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pool: use weak_ptr to run destructor earlier

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Drop the ListType alias because we only use it once.  Rename ListRep to
PoolRep to better reflect what it does.

We don't need the Pool to be available to handle destroyed Pool::Handle
objects.  A weak_ptr in the Handle would detect the Pool has been
destroyed, so we don't need to track that ourselves.  As a bonus, we can
destroy the PoolRep object as soon as the Pool has been destroyed, delayed
only if there is a Handle object currently executing its destructor.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2020-12-30 16:44:53 -05:00
parent fbd1091052
commit 06062cfd96
1 changed files with 28 additions and 30 deletions
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58
include/crucible/pool.h
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@ -37,28 +37,26 @@ namespace crucible {
void clear();
private:
using ListType = list<Ptr>;
struct ListRep {
ListType m_list;
struct PoolRep {
list<Ptr> m_list;
mutex m_mutex;
bool m_destroyed = false;
Checker m_checkin;
ListRep(Checker checkin);
PoolRep(Checker checkin);
};
struct Handle {
shared_ptr<ListRep> m_list_rep;
weak_ptr<PoolRep> m_list_rep;
Ptr m_ret_ptr;
Handle(shared_ptr<ListRep> list_rep, Ptr ret_ptr);
Handle(shared_ptr<PoolRep> list_rep, Ptr ret_ptr);
~Handle();
};
Generator m_fn;
Checker m_checkout;
shared_ptr<ListRep> m_list_rep;
shared_ptr<PoolRep> m_list_rep;
};
template <class T>
Pool<T>::ListRep::ListRep(Checker checkin) :
Pool<T>::PoolRep::PoolRep(Checker checkin) :
m_checkin(checkin)
{
}
@ -67,20 +65,20 @@ namespace crucible {
Pool<T>::Pool(Generator f, Checker checkin, Checker checkout) :
m_fn(f),
m_checkout(checkout),
m_list_rep(make_shared<ListRep>(checkin))
m_list_rep(make_shared<PoolRep>(checkin))
{
}
template <class T>
Pool<T>::~Pool()
{
unique_lock<mutex> lock(m_list_rep->m_mutex);
m_list_rep->m_destroyed = true;
m_list_rep->m_list.clear();
auto list_rep = m_list_rep;
unique_lock<mutex> lock(list_rep->m_mutex);
m_list_rep.reset();
}
template <class T>
Pool<T>::Handle::Handle(shared_ptr<ListRep> list_rep, Ptr ret_ptr) :
Pool<T>::Handle::Handle(shared_ptr<PoolRep> list_rep, Ptr ret_ptr) :
m_list_rep(list_rep),
m_ret_ptr(ret_ptr)
{
@ -89,25 +87,25 @@ namespace crucible {
template <class T>
Pool<T>::Handle::~Handle()
{
unique_lock<mutex> lock(m_list_rep->m_mutex);
// Checkin prepares the object for storage and reuse.
// Neither of those will happen if there is no Pool.
// If the Pool was destroyed, just let m_ret_ptr expire.
if (!m_list_rep->m_destroyed) {
// If a checkin function is defined, call it
auto checkin = m_list_rep->m_checkin;
if (checkin) {
lock.unlock();
checkin(m_ret_ptr);
lock.lock();
}
// Place object back in pool
m_list_rep->m_list.push_front(m_ret_ptr);
auto list_rep = m_list_rep.lock();
if (!list_rep) {
return;
}
unique_lock<mutex> lock(list_rep->m_mutex);
// If a checkin function is defined, call it
auto checkin = list_rep->m_checkin;
if (checkin) {
lock.unlock();
checkin(m_ret_ptr);
lock.lock();
}
// Place object back in pool
list_rep->m_list.push_front(m_ret_ptr);
}
template <class T>
@ -132,7 +130,7 @@ namespace crucible {
lock.unlock();
}
// rv now points to a new T object that is not in the list.
// rv now points to a T object that is not in the list.
THROW_CHECK0(runtime_error, rv);
// Construct a shared_ptr for Handle which will refcount the Handle objects