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/*************************************************************************
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* Copyright 2008 by Sun Microsystems, Inc.
*
* OpenOffice.org - a multi-platform office productivity suite
*
* $RCSfile: instance.hxx,v $
* $Revision: 1.10 $
*
* This file is part of OpenOffice.org.
*
* OpenOffice.org is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 3
* only, as published by the Free Software Foundation.
*
* OpenOffice.org is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License version 3 for more details
* (a copy is included in the LICENSE file that accompanied this code).
*
* You should have received a copy of the GNU Lesser General Public License
* version 3 along with OpenOffice.org. If not, see
* <http://www.openoffice.org/license.html>
* for a copy of the LGPLv3 License.
*
************************************************************************/
#if !defined INCLUDED_RTL_INSTANCE_HXX
#define INCLUDED_RTL_INSTANCE_HXX
#include "osl/doublecheckedlocking.h"
#include "osl/getglobalmutex.hxx"
namespace {
/** A non-broken version of the double-checked locking pattern.
See
<http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
for a description of double-checked locking, why it is broken, and how it
can be fixed. Always use this template instead of spelling out the
double-checked locking pattern explicitly, and only in those rare cases
where that is not possible and you have to spell it out explicitly, at
least call OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() at the right
places. That way, all platform-dependent code to make double-checked
locking work can be kept in one place.
Usage scenarios:
1 Static instance (most common case)
Pattern:
T * getInstance()
{
static T * pInstance = 0;
if (!pInstance)
{
::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
if (!pInstance)
{
static T aInstance;
pInstance = &aInstance;
}
}
return pInstance;
}
Code:
#include "rtl/instance.hxx"
#include "osl/getglobalmutex.hxx"
namespace {
struct Init
{
T * operator()()
{
static T aInstance;
return &aInstance;
}
};
}
T * getInstance()
{
return rtl_Instance< T, Init, ::osl::MutexGuard,
::osl::GetGlobalMutex >::create(
Init(), ::osl::GetGlobalMutex());
}
2 Dynamic instance
Pattern:
T * getInstance()
{
static T * pInstance = 0;
if (!pInstance)
{
::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
if (!pInstance)
pInstance = new T;
}
return pInstance;
}
Code:
#include "rtl/instance.hxx"
#include "osl/getglobalmutex.hxx"
namespace {
struct Init
{
T * operator()()
{
return new T;
}
};
}
T * getInstance()
{
return rtl_Instance< T, Init, ::osl::MutexGuard,
::osl::GetGlobalMutex >::create(
Init(), ::osl::GetGlobalMutex());
}
3 Other guard/mutex
Pattern:
T * getInstance()
{
static T * pInstance = 0;
if (!pInstance)
{
SomeGuard aGuard(pSomeMutex);
if (!pInstance)
{
static T aInstance;
pInstance = &aInstance;
}
}
return pInstance;
}
Code:
#include "rtl/instance.hxx"
namespace {
struct InitInstance
{
T * operator()()
{
static T aInstance;
return &aInstance;
}
};
struct InitGuard
{
SomeMutex * operator()()
{
return pSomeMutex;
}
};
}
T * getInstance()
{
return rtl_Instance< T, InitInstance,
SomeGuard, InitGuard >::create(
InitInstance(), InitMutex());
}
4 Calculate extra data
Pattern:
T * getInstance()
{
static T * pInstance = 0;
if (!pInstance)
{
Data aData(...);
::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
if (!pInstance)
{
static T aInstance(aData);
pInstance = &aInstance;
}
}
return pInstance;
}
Code:
#include "rtl/instance.hxx"
#include "osl/getglobalmutex.hxx"
namespace {
struct InitInstance
{
T * operator()()
{
static T aInstance;
return &aInstance;
}
}
struct InitData
{
Data const & operator()()
{
return ...;
}
}
}
T * getInstance()
{
return rtl_Instance< T, InitInstance,
::osl::Mutex, ::osl::GetGlobalMutex,
Data, InitData >::create(
InitInstance(), ::osl::GetGlobalMutex(), InitData());
}
Some comments:
For any instantiation of rtl_Instance, at most one call to a create method
may occur in the program code: Each occurance of a create method within
the program code is supposed to return a fresh object instance on the
first call, and that same object instance on subsequent calls; but
independent occurances of create methods are supposed to return
independent object instances. Since there is a one-to-one correspondence
between object instances and instantiations of rtl_Instance, the
requirement should be clear. One measure to enforce the requirement is
that rtl_Instance lives in an unnamed namespace, so that instantiations of
rtl_Instance in different translation units will definitely be different
instantiations. A drawback of that measure is that the name of the class
needs a funny "hand coded" prefix "rtl_" instead of a proper namespace
prefix like "::rtl::".
A known problem with this template is when two occurences of calls to
create methods with identical template arguments appear in one translation
unit. Those two places will share a single object instance. This can be
avoided by using different Init structs (see the above code samples) in
the two places.
There is no need to make m_pInstance volatile, in order to avoid usage of
stale copies of m_pInstance: At the first check, a thread will see that
m_pInstance contains either 0 or a valid pointer. If it contains a valid
pointer, it cannot be stale, and that pointer is used. If it contains 0,
acquiring the mutex will ensure that the second check sees a non-stale
value in all cases.
