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/**********************************************************************
Audacity: A Digital Audio Editor
@file Observer.cpp
@brief Publisher-subscriber pattern, also known as Observer
Paul Licameli
**********************************************************************/
#include "Observer.h"
namespace Observer {
namespace detail {
void RecordBase::Unlink() noexcept
{
auto pPrev = prev.lock();
assert(pPrev); // See RecordList constructor and PushFront
// Do not move from next, see Visit
if (auto &pNext = (pPrev->next = next))
pNext->prev = move(prev);
}
RecordList::RecordList( ExceptionPolicy *pPolicy, Visitor visitor )
: m_pPolicy{ pPolicy }
, m_visitor{ visitor }
{
assert(m_visitor); // precondition
}
RecordList::~RecordList() noexcept
{
//! Non-defaulted destructor. Beware stack growth
auto pRecord = move(next);
while (pRecord)
pRecord = move(pRecord->next);
}
Subscription RecordList::Subscribe(std::shared_ptr<RecordBase> pRecord)
{
assert(pRecord); // precondition
auto result = Subscription{ pRecord };
if (auto &pNext = (pRecord->next = move(next)))
pNext->prev = pRecord;
pRecord->prev = weak_from_this();
next = move(pRecord);
return result;
}
bool RecordList::Visit(const void *arg)
{
assert(m_visitor); // See constructor
if (m_pPolicy)
m_pPolicy->OnBeginPublish();
bool result = false;
for (auto pRecord = next; pRecord; pRecord = pRecord->next) {
try {
if (m_visitor(*pRecord, arg)) {
result = true;
break;
}
// pRecord might have been removed from the list by the callback,
// but pRecord->next is unchanged. We won't see callbacks added by
// the callback, because they are earlier in the list.
}
catch (...) {
if (m_pPolicy && m_pPolicy->OnEachFailedCallback()) {
result = true;
break;
}
}
}
// Intentionally not in a finally():
if (m_pPolicy)
m_pPolicy->OnEndPublish();
return result;
}
}
ExceptionPolicy::~ExceptionPolicy() noexcept = default;
Subscription::Subscription() = default;
Subscription::Subscription(std::weak_ptr<detail::RecordBase> pRecord)
: m_wRecord{ move(pRecord) } {}
Subscription::Subscription(Subscription &&) = default;
Subscription &Subscription::operator=(Subscription &&other)
{
const bool inequivalent =
m_wRecord.owner_before(other.m_wRecord) ||
other.m_wRecord.owner_before(m_wRecord);
if (inequivalent) {
Reset();
m_wRecord = move(other.m_wRecord);
}
return *this;
}
void Subscription::Reset() noexcept
{
if (auto pRecord = m_wRecord.lock())
pRecord->Unlink();
m_wRecord.reset();
}
}
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