/*
- Copyright (C) 2000-2007 Paul Davis
+ Copyright (C) 2000-2007 Paul Davis
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
#define __pbd_rcu_h__
#include "boost/shared_ptr.hpp"
-#include "glibmm/thread.h"
-
-#include <list>
+#include "glibmm/threads.h"
-/* This header file defines a set of classes to implement Read-Copy-Update. we do not attempt to define RCU here - use google.
-
- The design consists of two parts. An RCUManager is an object which takes over management of a pointer to another object.
+#include <list>
+
+/** @file Defines a set of classes to implement Read-Copy-Update. We do not attempt to define RCU here - use google.
+
+ The design consists of two parts: an RCUManager and an RCUWriter.
+*/
+
+/** An RCUManager is an object which takes over management of a pointer to another object.
It provides three key methods:
- - reader() : obtains a shared pointer to the managed object that may be used for reading, without synchronization
+ - reader() : obtains a shared pointer to the managed object that may be used for reading, without synchronization
- write_copy() : obtains a shared pointer to the object that may be used for writing/modification
- update() : accepts a shared pointer to a (presumed) modified instance of the object and causes all
- future reader() and write_copy() calls to use that instance.
+ future reader() and write_copy() calls to use that instance.
- Any existing users of the value returned by reader() can continue to use their copy even as a write_copy()/update() takes place.
+ Any existing users of the value returned by reader() can continue to use their copy even as a write_copy()/update() takes place.
The RCU manager will manage the various instances of "the managed object" in a way that is transparent to users of the manager
and managed object.
*/
-
-
template<class T>
class RCUManager
{
public:
-
+
RCUManager (T* new_rcu_value) {
x.m_rcu_value = new boost::shared_ptr<T> (new_rcu_value);
}
-
+
virtual ~RCUManager() { delete x.m_rcu_value; }
-
- boost::shared_ptr<T> reader () const { return *((boost::shared_ptr<T> *) g_atomic_pointer_get (&x.gptr)); }
-
+
+ boost::shared_ptr<T> reader () const { return *((boost::shared_ptr<T> *) g_atomic_pointer_get (&x.gptr)); }
+
/* this is an abstract base class - how these are implemented depends on the assumptions
that one can make about the users of the RCUManager. See SerializedRCUManager below
for one implementation.
protected:
/* ordinarily this would simply be a declaration of a ptr to a shared_ptr<T>. however, the atomic
operations that we are using (from glib) have sufficiently strict typing that it proved hard
- to get them to accept even a cast value of the ptr-to-shared-ptr() as the argument to get()
+ to get them to accept even a cast value of the ptr-to-shared-ptr() as the argument to get()
and comp_and_exchange(). Consequently, we play a litle trick here that relies on the fact
that sizeof(A*) == sizeof(B*) no matter what the types of A and B are. for most purposes
we will use x.m_rcu_value, but when we need to use an atomic op, we use x.gptr. Both expressions
};
-/* Serialized RCUManager implements the RCUManager interface. It is based on the
+/** Serialized RCUManager implements the RCUManager interface. It is based on the
following key assumption: among its users we have readers that are bound by
RT time constraints, and writers who are not. Therefore, we do not care how
slow the write_copy()/update() operations are, or what synchronization
primitives they use.
-
+
Because of this design assumption, this class will serialize all
writers. That is, objects calling write_copy()/update() will be serialized by
a mutex. Only a single writer may be in the middle of write_copy()/update();
The class maintains a lock-protected "dead wood" list of old value of
*m_rcu_value (i.e. shared_ptr<T>). The list is cleaned up every time we call
write_copy(). If the list is the last instance of a shared_ptr<T> that
- references the object (determined by inspecting its use_count()) then we
+ references the object (determined by shared_ptr::unique()) then we
erase it from the list, thus deleting the object it points to. This is lazy
destruction - the SerializedRCUManager assumes that there will sufficient
calls to write_copy() to ensure that we do not inadvertently leave objects
must be used with significant caution, although the use of shared_ptr<T>
means that no actual objects will be deleted incorrectly if this is misused.
*/
-
-
template<class T>
class SerializedRCUManager : public RCUManager<T>
{
public:
-
+
SerializedRCUManager(T* new_rcu_value)
: RCUManager<T>(new_rcu_value)
{
-
}
-
+
boost::shared_ptr<T> write_copy ()
{
m_lock.lock();
typename std::list<boost::shared_ptr<T> >::iterator i;
for (i = m_dead_wood.begin(); i != m_dead_wood.end(); ) {
- if ((*i).use_count() == 1) {
+ if ((*i).unique()) {
i = m_dead_wood.erase (i);
} else {
++i;
*/
current_write_old = RCUManager<T>::x.m_rcu_value;
-
+
boost::shared_ptr<T> new_copy (new T(**current_write_old));
return new_copy;
be called or we will cause another writer to stall.
*/
}
-
+
bool update (boost::shared_ptr<T> new_value)
{
/* we still hold the write lock - other writers are locked out */
/* update, by atomic compare&swap. Only succeeds if the old
value has not been changed.
-
+
XXX but how could it? we hold the freakin' lock!
*/
bool ret = g_atomic_pointer_compare_and_exchange (&RCUManager<T>::x.gptr,
(gpointer) current_write_old,
(gpointer) new_spp);
-
+
if (ret) {
// successful update : put the old value into dead_wood,
}
void flush () {
- Glib::Mutex::Lock lm (m_lock);
+ Glib::Threads::Mutex::Lock lm (m_lock);
m_dead_wood.clear ();
}
-
+
private:
- Glib::Mutex m_lock;
+ Glib::Threads::Mutex m_lock;
boost::shared_ptr<T>* current_write_old;
std::list<boost::shared_ptr<T> > m_dead_wood;
};
-/* RCUWriter is a convenience object that implements write_copy/update via
- lifetime management. Creating the object obtais a writable copy, which can
+/** RCUWriter is a convenience object that implements write_copy/update via
+ lifetime management. Creating the object obtains a writable copy, which can
be obtained via the get_copy() method; deleting the object will update
the manager's copy. Code doing a write/update thus looks like:
} <= writer goes out of scope, update invoked
*/
-
template<class T>
class RCUWriter
{
public:
-
+
RCUWriter(RCUManager<T>& manager)
: m_manager(manager) {
- m_copy = m_manager.write_copy();
+ m_copy = m_manager.write_copy();
}
-
+
~RCUWriter() {
- if(m_copy.use_count() == 1) {
+ if (m_copy.unique()) {
/* As intended, our copy is the only reference
to the object pointed to by m_copy. Update
the manager with the (presumed) modified
copy was private to this particular RCUWriter. Doing
so will not actually break anything but it violates
the design intention here and so we do not bother to
- update the manager's copy.
+ update the manager's copy.
XXX should we print a warning about this?
*/
}
-
+
}
-
+
boost::shared_ptr<T> get_copy() const { return m_copy; }
-
+
private:
RCUManager<T>& m_manager;
boost::shared_ptr<T> m_copy;
projects / ardour.git / blobdiff