On some compilers, the create methods would not be inlined if they
contained any static variables, so m_pInstance is made a class member
instead (and the create methods are inlined). But on MSC, the definition
of the class member m_pInstance would cause compilation to fail with an
internal compiler error. Since MSC is able to inline methods containing
static variables, m_pInstance is moved into the methods there. Note that
this only works well because for any instantiation of rtl_Instance at most
one call to a create method should be present, anyway.
*/
template< typename Inst, typename InstCtor,
typename Guard, typename GuardCtor,
typename Data = int, typename DataCtor = int >
class rtl_Instance
{
public:
static inline Inst * create(InstCtor aInstCtor, GuardCtor aGuardCtor)
{
#if defined _MSC_VER
static Inst * m_pInstance = 0;
#endif // _MSC_VER
Inst * p = m_pInstance;
if (!p)
{
Guard aGuard(aGuardCtor());
p = m_pInstance;
if (!p)
{
p = aInstCtor();
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
m_pInstance = p;
}
}
else
{
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
}
return p;
}
static inline Inst * create(InstCtor aInstCtor, GuardCtor aGuardCtor,
DataCtor aDataCtor)
{
#if defined _MSC_VER
static Inst * m_pInstance = 0;
#endif // _MSC_VER
Inst * p = m_pInstance;
if (!p)
{
Data aData(aDataCtor());
Guard aGuard(aGuardCtor());
p = m_pInstance;
if (!p)
{
p = aInstCtor(aData);
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
m_pInstance = p;
}
}
else
{
OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
}
return p;
}
private:
#if !defined _MSC_VER
static Inst * m_pInstance;
#endif // _MSC_VER
};
#if !defined _MSC_VER
template< typename Inst, typename InstCtor,
typename Guard, typename GuardCtor,
typename Data, typename DataCtor >
Inst *
rtl_Instance< Inst, InstCtor, Guard, GuardCtor, Data, DataCtor >::m_pInstance
= 0;
#endif // _MSC_VER
}
namespace rtl {
/** Helper base class for a late-initialized (default-constructed)
static variable, implementing the double-checked locking pattern correctly.
@derive
Derive from this class (common practice), e.g.
<pre>
struct MyStatic : public rtl::Static<MyType, MyStatic> {};
...
MyType & rStatic = MyStatic::get();
...
</pre>
@tplparam T
variable's type
@tplparam Unique
Implementation trick to make the inner static holder unique,
using the outer class
(the one that derives from this base class)
*/
template<typename T, typename Unique>
class Static {
public:
/** Gets the static. Mutual exclusion is performed using the
osl global mutex.
@return
static variable
*/
static T & get() {
return *rtl_Instance<
T, StaticInstance,
::osl::MutexGuard, ::osl::GetGlobalMutex >::create(
StaticInstance(), ::osl::GetGlobalMutex() );
}
private:
struct StaticInstance {
T * operator () () {
static T instance;
return &instance;
}
};
};
/** Helper class for a late-initialized static aggregate, e.g. an array,
implementing the double-checked locking pattern correctly.
@tplparam T
aggregate's element type
@tplparam InitAggregate
initializer functor class
*/
template<typename T, typename InitAggregate>
class StaticAggregate {
public:
/** Gets the static aggregate, late-initializing.
Mutual exclusion is performed using the osl global mutex.
@return
aggregate
*/
static T * get() {
return rtl_Instance<
T, InitAggregate,
::osl::MutexGuard, ::osl::GetGlobalMutex >::create(
InitAggregate(), ::osl::GetGlobalMutex() );
}
};
/** Helper base class for a late-initialized static variable,
implementing the double-checked locking pattern correctly.
@derive
Derive from this class (common practice),
providing an initializer functor class, e.g.
<pre>
struct MyStatic : public rtl::StaticWithInit<MyType, MyStatic> {
MyType operator () () {
...
return MyType( ... );
}
};
...
MyType & rStatic = MyStatic::get();
...
</pre>
@tplparam T
variable's type
@tplparam InitData
initializer functor class
@tplparam Unique
Implementation trick to make the inner static holder unique,
using the outer class
(the one that derives from this base class).
Default is InitData (common practice).
@tplparam Data
Initializer functor's return type.
Default is T (common practice).
*/
template<typename T, typename InitData,
typename Unique = InitData, typename Data = T>
class StaticWithInit {
public:
/** Gets the static. Mutual exclusion is performed using the
osl global mutex.
@return
static variable
*/
static T & get() {
return *rtl_Instance<
T, StaticInstanceWithInit,
::osl::MutexGuard, ::osl::GetGlobalMutex,
Data, InitData >::create( StaticInstanceWithInit(),
::osl::GetGlobalMutex(),
InitData() );
}
private:
struct StaticInstanceWithInit {
T * operator () ( Data d ) {
static T instance(d);
return &instance;
}
};
};
} // namespace rtl
#endif // INCLUDED_RTL_INSTANCE_HXX
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