From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 8EB6C3856DDA for ; Wed, 13 Sep 2023 12:32:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 8EB6C3856DDA Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694608349; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=wHXRqgZKDIrrWkXKrorMc/r4f8VnKNDaMiuy07S5U3I=; b=P/JDSSRy27LTV/VBrkXpxYighQC78t+TCQxTf4PRpmw2I4r4pNEXkRHazp4WFptDm6d3od ahozyoo1l4JX2EifnTDhwICamA18qo6Fue6KDqgwklzPjDo4dQASrhNhd+WqlLkOrkMNeb 3r8U1Zgyk/Bpm8UBnXGSckxn9njGZXY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-613-8E4bpHz0Mj-o6731ga3LPw-1; Wed, 13 Sep 2023 08:32:27 -0400 X-MC-Unique: 8E4bpHz0Mj-o6731ga3LPw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2B862101FAB9; Wed, 13 Sep 2023 12:32:27 +0000 (UTC) Received: from localhost (unknown [10.42.28.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id E5DB640C2009; Wed, 13 Sep 2023 12:32:26 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Cc: Christophe Lyon Subject: [PATCH] libstdc++: Remove some more unconditional uses of atomics Date: Wed, 13 Sep 2023 13:31:40 +0100 Message-ID: <20230913123226.2083892-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Tested x86_64-linux and aarch64-linux. I intend to push this to trunk. -- >8 -- These atomics cause linker errors on arm4t where __sync_synchronize is not defined. For single-threaded targets we don't need the atomics. libstdc++-v3/ChangeLog: * include/experimental/io_context (io_context) [!_GLIBCXX_HAS_GTHREADS]: Use a plain integer for _M_work_count for single-threaded targets. * src/c++17/memory_resource.cc [!_GLIBCXX_HAS_GTHREADS] (atomic_mem_res): Use unsynchronized type for single-threaded targets. --- libstdc++-v3/include/experimental/io_context | 4 ++ libstdc++-v3/src/c++17/memory_resource.cc | 49 ++++++++++---------- 2 files changed, 29 insertions(+), 24 deletions(-) diff --git a/libstdc++-v3/include/experimental/io_context b/libstdc++-v3/include/experimental/io_context index c59f8c8e73b..c878d5a7025 100644 --- a/libstdc++-v3/include/experimental/io_context +++ b/libstdc++-v3/include/experimental/io_context @@ -562,7 +562,11 @@ inline namespace v1 } }; +#ifdef _GLIBCXX_HAS_GTHREADS atomic _M_work_count; +#else + count_type _M_work_count; +#endif mutable execution_context::mutex_type _M_mtx; queue> _M_op; bool _M_stopped = false; diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc index c0c7cf0cf83..63856eadaf5 100644 --- a/libstdc++-v3/src/c++17/memory_resource.cc +++ b/libstdc++-v3/src/c++17/memory_resource.cc @@ -27,9 +27,9 @@ #include #include // has_single_bit, bit_ceil, bit_width #include +#include // std::__exchange #if ATOMIC_POINTER_LOCK_FREE != 2 # include // std::mutex, std::lock_guard -# include // std::__exchange #endif #if __has_cpp_attribute(clang::require_constant_initialization) @@ -94,10 +94,31 @@ namespace pmr __constinit constant_init newdel_res{}; __constinit constant_init null_res{}; -#if ATOMIC_POINTER_LOCK_FREE == 2 + +#ifndef _GLIBCXX_HAS_GTHREADS +# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED + // Single-threaded, no need for synchronization + struct atomic_mem_res + { + constexpr + atomic_mem_res(memory_resource* r) : val(r) { } + + memory_resource* val; + + memory_resource* load(std::memory_order) const + { + return val; + } + + memory_resource* exchange(memory_resource* r, std::memory_order) + { + return std::__exchange(val, r); + } + }; +#elif ATOMIC_POINTER_LOCK_FREE == 2 using atomic_mem_res = atomic; # define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED -#elif defined(_GLIBCXX_HAS_GTHREADS) +#else // Can't use pointer-width atomics, define a type using a mutex instead: struct atomic_mem_res { @@ -123,27 +144,7 @@ namespace pmr return std::__exchange(val, r); } }; -#else -# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED - // Single-threaded, no need for synchronization - struct atomic_mem_res - { - constexpr - atomic_mem_res(memory_resource* r) : val(r) { } - - memory_resource* val; - - memory_resource* load(std::memory_order) const - { - return val; - } - - memory_resource* exchange(memory_resource* r, std::memory_order) - { - return std::__exchange(val, r); - } - }; -#endif // ATOMIC_POINTER_LOCK_FREE == 2 +#endif #ifdef _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED __constinit constant_init default_res{&newdel_res.obj}; -- 2.41.0