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pool: use voidptr storage to avoid definition requirements for users

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This commit is contained in:
Danny Robson 2019-05-24 11:04:43 +10:00
parent 19409d67ca
commit fb36953135
1 changed files with 95 additions and 136 deletions
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231
pool.hpp
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@ -8,8 +8,10 @@
#pragma once
#include "debug/assert.hpp"
#include "cast.hpp"
#include "debug/assert.hpp"
#include "parallel/stack.hpp"
#include "view.hpp"
#include <atomic>
#include <new>
@ -18,116 +20,101 @@
#include <cstdint>
namespace cruft {
/// a simple pre-allocated pool for storage of PODs.
///
/// non-POD types can be stored, but there are no guarantees for calling
/// item destructors at pool destruction time.
/// A simple, thread safe, pre-allocated pool allocator.
template <typename T>
class pool {
protected:
union node;
private:
/// A collection of all unallocated slots.
parallel::stack<void*> m_available;
union node {
alignas(node*) std::atomic<node*> next;
alignas(node*) node* raw;
alignas(T) char data[sizeof(T)];
};
/// A pointer to the start of the allocated region.
void *m_store;
static_assert (std::atomic<node*>::is_always_lock_free);
// root address of allocation. used in deletion at destruction time.
node* m_head;
// the next available entry in the linked list
std::atomic<node *> m_next;
// the total number of items that could be stored
/// The total number of items for which storage has been allocated.
std::size_t m_capacity;
// the number of items currently stored.
std::atomic<size_t> m_size;
// We used to use std::aligned_storage_t and arrays/vectors proper for
// data storage. But this requires that the user has already defined
// ValueT ahead of time (given we need to call sizeof outside a deduced
// context).
//
// We tried a strategy where nodes were a union of ValueT and a
// linked-list. However this proved heinously expensive to traverse to
// find allocated objects that need to be destroyed when our destructor
// is called.
public:
///////////////////////////////////////////////////////////////////////
pool (const pool&) = delete;
pool& operator= (const pool&) = delete;
//---------------------------------------------------------------------
pool (pool &&rhs) noexcept
: m_head (nullptr)
, m_next (nullptr)
: m_available (0)
, m_capacity (0)
, m_size (0)
{
std::swap (m_head, rhs.m_head);
m_next = rhs.m_next.load ();
rhs.m_next = nullptr;
std::swap (m_capacity, rhs.m_capacity);
m_size = rhs.m_size.load ();
rhs.m_size = 0;
std::swap (m_available, rhs.m_available);
std::swap (m_store, rhs.m_store);
std::swap (m_capacity, rhs.m_capacity);
}
//---------------------------------------------------------------------
pool& operator= (pool&&);
explicit
pool (std::size_t _capacity):
m_capacity (_capacity),
m_size (0u)
{
// allocate the memory and note the base address for deletion in destructor
m_next = m_head = new node[m_capacity];
relink ();
//---------------------------------------------------------------------
explicit
pool (std::size_t _capacity)
: m_available (_capacity)
, m_store (::operator new[] (_capacity * sizeof (T), std::align_val_t {alignof (T)}))
, m_capacity (_capacity)
{
if (!m_store)
throw std::bad_alloc ();
T* elements = reinterpret_cast<T*> (m_store);
for (size_t i = 0; i < m_capacity; ++i)
m_available.push (elements + i);
}
//---------------------------------------------------------------------
~pool ()
{
clear ();
// don't check if everything's been returned as pools are often used
// for PODs which don't need to be destructed via calling release.
delete [] m_head;
::operator delete[] (
m_store,
m_capacity * sizeof (T),
std::align_val_t {alignof (T)}
);
}
// Data management
///////////////////////////////////////////////////////////////////////
[[nodiscard]] T*
allocate [[gnu::malloc]] [[gnu::returns_nonnull]] (void)
{
// double check we have enough capacity left
if (!m_next)
void *raw;
if (!m_available.pop (&raw))
throw std::bad_alloc ();
CHECK_LT (m_size, m_capacity);
// unlink the current cursor
do {
node* curr = m_next;
node* soon = curr->next;
if (m_next.compare_exchange_weak (curr, soon)) {
++m_size;
return std::launder (cruft::cast::alignment<T*> (curr));
}
} while (1);
return reinterpret_cast<T*> (raw);
}
//---------------------------------------------------------------------
void
deallocate (T *base)
deallocate (T *cooked)
{
auto soon = cruft::cast::alignment<node*> (base);
do {
node *curr = m_next;
soon->next = curr;
if (m_next.compare_exchange_weak (curr, soon)) {
--m_size;
return;
}
} while (1);
void *raw = reinterpret_cast<void*> (cooked);
if (unlikely (!m_available.push (raw)))
panic (__FUNCTION__);
}
///////////////////////////////////////////////////////////////////////
template <typename ...Args>
T*
construct (Args &&...args)
@ -142,6 +129,7 @@ namespace cruft {
}
//---------------------------------------------------------------------
void
destroy (T *ptr)
{
@ -150,14 +138,16 @@ namespace cruft {
}
//---------------------------------------------------------------------
void destroy (size_t idx)
{
return destroy (&(*this)[idx]);
}
///////////////////////////////////////////////////////////////////////
auto capacity (void) const { return m_capacity; }
auto size (void) const { return m_size.load (); }
auto size (void) const { return capacity () - m_available.size (); }
bool empty (void) const { return size () == 0; }
bool full (void) const { return size () == capacity (); }
@ -173,80 +163,44 @@ namespace cruft {
/// object for the duration of this call.
