Re: [committed] libstdc++: Fix __thread_yield for non-gthreads targets

[Jonathan Wakely via Gcc-patches]

On 15/02/21 16:13 +0000, Jonathan Wakely wrote:

The __gthread_yield() function is only defined for gthreads targets, so
check _GLIBCXX_HAS_GTHREADS before using it.

Also reorder __thread_relax and __thread_yield so that the former can
use the latter instead of repeating the same preprocessor checks.

libstdc++-v3/ChangeLog:

        * include/bits/atomic_wait.h (__thread_yield()): Check
        _GLIBCXX_HAS_GTHREADS before using __gthread_yield.
        (__thread_relax()): Use __thread_yield() instead of repeating
        the preprocessor checks for __gthread_yield.

--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -213,24 +213,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
      { _M_w._M_do_wait(_M_version); }
    };

-    inline void
-    __thread_relax() noexcept
-    {
-#if defined __i386__ || defined __x86_64__
-      __builtin_ia32_pause();
-#elif defined _GLIBCXX_USE_SCHED_YIELD
-      __gthread_yield();
-#endif
-    }
-
    inline void
    __thread_yield() noexcept
    {
-#if defined _GLIBCXX_USE_SCHED_YIELD
+#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
     __gthread_yield();
#endif
    }

+    inline void
+    __thread_relax() noexcept
+    {
+#if defined __i386__ || defined __x86_64__
+      __builtin_ia32_pause();
+#else
+      __gthread_yield();

As I said in the ChangeLog, this was supposed to be changed from
__gthread_yield to __thread_yield. Fixed by this patch.

Tested powerpc64le-linux. Committed to trunk.


commit 9d449189ee4304ce4f250351c8aa393324421eef
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Feb 19 09:54:04 2021

    libstdc++: Fix __thread_relax for non-gthreads non-x86 targets
    
    My recent change to the preprocessor conditions in __thread_relax() was
    supposed to also change the __gthread_yield() call to __thread_yield(),
    which has the right preprocessor checks. Instead I just removed the
    check for _GLIBCXX_USE_SCHED_YIELD which means the __gthread_yield()
    call will be ill-formed for non-gthreads targets, and targets without
    sched_yield(). This fixes it properly.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/atomic_wait.h (__thread_relax()): Call
            __thread_yield() not __gthread_yield().

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 37085ae8e50..424fccbe4c5 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -217,7 +217,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __thread_yield() noexcept
     {
 #if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
-     __gthread_yield();
+      __gthread_yield();
 #endif
     }
 
@@ -227,7 +227,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if defined __i386__ || defined __x86_64__
       __builtin_ia32_pause();
 #else
-      __gthread_yield();
+      __thread_yield();
 #endif
     }
   } // namespace __detail