weak_ptr made thread safe, shared->weak conversions, lightweight_mutex added.

[SVN r12786]

include/boost/detail/lightweight_mutex.hpp

@@ -0,0 +1,49 @@
+#ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
+#define BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
+
+#if _MSC_VER >= 1020
+#pragma once
+#endif
+
+//
+//  boost/detail/lightweight_mutex.hpp - lightweight mutex
+//
+//  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  typedef <implementation-defined> boost::detail::lightweight_mutex;
+//
+//  boost::detail::lightweight_mutex meets the Mutex concept requirements
+//  See http://www.boost.org/libs/thread/doc/mutex_concept.html#Mutex
+//
+//  * Used by the smart pointer library
+//  * Performance oriented
+//  * Header-only implementation
+//  * Small memory footprint
+//  * Not a general purpose mutex, use boost::mutex, CRITICAL_SECTION or
+//    pthread_mutex instead.
+//  * Never spin in a tight lock/do-something/unlock loop, since
+//    lightweight_mutex does not guarantee fairness.
+//  * Never keep a lightweight_mutex locked for long periods.
+//
+
+
+#include <boost/config.hpp>
+
+#ifndef BOOST_HAS_THREADS
+#  include <boost/detail/lwm_nop.hpp>
+#elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
+#  include <boost/detail/lwm_win32.hpp>
+//#elif defined(linux) || defined(__linux) || defined(__linux__)
+//#  include <boost/detail/lwm_linux.hpp>
+#elif defined(BOOST_HAS_PTHREADS)
+#  include <boost/detail/lwm_pthreads.hpp>
+#else
+#  include <boost/detail/lwm_nop.hpp>
+#endif
+
+#endif // #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED

include/boost/detail/lwm_nop.hpp

@@ -0,0 +1,57 @@
+#ifndef BOOST_DETAIL_LWM_NOP_HPP_INCLUDED
+#define BOOST_DETAIL_LWM_NOP_HPP_INCLUDED
+
+#if _MSC_VER >= 1020
+#pragma once
+#endif
+
+//
+//  boost/detail/lwm_nop.hpp
+//
+//  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+
+namespace boost
+{
+
+namespace detail
+{
+
+class lightweight_mutex
+{
+private:
+
+    lightweight_mutex(lightweight_mutex const &);
+    lightweight_mutex & operator=(lightweight_mutex const &);
+
+public:
+
+    lightweight_mutex()
+    {
+    }
+
+    class scoped_lock
+    {
+    private:
+
+        scoped_lock(scoped_lock const &);
+        scoped_lock & operator=(scoped_lock const &);
+
+    public:
+
+        explicit scoped_lock(lightweight_mutex &)
+        {
+        }
+    };
+};
+
+} // namespace detail
+
+} // namespace boost
+
+#endif // #ifndef BOOST_DETAIL_LWM_NOP_HPP_INCLUDED

include/boost/detail/lwm_pthreads.hpp

@@ -0,0 +1,78 @@
+#ifndef BOOST_DETAIL_LWM_PTHREADS_HPP_INCLUDED
+#define BOOST_DETAIL_LWM_PTHREADS_HPP_INCLUDED
+
+#if _MSC_VER >= 1020
+#pragma once
+#endif
+
+//
+//  boost/detail/lwm_pthreads.hpp
+//
+//  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+
+#include <pthread.h>
+
+namespace boost
+{
+
+namespace detail
+{
+
+class lightweight_mutex
+{
+private:
+
+    pthread_mutex_t m_;
+
+    lightweight_mutex(lightweight_mutex const &);
+    lightweight_mutex & operator=(lightweight_mutex const &);
+
+public:
+
+    lightweight_mutex()
+    {
+        pthread_mutex_init(&m_, 0);
+    }
+
+    ~lightweight_mutex()
+    {
+        pthread_mutex_destroy(&m_);
+    }
+
+    class scoped_lock;
+    friend class scoped_lock;
+
+    class scoped_lock
+    {
+    private:
+
+        pthread_mutex_t & m_;
+
+        scoped_lock(scoped_lock const &);
+        scoped_lock & operator=(scoped_lock const &);
+
+    public:
+
+        scoped_lock(lightweight_mutex & m): m_(m.m_)
+        {
+            pthread_mutex_lock(&m_);
+        }
+
+        ~scoped_lock()
+        {
+            pthread_mutex_unlock(&m_);
+        }
+    };
+};
+
+} // namespace detail
+
+} // namespace boost
+
+#endif // #ifndef BOOST_DETAIL_LWM_PTHREADS_HPP_INCLUDED

