From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 5 Jan 2023 20:23:26 +0000 (+0000)
Subject: libstdc++: Use lock-free type for __platform_wait_t
X-Git-Tag: basepoints/gcc-14~2088
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=dc22cf461278ace754042d9388a62afb002dfa0e;p=thirdparty%2Fgcc.git

libstdc++: Use lock-free type for __platform_wait_t

For non-futex targets the __platform_wait_t type is currently uint64_t,
but that requires a lock in libatomic for some 32-bit targets. We don't
really need a 64-bit type, so use unsigned long if that is lock-free,
and int otherwise. This should mean it's lock-free on a wider set of
targets.

libstdc++-v3/ChangeLog:

	* include/bits/atomic_wait.h (__detail::__platform_wait_t):
	Define as unsigned long if always lock-free, and unsigned int
	otherwise.
---

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index bd1ed56d1576..1d7a034a1658 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 // and __platform_notify() if there is a more efficient primitive supported
 // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than
 // a mutex/condvar based wait.
-    using __platform_wait_t = uint64_t;
+# if ATOMIC_LONG_LOCK_FREE == 2
+    using __platform_wait_t = unsigned long;
+# else
+    using __platform_wait_t = unsigned int;
+# endif
     inline constexpr size_t __platform_wait_alignment
       = __alignof__(__platform_wait_t);
 #endif