libstdc++: Add -pthread options to std::future polling test

For linux targets this test doesn't need -lpthread because it only uses
atomics, but for all other targets std::call_once still needs pthreads.
Add the necessary test directives to make that work.

The timings in this test might be too fragile or too target-specific, so
it might need to be adjusted in future, or restricted to only run on
specific targets. For now I've increased the allowed ratio between
wait_for calls before and after the future is made ready, because it was
failing with -O3 -march=native sometimes.

libstdc++-v3/ChangeLog:

	* testsuite/30_threads/future/members/poll.cc: Require gthreads
	and add -pthread for targets that require it. Relax required
	ratio of wait_for calls before/after the future is ready.

1 files changed, 21 insertions, 19 deletions

diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
index 5458057..fff9bea 100644
--- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
+++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
@@ -17,6 +17,8 @@
 
 // { dg-options "-O3" }
 // { dg-do run { target c++11 } }
+// { dg-additional-options "-pthread" { target pthread } }
+// { dg-require-gthreads "" }
 
 #include <future>
 #include <chrono>
@@ -51,31 +53,31 @@ int main()
 
   start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
-    f.wait_until(chrono::system_clock::time_point());
+    f.wait_until(chrono::system_clock::time_point::min());
   stop = chrono::high_resolution_clock::now();
-  double wait_until_sys_epoch __attribute__((unused))
-    = print("wait_until(system_clock epoch)", stop - start);
+  double wait_until_sys_min __attribute__((unused))
+    = print("wait_until(system_clock minimum)", stop - start);
 
   start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
-    f.wait_until(chrono::steady_clock::time_point());
+    f.wait_until(chrono::steady_clock::time_point::min());
   stop = chrono::high_resolution_clock::now();
-  double wait_until_steady_epoch __attribute__((unused))
-    = print("wait_until(steady_clock epoch", stop - start);
+  double wait_until_steady_min __attribute__((unused))
+    = print("wait_until(steady_clock minimum)", stop - start);
 
   start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
-    f.wait_until(chrono::system_clock::time_point::min());
+    f.wait_until(chrono::system_clock::time_point());
   stop = chrono::high_resolution_clock::now();
-  double wait_until_sys_min __attribute__((unused))
-    = print("wait_until(system_clock minimum)", stop - start);
+  double wait_until_sys_epoch __attribute__((unused))
+    = print("wait_until(system_clock epoch)", stop - start);
 
   start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
-    f.wait_until(chrono::steady_clock::time_point::min());
+    f.wait_until(chrono::steady_clock::time_point());
   stop = chrono::high_resolution_clock::now();
-  double wait_until_steady_min __attribute__((unused))
-    = print("wait_until(steady_clock minimum)", stop - start);
+  double wait_until_steady_epoch __attribute__((unused))
+    = print("wait_until(steady_clock epoch", stop - start);
 
   p.set_value(1);
 
@@ -85,19 +87,19 @@ int main()
   stop = chrono::high_resolution_clock::now();
   double ready = print("wait_for when ready", stop - start);
 
-  // polling before ready with wait_for(0s) should be almost as fast as
+  // Polling before ready with wait_for(0s) should be almost as fast as
   // after the result is ready.
-  VERIFY( wait_for_0 < (ready * 10) );
+  VERIFY( wait_for_0 < (ready * 30) );
+
+  // Polling before ready using wait_until(min) should not be terribly slow.
+  VERIFY( wait_until_sys_min < (ready * 100) );
+  VERIFY( wait_until_steady_min < (ready * 100) );
 
   // The following two tests fail with GCC 11, see
   // https://gcc.gnu.org/pipermail/libstdc++/2020-November/051422.html
 #if 0
-  // polling before ready using wait_until(epoch) should not be terribly slow.
+  // Polling before ready using wait_until(epoch) should not be terribly slow.
   VERIFY( wait_until_sys_epoch < (ready * 100) );
   VERIFY( wait_until_steady_epoch < (ready * 100) );
 #endif
-
-  // polling before ready using wait_until(min) should not be terribly slow.
-  VERIFY( wait_until_sys_min < (ready * 100) );
-  VERIFY( wait_until_steady_min < (ready * 100) );
 }