include/boost/detail/lwm_win32.hpp

@@ -0,0 +1,84 @@
+#ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED
+#define BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED
+
+#if _MSC_VER >= 1020
+#pragma once
+#endif
+
+//
+//  boost/detail/lwm_win32.hpp
+//
+//  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+
+namespace boost
+{
+
+namespace detail
+{
+
+// Avoid #including <windows.h>
+
+namespace win32
+{
+extern "C" __declspec(dllimport) long __stdcall InterlockedExchange(long volatile *, long);
+extern "C" __declspec(dllimport) void __stdcall Sleep(unsigned long);
+}
+
+class lightweight_mutex
+{
+private:
+
+    long l_;
+
+    lightweight_mutex(lightweight_mutex const &);
+    lightweight_mutex & operator=(lightweight_mutex const &);
+
+public:
+
+    lightweight_mutex(): l_(0)
+    {
+    }
+
+    class scoped_lock;
+    friend class scoped_lock;
+
+    class scoped_lock
+    {
+    private:
+
+        lightweight_mutex & m_;
+
+        scoped_lock(scoped_lock const &);
+        scoped_lock & operator=(scoped_lock const &);
+
+    public:
+
+        explicit scoped_lock(lightweight_mutex & m): m_(m)
+        {
+            while( win32::InterlockedExchange(&m_.l_, 1) ) win32::Sleep(0);
+        }
+
+        ~scoped_lock()
+        {
+            win32::InterlockedExchange(&m_.l_, 0);
+
+            // Note: adding a win32::Sleep(0) here will make
+            // the mutex more fair and will increase the overall
+            // performance of the application substantially in
+            // high contention situations, but will penalize the
+            // low contention / single thread case up to 5x
+        }
+    };
+};
+
+} // namespace detail
+
+} // namespace boost
+
+#endif // #ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED

include/boost/detail/shared_count.hpp

@@ -23,9 +23,10 @@
 #endif
 
 #include <boost/checked_delete.hpp>
-#include <boost/detail/atomic_count.hpp>
+#include <boost/detail/lightweight_mutex.hpp>
 
-#include <functional>         // for std::less
+#include <functional>       // for std::less
+#include <exception>        // for std::exception
 
 namespace boost
 {
@@ -33,11 +34,19 @@ namespace boost
 namespace detail
 {
 
-class counted_base
+class bad_weak_to_shared_cast: public std::exception
 {
 public:
 
-    typedef atomic_count count_type;
+    virtual char const * what() const throw()
+    {
+        return "bad_weak_to_shared_cast";
+    }
+};
+
+class counted_base
+{
+public:
 
     // pre: initial_use_count <= initial_weak_count
 
@@ -63,20 +72,31 @@ public:
     {
     }
 
-    void add_ref() // nothrow
+    void add_ref()
     {
+        lightweight_mutex::scoped_lock lock(mtx_);
+        if(use_count_ == 0) throw bad_weak_to_shared_cast();
         ++use_count_;
         ++weak_count_;
     }
 
     void release() // nothrow
     {
-        if(--use_count_ == 0)
+        long new_use_count;
+        long new_weak_count;
+
+        {
+            lightweight_mutex::scoped_lock lock(mtx_);
+            new_use_count = --use_count_;
+            new_weak_count = --weak_count_;
+        }
+
+        if(new_use_count == 0)
         {
             dispose();
         }
 
-        if(--weak_count_ == 0)
+        if(new_weak_count == 0)
         {
             // not a direct 'delete this', because the inlined
             // release() may use a different heap manager
@@ -86,12 +106,20 @@ public:
 
     void weak_add_ref() // nothrow
     {
+        lightweight_mutex::scoped_lock lock(mtx_);
         ++weak_count_;
     }
 
     void weak_release() // nothrow
     {
-        if(--weak_count_ == 0)
+        long new_weak_count;
+
+        {
+            lightweight_mutex::scoped_lock lock(mtx_);
+            new_weak_count = --weak_count_;
+        }
+
+        if(new_weak_count == 0)
         {
             self_deleter_(this);
         }
@@ -99,6 +127,7 @@ public:
 
     long use_count() const // nothrow
     {
+        lightweight_mutex::scoped_lock lock(mtx_);
         return use_count_;
     }
 
@@ -114,9 +143,9 @@ private:
 
