/// A borrowed execution context (+ its bound profile). Returns the context to the pool

/// on destruction. Move-only.

class Lease {

public:

Lease() = default;

Lease(Lease &&other) noexcept;

Lease &operator=(Lease &&other) noexcept;

Lease(const Lease &) = delete;

Lease &operator=(const Lease &) = delete;

~Lease();

bool valid() const noexcept { return slot_ >= 0; }

int profileIndex() const noexcept { return profile_; }

/// Caller-allocated, zero-copy (mirrors Engine::enqueue) on this lease's context+profile.

Status enqueue(const std::unordered_map<std::string, TensorView> &inputs,

const std::unordered_map<std::string, TensorView> &outputs, const Stream &stream);

/// Library-allocated convenience (mirrors Engine::infer).

Result<std::unordered_map<std::string, Tensor>> infer(const std::unordered_map<std::string, TensorView> &inputs,

const Stream &stream);

Result<Tensor> inferSingle(const std::unordered_map<std::string, TensorView> &inputs, const Stream &stream);

Result<std::unordered_map<std::string, Shape>> outputShapes(const std::unordered_map<std::string, TensorView> &inputs);

private:

friend class EnginePool;

Lease(std::shared_ptr<detail::PoolState> state, int slot, int profile) : state_(std::move(state)), slot_(slot), profile_(profile) {}

std::shared_ptr<detail::PoolState> state_;

int slot_ = -1;

int profile_ = 0;

};

EnginePool(EnginePool &&) noexcept;

EnginePool &operator=(EnginePool &&) noexcept;

EnginePool(const EnginePool &) = delete;

EnginePool &operator=(const EnginePool &) = delete;

~EnginePool();

static Result<EnginePool> create(const std::string &enginePath, int contexts, const EngineOptions &options = {});

Result<Lease> acquire(); ///< blocks until a context is free

std::optional<Lease> tryAcquire(); ///< returns nullopt if none free

int size() const noexcept; ///< number of contexts (== profiles for dynamic engines)

std::vector<TensorInfo> tensors() const;

std::vector<std::string> inputNames() const;

std::vector<std::string> outputNames() const;

EnginePool() = default;

std::shared_ptr<detail::PoolState> state_;