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// -*- mode: c++; c-basic-offset: 2; -*-
#ifndef OBSERVERS_HH
#define OBSERVERS_HH
template<typename T>
class Observers {
private:
struct Entry {
T const item_;
unsigned int ref_;
bool deleted_;
Entry* next_;
Entry(T const& item, Entry* next)
: item_(item), ref_(0), deleted_(false), next_(next) {
}
};
public:
class Iterator {
public:
Iterator(Observers* observers)
: observers_(observers), cur_(nullptr) {
}
Iterator(Iterator const& iter)
: observers_(iter.observers_), cur_(iter.cur_) {
if (cur_) observers_->ref(cur_);
}
~Iterator() {
if (cur_) observers_->unref(cur_);
}
Iterator& operator=(Iterator const& iter) {
if (cur_) observers_->unref(cur_);
observers_ = iter.observers_;
cur_ = iter.cur_;
if (cur_) observers_->ref(cur_);
return *this;
}
bool operator==(Iterator const& iter) const {
return observers_ == iter.observers_ && cur_ == iter.cur_;
}
bool operator!=(Iterator const& iter) const {
return observers_ != iter.observers_ || cur_ != iter.cur_;
}
bool has_next() const {
auto n = cur_ ? cur_->next_ : observers_->first_;
while (n && n->deleted_) n = n->next_;
return n;
}
T const& next() {
if (cur_) {
assert(cur_->next_);
auto last = cur_;
cur_ = cur_->next_;
observers_->unref(last);
} else {
assert(observers_->first_);
cur_ = observers_->first_;
}
while (cur_ && cur_->deleted_) cur_ = cur_->next_;
assert(cur_);
observers_->ref(cur_);
return cur_->item_;
}
private:
Observers* observers_;
Entry* cur_;
};
Observers()
: first_(nullptr) {
}
~Observers() {
auto c = first_;
while (c) {
auto n = c->next_;
delete c;
c = n;
}
}
void insert(T const& item) {
first_ = new Entry(item, first_);
}
void erase(T const& item) {
if (!first_) return;
auto c = first_;
if (c->item_ == item) {
if (c->ref_ == 0) {
first_ = c->next_;
delete c;
} else {
c->deleted_ = true;
}
return;
}
while (c->next_) {
if (c->next_->item_ == item) {
if (c->next_->ref_ == 0) {
auto del = c->next_;
c->next_ = del->next_;
delete del;
} else {
c->next_->deleted_ = true;
}
return;
}
c = c->next_;
}
}
Iterator notify() {
return Iterator(this);
}
private:
void ref(Entry* entry) {
assert(entry->ref_ > 0 || !entry->deleted_);
entry->ref_++;
}
void unref(Entry* entry) {
assert(entry->ref_ > 0);
if (--entry->ref_ == 0 && entry->deleted_) {
if (entry == first_) {
first_ = entry->next_;
} else {
auto c = first_;
while (c->next_ != entry) c = c->next_;
c->next_ = entry->next_;
}
delete entry;
}
}
Entry* first_;
};
#endif // OBSERVERS_HH
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