drivers/gpu/msd-vsl-gc/src/page_table_slot_allocator.h

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef PAGE_TABLE_SLOT_ALLOCATOR_H_
#define PAGE_TABLE_SLOT_ALLOCATOR_H_

#include "magma_util/macros.h"
#include <atomic>
#include <mutex>
#include <vector>

// Thread-safe.
class PageTableSlotAllocator {
public:
    PageTableSlotAllocator(uint32_t size) : slot_busy_(size), next_index_(size - 1) {}

    uint32_t size() { return slot_busy_.size(); }

    bool Alloc(uint32_t* index_out)
    {
        std::lock_guard<std::mutex> lock(mutex_);
        for (uint32_t i = 0; i < slot_busy_.size(); i++) {
            uint32_t index = (next_index_ + i) % slot_busy_.size();
            if (!slot_busy_[index]) {
                slot_busy_[index] = true;
                *index_out = index;
                next_index_ = index + 1;
                return true;
            }
        }
        return false;
    }

    // Called on the connection thread.
    void Free(uint32_t index)
    {
        DASSERT(index < slot_busy_.size());
        DASSERT(slot_busy_[index]);
        slot_busy_[index] = false;
    }

private:
    std::vector<std::atomic<bool>> slot_busy_;
    std::mutex mutex_;
    uint32_t next_index_;

    friend class TestPageTableSlotAllocator;
};

#endif // PAGE_TABLE_SLOT_ALLOCATOR_H_