resourceToken.hpp

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/**
 * @file
 * @ingroup daq
 * @copyright (c) Copyright ESO 2023
 * All Rights Reserved
 * ESO (eso.org) is an Intergovernmental Organisation, and therefore special legal conditions apply.
 */
#ifndef DAQ_RESOURCE_TOKEN_HPP
#define DAQ_RESOURCE_TOKEN_HPP
 
#include <daq/config.hpp>
#include <optional>
#include <queue>
 
#include <boost/signals2.hpp>
#include <boost/thread/future.hpp>
 
namespace daq {
class Resource;
/**
 * RAII token
 */
class ResourceToken {
public:
    ResourceToken(Resource*) noexcept;
    ResourceToken(ResourceToken const&) = delete;
    ResourceToken& operator=(ResourceToken&) = delete;
 
    ResourceToken(ResourceToken&&) noexcept;
    ResourceToken& operator=(ResourceToken&&) noexcept;
 
    ~ResourceToken() noexcept;
 
private:
    Resource* m_resource;
};
 
class Resource {
public:
    /**
     * Signal that emits on changes to resources.
     */
    using Signal = boost::signals2::signal<void()>;
    Resource() = default;
    explicit Resource(unsigned limit) noexcept : m_limit(limit) {
    }
    Resource& operator=(Resource const&) noexcept = delete;
 
    boost::future<ResourceToken> AsyncAcquire() noexcept;
 
    std::optional<ResourceToken> Acquire() noexcept;
 
    bool HasResource() const noexcept {
        return m_limit == 0 || m_used < m_limit;
    }
 
    void SetLimit(unsigned new_limit) noexcept {
        m_limit = new_limit;
    }
    unsigned GetLimit() const noexcept {
        return m_limit;
    }
    unsigned GetUsed() const noexcept {
        return m_used;
    }
 
    /**
     * Connect to signal that is emitted when a resource become available.
     *
     * @note There's no guarantee that once signalled there are resources still available.
     */
    boost::signals2::connection Connect(Signal::slot_type const& slot);
 
protected:
    void Release() noexcept;
 
private:
    friend class ResourceToken;
    unsigned m_limit = 0;
    unsigned m_used = 0;
    Signal m_signal;
    std::queue<boost::promise<ResourceToken>> m_promises;
};
}  // namespace daq
#endif  // #ifndef DAQ_RESOURCE_TOKEN_HPP