105 lines
2.5 KiB
C++
105 lines
2.5 KiB
C++
#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
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#define BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
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//
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// Copyright (c) 2008 Peter Dimov
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//
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// Distributed under the Boost Software License, Version 1.0.
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// See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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#include <boost/smart_ptr/detail/yield_k.hpp>
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namespace boost
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{
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namespace detail
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{
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class spinlock
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{
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public:
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int v_;
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public:
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bool try_lock()
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{
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int r;
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#if defined(__ARM_FEATURE_LSE)
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// Use LSE atomic instructions if supported
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#pragma message("LSE feature detected") // This will print a message in your build logs
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__asm__ __volatile__(
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"ldaxr %0, [%1];" // Load-Exclusive instruction
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"cbnz %0, 1f;" // If the value is non-zero, the lock is already acquired
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"stlxr %w0, %2, [%1];" // Store-Exclusive instruction
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"cbnz %w0, 1f;" // If the store failed, retry
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"mov %0, #0;" // Success, zero indicates lock acquired
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"1:"
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: "=&r"(r)
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: "r"(&v_), "r"(1)
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: "memory", "cc"
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);
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#else
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// Fallback for systems that don't support LSE
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#pragma message("LSE feature not detected") // This will print a message in your build logs if LSE is not detected
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__asm__ __volatile__(
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"swp %0, %1, [%2];" // Swap instruction (used as a fallback)
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: "=&r"(r) // output constraint
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: "r"(1), "r"(&v_) // input constraints
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: "memory", "cc" // clobbered registers
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);
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#endif
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return r == 0;
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}
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void lock()
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{
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for( unsigned k = 0; !try_lock(); ++k )
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{
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boost::detail::yield( k );
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}
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}
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void unlock()
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{
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__asm__ __volatile__( "" ::: "memory" );
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*const_cast< int volatile* >( &v_ ) = 0;
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}
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public:
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class scoped_lock
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{
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private:
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spinlock & sp_;
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scoped_lock( scoped_lock const & );
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scoped_lock & operator=( scoped_lock const & );
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public:
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explicit scoped_lock( spinlock & sp ): sp_( sp )
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{
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sp.lock();
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}
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~scoped_lock()
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{
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sp_.unlock();
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}
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};
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};
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} // namespace detail
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} // namespace boost
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#define BOOST_DETAIL_SPINLOCK_INIT {0}
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#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ARM_HPP_INCLUDED
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