cross-tree: convert deprecated later() to yield()

A recent patch deprecated the later() function, splitting its work to
yield() and check_for_io_immediately(). The result was numerous
deprecation warnings when building Seastar and its tests, so this patch
sets out replace every call to later() by yield() - because as far as I
can tell, non of the callers of later() needed check_for_io_immediately().

While doing this, I noticed that some of the code using later() (and now
yield()) were missing an explicit include of <seastar/util/later.hh>.
This is something we'll probably regret later, so I took the opportunity
to also add the missing include.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20220110160202.573719-1-nyh@scylladb.com>

src/core/file.cc

@@ -775,8 +775,8 @@ append_challenged_posix_file_impl::commit_size(uint64_t size) noexcept {
 future<size_t>
 append_challenged_posix_file_impl::read_dma(uint64_t pos, void* buffer, size_t len, const io_priority_class& pc, io_intent* intent) noexcept {
     if (pos >= _logical_size) {
-        // later() avoids tail recursion
-        return later().then([] {
+        // yield() avoids tail recursion
+        return yield().then([] {
             return size_t(0);
         });
     }
@@ -795,8 +795,8 @@ append_challenged_posix_file_impl::read_dma(uint64_t pos, void* buffer, size_t l
 future<size_t>
 append_challenged_posix_file_impl::read_dma(uint64_t pos, std::vector<iovec> iov, const io_priority_class& pc, io_intent* intent) noexcept {
     if (pos >= _logical_size) {
-        // later() avoids tail recursion
-        return later().then([] {
+        // yield() avoids tail recursion
+        return yield().then([] {
             return size_t(0);
         });
     }

tests/perf/future_util_perf.cc

@@ -64,7 +64,7 @@ PERF_TEST_F(parallel_for_each, immediate)
 future<> suspend(int v, int& vs)
 {
     vs += v;
-    return later();
+    return yield();
 }
 
 PERF_TEST_F(parallel_for_each, suspend)

tests/perf/perf_tests.cc

@@ -222,7 +222,7 @@ void performance_test::do_run(const config& conf)
     // dry run, estimate the number of iterations
     if (conf.single_run_duration.count()) {
         // switch out of seastar thread
-        later().then([&] {
+        yield().then([&] {
             tmr.arm(conf.single_run_duration);
             return do_single_run().finally([&] {
                 tmr.cancel();
@@ -235,7 +235,7 @@ void performance_test::do_run(const config& conf)
     uint64_t total_iterations = 0;
     for (auto i = 0u; i < conf.number_of_runs; i++) {
         // switch out of seastar thread
-        later().then([&] {
+        yield().then([&] {
             _single_run_iterations = 0;
             return do_single_run().then([&] (clock_type::duration dt) {
                 double ns = std::chrono::duration_cast<std::chrono::nanoseconds>(dt).count();

tests/unit/coroutines_test.cc

@@ -22,6 +22,7 @@
 #include <seastar/core/future-util.hh>
 #include <seastar/testing/test_case.hh>
 #include <seastar/core/sleep.hh>
+#include <seastar/util/later.hh>
 
 using namespace seastar;
 using namespace std::chrono_literals;
@@ -41,13 +42,13 @@ SEASTAR_TEST_CASE(test_coroutines_not_compiled_in) {
 namespace {
 
 future<int> old_fashioned_continuations() {
-    return later().then([] {
+    return yield().then([] {
         return 42;
     });
 }
 
 future<int> simple_coroutine() {
-    co_await later();
+    co_await yield();
     co_return 53;
 }
 
@@ -60,7 +61,7 @@ future<std::tuple<int, double>> tuple_coroutine() {
 }
 
 future<int> failing_coroutine() {
-    co_await later();
+    co_await yield();
     throw 42;
 }
 
@@ -69,7 +70,7 @@ future<int> failing_coroutine() {
 }
 
 future<int> failing_coroutine2() noexcept {
-    co_await later();
+    co_await yield();
     co_return throw_exception(17);
 }
 
@@ -157,7 +158,7 @@ SEASTAR_TEST_CASE(test_scheduling_group) {
 SEASTAR_TEST_CASE(test_preemption) {
     bool x = false;
     unsigned preempted = 0;
-    auto f = later().then([&x] {
+    auto f = yield().then([&x] {
             x = true;
         });
 
@@ -169,7 +170,7 @@ SEASTAR_TEST_CASE(test_preemption) {
         co_await make_ready_future<>();
     }
     auto save_x = x;
-    // wait for later() to complete
+    // wait for yield() to complete
     co_await std::move(f);
     BOOST_REQUIRE(save_x);
     co_return;

tests/unit/expiring_fifo_test.cc

@@ -93,7 +93,7 @@ SEASTAR_TEST_CASE(test_expiry_operations) {
         BOOST_REQUIRE_EQUAL(fifo.front(), 1);
 
         manual_clock::advance(1s);
-        later().get();
+        yield().get();
 
