library/cpp/messagebus/async_result.h


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#pragma once 
 
#include <util/generic/maybe.h> 
#include <util/generic/noncopyable.h> 
#include <util/system/condvar.h>
#include <util/system/mutex.h>
#include <util/system/yassert.h>

#include <functional>
 
// probably this thing should have been called TFuture 
template <typename T> 
class TAsyncResult : TNonCopyable { 
private: 
    TMutex Mutex; 
    TCondVar CondVar; 
 
    TMaybe<T> Result; 
 
    typedef void TOnResult(const T&); 
 
    std::function<TOnResult> OnResult;
 
public: 
    void SetResult(const T& result) { 
        TGuard<TMutex> guard(Mutex); 
        Y_VERIFY(!Result, "cannot set result twice");
        Result = result; 
        CondVar.BroadCast(); 
 
        if (!!OnResult) { 
            OnResult(result); 
        } 
    } 
 
    const T& GetResult() { 
        TGuard<TMutex> guard(Mutex); 
        while (!Result) { 
            CondVar.Wait(Mutex); 
        } 
        return *Result; 
    } 
 
    template <typename TFunc> 
    void AndThen(const TFunc& onResult) {
        TGuard<TMutex> guard(Mutex); 
        if (!!Result) { 
            onResult(*Result); 
        } else { 
            Y_ASSERT(!OnResult);
            OnResult = std::function<TOnResult>(onResult);
        } 
    } 
};