     // inv: use_count_ <= weak_count_
 
-    count_type use_count_;
-    count_type weak_count_;
-
+    long use_count_;
+    long weak_count_;
+    mutable lightweight_mutex mtx_;
     void (*self_deleter_) (counted_base *);
 };
 
@@ -191,6 +220,8 @@ public:
         pi_->add_ref();
     }
 
+    explicit shared_count(weak_count const & r); // throws bad_weak_to_shared_cast when r.use_count() == 0
+
     shared_count & operator= (shared_count const & r) // nothrow
     {
         counted_base * tmp = r.pi_;
@@ -235,6 +266,8 @@ private:
 
     counted_base * pi_;
 
+    friend class shared_count;
+
 public:
 
     weak_count(): pi_(new counted_base(0, 1)) // can throw
@@ -299,6 +332,11 @@ public:
     }
 };
 
+inline shared_count::shared_count(weak_count const & r): pi_(r.pi_)
+{
+    pi_->add_ref();
+}
+
 } // namespace detail
 
 } // namespace boost

include/boost/shared_ptr.hpp

@@ -97,6 +97,10 @@ public:
 
 //  generated copy constructor, assignment, destructor are fine
 
+    explicit shared_ptr(weak_ptr<T> const & r): px(r.px), pn(r.pn) // may throw
+    {
+    }
+
     template<typename Y>
     shared_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
     {
@@ -191,6 +195,20 @@ public:
         return pn.use_count();
     }
 
+    // implicit conversion to "bool"
+
+    typedef long (this_type::*bool_type)() const;
+
+    operator bool_type() const // never throws
+    {
+        return px == 0? 0: &this_type::use_count;
+    }
+
+    bool operator! () const // never throws
+    {
+        return px == 0;
+    }
+
     void swap(shared_ptr<T> & other) // never throws
     {
         std::swap(px, other.px);

include/boost/weak_ptr.hpp

@@ -30,6 +30,7 @@ private:
 
     // Borland 5.5.1 specific workarounds
     typedef weak_ptr<T> this_type;
+    typedef shared_ptr<T> shared_type;
 
 public:
 
@@ -95,23 +96,32 @@ public:
         this_type().swap(*this);
     }
 
-    T * get() const // never throws
+    shared_type get() const // never throws
     {
-        return use_count() == 0? 0: px;
+        // optimization: avoid throw overhead
+        if(use_count() == 0)
+        {
+            return shared_type();
+        }
+
+        try
+        {
+            return shared_type(*this);
+        }
+        catch(boost::detail::bad_weak_to_shared_cast const &)
+        {
+            return shared_type();
+        }
     }
 
-    typename detail::shared_ptr_traits<T>::reference operator* () const // never throws
-    {
-        element_type * p = get();
-        BOOST_ASSERT(p != 0);
-        return *p;
-    }
+    // operator* has been removed; it's unsafe.
 
-    T * operator-> () const // never throws
+    // operator-> retained for convenience, since it's safe
+    // in its current form.
+
+    shared_type operator-> () const // may throw
     {
-        element_type * p = get();
-        BOOST_ASSERT(p != 0);
-        return p;
+        return shared_type(*this);
     }
     
     long use_count() const // never throws
@@ -119,7 +129,21 @@ public:
         return pn.use_count();
     }
 
-    void swap(weak_ptr<T> & other) // never throws
+    // implicit conversion to "bool"
+
+    typedef long (this_type::*bool_type)() const;
+
+    operator bool_type() const // never throws
+    {
+        return use_count() == 0? 0: &this_type::use_count;
+    }
+
+    bool operator! () const // never throws
+    {
+        return use_count() == 0;
+    }
+
+    void swap(this_type & other) // never throws
     {
         std::swap(px, other.px);
         pn.swap(other.pn);
@@ -138,6 +162,7 @@ public:
 private:
 
     template<typename Y> friend class weak_ptr;
+    template<typename Y> friend class shared_ptr;
 
 #endif
 
@@ -198,13 +223,6 @@ template<typename T, typename U> weak_ptr<T> shared_polymorphic_downcast(weak_pt
     return shared_static_cast<T>(r);
 }
 
-// get_pointer() enables boost::mem_fn to recognize weak_ptr
-
-template<class T> inline T * get_pointer(weak_ptr<T> const & p)
-{
-    return p.get();
-}
-
 } // namespace boost
 
 #ifdef BOOST_MSVC