Re: [PATCH] libstdc++: Allow emergency EH alloc pool size to be tuned [PR68606]

[Jonathan Wakely <jwakely@redhat.com>]

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On Tue, 11 Oct 2022 at 19:58, Jonathan Wakely wrote:
>
>
>
> On Tue, 11 Oct 2022, 19:38 David Edelsohn via Libstdc++, <libstdc++@gcc.gnu.org> wrote:
>>
>> This patch seems to have broken bootstrap on AIX.  It seems to assume
>> methods that aren't guaranteed to be defined.
>
>
>
> It doesn't use anything that wasn't already used by that file.
>
> I have no idea how it ever compiled if it doesn't now, but I'll take a look.

The problem was inconsistent namespace qualification. The
__scoped_lock type is always present on AIX even for the
single-threaded multilib, but the code wasn't referring to the correct
__scoped_lock type consistently.

Fixed like so. Bootstrapped on x86_64-linux with --disable-threads
(I'm still waiting for the AIX build, but the symptom and cure are the
same as for --disable-threads on other targets).

Pushed to trunk.

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commit 23c3cbaed36f6d2f3a7a64f6ebda69329723514b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Oct 11 20:19:08 2022

    libstdc++: Fix bootstrap for --disable-threads build [PR107221]
    
    The __scoped_lock type should be used unqualified so that we always
    refer to pool::__scoped_lock, which might be the dummy fallback
    implementation.
    
    The __mutex and __scoped_lock types in <ext/concurrence.h> already work
    fine without __GTHREADS being defined, but that header isn't included at
    all unless _GLIBCXX_HOSTED != 0. The fallback implementation should be
    used for ! _GLIBCXX_HOSTED instead of for !defined __GTHREADS.
    
    libstdc++-v3/ChangeLog:
    
            PR bootstrap/107221
            * libsupc++/eh_alloc.cc (pool): Change preprocessor condition
            for using __mutex from __GTHREADS to _GLIBCXX_HOSTED.
            (pool::allocate): Remove namespace qualification to use
            pool::__scoped_lock instead of __gnu_cxx::__scoped_lock.

diff --git a/libstdc++-v3/libsupc++/eh_alloc.cc b/libstdc++-v3/libsupc++/eh_alloc.cc
index 50dc37c0d9c..81b8a1548c6 100644
--- a/libstdc++-v3/libsupc++/eh_alloc.cc
+++ b/libstdc++-v3/libsupc++/eh_alloc.cc
@@ -145,7 +145,7 @@ namespace
 	char data[] __attribute__((aligned));
       };
 
-#ifdef __GTHREADS
+#if _GLIBCXX_HOSTED
       // A single mutex controlling emergency allocations.
       __gnu_cxx::__mutex emergency_mutex;
       using __scoped_lock = __gnu_cxx::__scoped_lock;
@@ -236,7 +236,7 @@ namespace
 
   void *pool::allocate (std::size_t size) noexcept
     {
-      __gnu_cxx::__scoped_lock sentry(emergency_mutex);
+      __scoped_lock sentry(emergency_mutex);
       // We need an additional size_t member plus the padding to
       // ensure proper alignment of data.
       size += offsetof (allocated_entry, data);