         BOOST_REQUIRE(fifo.empty());
         BOOST_REQUIRE_EQUAL(fifo.size(), 0u);
@@ -108,7 +108,7 @@ SEASTAR_TEST_CASE(test_expiry_operations) {
         fifo.push_back(3);
 
         manual_clock::advance(1s);
-        later().get();
+        yield().get();
 
         BOOST_REQUIRE(!fifo.empty());
         BOOST_REQUIRE_EQUAL(fifo.size(), 2u);
@@ -130,7 +130,7 @@ SEASTAR_TEST_CASE(test_expiry_operations) {
         fifo.push_back(4, manual_clock::now() + 2s);
 
         manual_clock::advance(1s);
-        later().get();
+        yield().get();
 
         BOOST_REQUIRE(!fifo.empty());
         BOOST_REQUIRE_EQUAL(fifo.size(), 2u);
@@ -154,7 +154,7 @@ SEASTAR_TEST_CASE(test_expiry_operations) {
         fifo.push_back(4, manual_clock::now() + 1s);
 
         manual_clock::advance(1s);
-        later().get();
+        yield().get();
 
         BOOST_REQUIRE(!fifo.empty());
         BOOST_REQUIRE_EQUAL(fifo.size(), 1u);
@@ -177,7 +177,7 @@ SEASTAR_TEST_CASE(test_expiry_operations) {
         fifo.push_back(5);
 
         manual_clock::advance(1s);
-        later().get();
+        yield().get();
 
         BOOST_REQUIRE_EQUAL(fifo.size(), 2u);
         BOOST_REQUIRE_EQUAL(fifo.front(), 1);

tests/unit/fair_queue_test.cc

@@ -192,7 +192,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_equal_2classes) {
         env.do_op(b, 1);
     }
 
-    later().get();
+    yield().get();
     // allow half the requests in
     env.tick(100);
     env.verify("equal_2classes", {1, 1});
@@ -213,7 +213,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_equal_4classes) {
         env.do_op(c, 1);
         env.do_op(d, 1);
     }
-    later().get();
+    yield().get();
     // allow half the requests in
     env.tick(200);
     env.verify("equal_4classes", {1, 1, 1, 1});
@@ -230,7 +230,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_different_shares) {
         env.do_op(a, 1);
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
     // allow half the requests in
     env.tick(100);
     return env.verify("different_shares", {1, 2});
@@ -250,7 +250,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_equal_hi_capacity_2classes) {
         env.do_op(a, 1);
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
 
     // queue has capacity 10, 10 x 10 = 100, allow half the requests in
     env.tick(10);
@@ -272,7 +272,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_different_shares_hi_capacity) {
         env.do_op(a, 1);
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
     // queue has capacity 10, 10 x 10 = 100, allow half the requests in
     env.tick(10);
     env.verify("different_shares_hi_capacity", {1, 2});
@@ -289,7 +289,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_different_weights) {
         env.do_op(a, 2);
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
     // allow half the requests in
     env.tick(100);
     env.verify("different_weights", {1, 2});
@@ -305,7 +305,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_dominant_queue) {
     for (int i = 0; i < 100; ++i) {
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
 
     // consume all requests
     env.tick(100);
@@ -335,7 +335,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_forgiving_queue) {
     for (int i = 0; i < 100; ++i) {
         env.do_op(a, 1);
     }
-    later().get();
+    yield().get();
 
     // consume all requests
     env.tick(100);
@@ -345,7 +345,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_forgiving_queue) {
         env.do_op(a, 1);
         env.do_op(b, 1);
     }
-    later().get();
+    yield().get();
 
     // allow half the requests in
     env.tick(100);
@@ -366,13 +366,13 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_update_shares) {
         env.do_op(b, 1);
     }
 
-    later().get();
+    yield().get();
     // allow 25% of the requests in
     env.tick(250);
     env.update_shares(a, 10);
     env.update_shares(b, 20);
 
-    later().get();
+    yield().get();
     // allow 25% of the requests in
     env.tick(250);
     env.verify("update_shares", {1, 1}, 2);
@@ -441,7 +441,7 @@ SEASTAR_THREAD_TEST_CASE(test_fair_queue_random_run) {
         env.do_op(b, 1);
     }
 
-    later().get();
+    yield().get();
     // In total allow half the requests in
     env.tick(reqs);