[gcc r13-6464] libstdc++: testsuite: async.cc early timeout

[gcc r13-6464] libstdc++: testsuite: async.cc early timeout

[Alexandre Oliva]

https://gcc.gnu.org/g:16554ba1fe66a09f99adde1220a2cd4f7e5e2d64

commit r13-6464-g16554ba1fe66a09f99adde1220a2cd4f7e5e2d64
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Wed May 4 23:41:38 2022 -0300

    libstdc++: testsuite: async.cc early timeout
    
    The async call and future variable initialization may take a while to
    complete on uniprocessors, especially if the async call and other
    unrelated processes run before context switches back to the main
    thread.
    
    Taking steady_begin only then sometimes causes the 11*100ms in the
    slow clock, counted from before the async call, to not be enough for
    the measured wait to last 1s in the steady clock.  I've seen it fall
    short of 1s by as little as a third of a tenth of a second in some
    cases, but in one surprisingly extreme case the elapsed wait time got
    only up to 216.7ms.
    
    Initializing both timestamps next to each other, before the async
    call, appears to avoid the problem entirely.  I've renamed the
    variable moved out of the block so as to avoid name hiding in the
    subsequent block, that has another steady_begin variable.
    
    The second wait fails a lot less frequently, but the 2s limit has been
    exceeded, so I'm bumping up the max sleep to ~4s, and the tolerance to
    3s.
    
    
    for  libstdc++-v3/ChangeLog
    
            * testsuite/30_threads/async/async.cc (test04): Initialize
            steady_start, renamed from steady_begin, next to slow_start.
            Increase tolerance for final wait.

Diff:
---
 libstdc++-v3/testsuite/30_threads/async/async.cc | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/testsuite/30_threads/async/async.cc b/libstdc++-v3/testsuite/30_threads/async/async.cc
index 2687e92ee40..4e290e581c2 100644
--- a/libstdc++-v3/testsuite/30_threads/async/async.cc
+++ b/libstdc++-v3/testsuite/30_threads/async/async.cc
@@ -20,6 +20,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+#include <iostream>
 
 #include <future>
 #include <thread>
@@ -133,6 +134,7 @@ void test04()
 {
   using namespace std::chrono;
 
+  auto const steady_start = steady_clock::now();
   auto const slow_start = slow_clock::now();
   future<void> f1 = async(launch::async, []() {
       std::this_thread::sleep_for(std::chrono::seconds(2));
@@ -140,21 +142,26 @@ void test04()
 
   // Wait for ~1s
   {
-    auto const steady_begin = steady_clock::now();
     auto const status = f1.wait_until(slow_start + milliseconds(100));
     VERIFY(status == std::future_status::timeout);
-    auto const elapsed = steady_clock::now() - steady_begin;
+    auto const elapsed = steady_clock::now() - steady_start;
+    if (elapsed < seconds(1))
+      std::cout << elapsed.count () << "ns < 1s" << std::endl;
     VERIFY(elapsed >= seconds(1));
     VERIFY(elapsed < seconds(2));
   }
 
-  // Wait for up to ~2s more
+  // Wait for up to ~4s more, but since the async sleep completes, the
+  // actual wait may be shorter than 1s.  Tolerate 3s because 2s
+  // hasn't been enough in some extreme cases.
   {
     auto const steady_begin = steady_clock::now();
-    auto const status = f1.wait_until(slow_start + milliseconds(300));
+    auto const status = f1.wait_until(slow_start + milliseconds(500));
     VERIFY(status == std::future_status::ready);
     auto const elapsed = steady_clock::now() - steady_begin;
-    VERIFY(elapsed < seconds(2));
+    if (elapsed >= seconds(3))
+      std::cout << elapsed.count () << "ns > 2s" << std::endl;
+    VERIFY(elapsed < seconds(3));
   }
 }