90 lines
2.7 KiB
C++
90 lines
2.7 KiB
C++
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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2019 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include "../thread/primitive.hpp"
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#include "../debug/assert.hpp"
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#include "../thread/spinlock.hpp"
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#include <atomic>
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#include <vector>
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#include <mutex>
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#include <cstddef>
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namespace cruft::parallel {
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/// A trivial thread safe stack with a fixed capacity.
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///
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/// This implementation uses a spinlock, so don't try to push large
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/// objects under high contention. In the future it may be replaced with a
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/// different locking mechanism.
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template <typename ValueT>
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class stack {
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public:
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stack (std::size_t capacity)
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: m_cursor (0)
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, m_store (capacity)
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{
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CHECK_GT (capacity, 0u);
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}
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/// Move the value from the top of the stack into an output pointer.
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///
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/// The internal object will be destroyed after the output has been set.
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///
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/// The value `true` will be returned if the value was successfully
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/// copied. If no object is available for popping, or locking failed,
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/// the value `false` will be returned.
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///
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/// NOTE: There are no exception guarantees at this time.
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bool pop (ValueT *out)
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{
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std::lock_guard lk (m_lock);
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if (m_cursor == 0)
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return false;
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auto ptr = reinterpret_cast<ValueT*> (&m_store[--m_cursor]);
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*out = std::move (*ptr);
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ptr->~ValueT ();
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return true;
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}
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/// Constructs a ValueT on the top of the stack.
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///
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/// The value `true` will be returned if the object was successfully
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/// stored. In the event of a lack of capacity, locking failure, or
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/// other error the value `false` will be returned and the user may
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/// retry the operation.
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///
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/// NOTE: There are no exception guarantees at this time.
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template <typename InputT>
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bool push (InputT &&arg)
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{
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std::lock_guard lk (m_lock);
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if (m_cursor >= m_store.size ())
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return false;
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auto ptr = reinterpret_cast<ValueT *> (&m_store[m_cursor++]);
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new (ptr) ValueT (std::forward<InputT> (arg));
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return true;
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}
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private:
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using index_type = std::size_t;
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using raw_type = std::aligned_storage_t<sizeof(ValueT), alignof(ValueT)>;
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cruft::thread::spinlock m_lock;
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std::atomic<index_type> m_cursor;
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std::vector<raw_type> m_store;
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};
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}
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