void clear (void)
{
// Create a fake root so that we can always point to the parent
// of every node in the system. Hopefully this isn't too large for
// the stack.
node container;
container.next.store (m_next.load ());
// Sort the node list. We walk the list, and at each step reparent
// the child at the lowest memory address to the cursor.
for (node* start = container.raw; start; start = start->raw) {
node* parent = start;
// Find the node whose child is the lowest pointer
int count = 0;
for (auto cursor = parent; cursor->raw; cursor = cursor->raw) {
++count;
CHECK_NEQ (cursor->raw, start);
if (cursor->raw < parent)
parent = cursor;
}
// Parent the lowest child to the start of the sorted list
auto tmp = start->raw;
start->raw = parent->raw;
// Remove the lowest child from their old parent
auto parent_next = parent->raw;
parent->raw = parent_next ? parent_next->raw : nullptr;
// Parent the old successor of the start to the lowest child
start->raw = tmp;
}
auto const valid_queue = m_available.store (
decltype(m_available)::contract::I_HAVE_LOCKED_THIS_STRUCTURE
);
std::sort (valid_queue.begin (), valid_queue.end ());
// Now that we've ordered the nodes we can walk the list from
// start to finish and find nodes that aren't in the free list.
// Call the destructors on the data contained in these.
auto node_cursor = m_next.load (std::memory_order_relaxed);
auto data_cursor = m_head;
auto node_cursor = valid_queue.begin ();
auto data_cursor = reinterpret_cast<T*> (m_store);
auto const data_end = data_cursor + m_capacity;
while (node_cursor) {
while (data_cursor < node_cursor) {
cruft::cast::alignment<T*> (data_cursor->data)->~T ();
while (node_cursor != valid_queue.end ()) {
while (&*data_cursor < *node_cursor) {
reinterpret_cast<T*> (&*data_cursor)->~T ();
++data_cursor;
}
node_cursor = node_cursor->raw;
++node_cursor;
++data_cursor;
}
while (data_cursor < m_head + m_capacity) {
cruft::cast::alignment<T*> (data_cursor->data)->~T ();
while (data_cursor != data_end) {
reinterpret_cast<T*> (&*data_cursor)->~T ();
++data_cursor;
}
relink ();
m_available.clear ();
T* elements = reinterpret_cast<T*> (m_store);
for (size_t i = 0; i < m_capacity; ++i)
m_available.push (elements + i);
}
private:
void relink (void)
{
// Reset the allocation cursor to point to the start of the region
m_next = m_head;
// build out the linked list from all the nodes.
for (size_t i = 0; i < m_capacity - 1; ++i)
m_next[i].next = m_next + i + 1;
m_next[m_capacity - 1].next = nullptr;
}
public:
// Indexing
///////////////////////////////////////////////////////////////////////
size_t index (T const *ptr) const
{
CHECK_LIMIT (cruft::cast::alignment<node const*> (ptr), m_head, m_head + m_capacity);
return cruft::cast::alignment<node const*> (ptr) - m_head;
return ptr - reinterpret_cast<T*> (m_store);
}
@ -255,22 +209,27 @@ namespace cruft {
/// guaranteed to point to the first _possible_ allocated value;
/// however it may not be _live_ at any given moment.
///
/// DO NOT use this pointer for indexing as you will be unable to
/// account for internal node sizes, alignment, or padding.
void * base (void) & { return m_head; }
void const* base (void) const& { return m_head; }
/// DO NOT use this pointer for indexing as you _may_ be unable to
/// account for internal node sizes, alignment, or padding. This is
/// why the return type is void.
///
/// We may be using one particular representation at the moment but
/// stability is not guaranteed at this point.
void * base (void) & { return m_store; }
void const* base (void) const& { return m_store; }
///////////////////////////////////////////////////////////////////////
T& operator[] (size_t idx) &
{
CHECK_LIMIT (idx, 0u, capacity ());
return *cruft::cast::alignment<T*> (&m_head[idx].data[0]);
return reinterpret_cast<T*> (m_store) [idx];
}
//---------------------------------------------------------------------
T const& operator[] (size_t idx) const&
{
CHECK_LIMIT (idx, 0u, capacity ());
return *cruft::cast::alignment<T const*> (&m_head[idx].data[0]);
return reinterpret_cast<T*> (m_store) [idx];
}
};
}