co_cancelled;
if (auto& ex = iterationException ? iterationException : firstException) {
co_yield co_error(std::move(ex));
}
std::vector<detail::collect_all_range_component_t<
......@@ -1100,10 +1055,6 @@ auto collectAnyRange(InputRange awaitables) -> folly::coro::Task<std::pair<
co_await folly::coro::co_withCancellation(
cancelToken, folly::coro::collectAllRange(tasks | ranges::views::move));
if (parentCancelToken.isCancellationRequested()) {
co_yield co_cancelled;
}
co_return firstCompletion;
}
......
folly/experimental/coro/test/CollectTest.cpp
View file @ 118a3923
......@@ -2039,7 +2039,6 @@ TEST_F(CollectAnyTest, CollectAnyCancelsSubtasksWhenParentTaskCancelled) {
folly::coro::blockingWait([]() -> folly::coro::Task<void> {
auto start = std::chrono::steady_clock::now();
folly::CancellationSource cancelSource;
try {
auto [index, result] = co_await folly::coro::co_withCancellation(
cancelSource.getToken(),
folly::coro::collectAny(
......@@ -2059,11 +2058,8 @@ TEST_F(CollectAnyTest, CollectAnyCancelsSubtasksWhenParentTaskCancelled) {
co_await sleepThatShouldBeCancelled(15s);
co_return 123;
}()));
ADD_FAILURE() << "Hit unexpected codepath";
} catch (const folly::OperationCancelled&) {
auto end = std::chrono::steady_clock::now();
EXPECT_LT(end - start, 1s);
}
}());
}
......@@ -2530,7 +2526,6 @@ TEST_F(CollectAnyRangeTest, CollectAnyCancelsSubtasksWhenParentTaskCancelled) {
folly::coro::blockingWait([]() -> folly::coro::Task<void> {
auto start = std::chrono::steady_clock::now();
folly::CancellationSource cancelSource;
try {
auto generateTasks =
[&]() -> folly::coro::Generator<folly::coro::Task<int>&&> {
co_yield [&]() -> folly::coro::Task<int> {
......@@ -2551,13 +2546,9 @@ TEST_F(CollectAnyRangeTest, CollectAnyCancelsSubtasksWhenParentTaskCancelled) {
}();
};
auto [index, result] = co_await folly::coro::co_withCancellation(
cancelSource.getToken(),
folly::coro::collectAnyRange(generateTasks()));
ADD_FAILURE() << "Hit unexpected codepath";
} catch (const folly::OperationCancelled&) {
cancelSource.getToken(), folly::coro::collectAnyRange(generateTasks()));
auto end = std::chrono::steady_clock::now();
EXPECT_LT(end - start, 1s);
}
}());
}
......
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