There's a simple guide on the Firebase's website on how to implement the AdMob's rewarded video: https://firebase.google.com/docs/admob/unity/rewarded-video

Let's take some code:

public void OnVideoAdComplete(object sender, Reward reward){
    SoundMgr.Instance().PlayRewardSound();
    // double coins etc
}

Let's plug it in:

private void LoadVideoAd(){
    videoAd = RewardBasedVideoAd.Instance;

    AdRequest request = new AdRequest.Builder().AddTestDevice("XXXXXXXXXXXXX").Build();
    videoAd.LoadAd(request, androidVideoAdID);

    if(!videoCallbackSet){
        videoCallbackSet = true;
        videoAd.OnAdRewarded += OnVideoAdComplete;
    }
}

And now let's get a ThreadException cause we played a sound on the other thread:

Unity   : Function SoundChannelStopList::~SoundChannelStopList() may only be called from main thread!

Unity   : ExecutionEngineException: SIGILL
Unity   :   at SoundManager.PlaySuccess1Sound () [0x00000] in <filename unknown>:0
Unity   :   at Game.OnVideoAdClose () [0x00000] in <filename unknown>:0
Unity   :   at AdManager.OnVideoAdClose (System.Object sender, System.EventArgs args) [0x00000] in <filename unknown>:0
Unity   :   at GoogleMobileAds.Api.RewardBasedVideoAd.<RewardBasedVideoAd>m__4 (System.Object sender, System.EventArgs args) [0x00000] in <filename unknown>:0
Unity   :   at (wrapper delegate-invoke) 
System.EventHandler`1<System.EventArgs>:invoke_void__this___object_EventArgs (object,System.EventArgs)
Unity   :   at GoogleMobileAds.Android.RewardBasedVideoAdClient.onAdClosed () [0x00000] in <filename unknown>:0
Unity   :   at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
Unity   : Rethrow as TargetInvocationException: GoogleMobileAds.Android.RewardBasedVideoAdClient.onAdClosed()
Unity   :   at UnityEngine.AndroidJavaPro

How is this possible that it's year 2017 and the most leading game engine's plugin is runnning it's callbacks without some sort of App.PostRunnableOnMainThread()?

Is there any workaround on this or we need to create an incredible pattern like:

while(!adNotFinished)
    continue;

// then play sound

I'd be grateful for any tips! :)

There's a simple guide on the Firebase's website on how to implement the AdMob's rewarded video: https://firebase.google.com/docs/admob/unity/rewarded-video

Let's take some code:

public void OnVideoAdComplete(object sender, Reward reward){
    SoundMgr.Instance().PlayRewardSound();
    // double coins etc
}

Let's plug it in:

private void LoadVideoAd(){
    videoAd = RewardBasedVideoAd.Instance;

    AdRequest request = new AdRequest.Builder().AddTestDevice("XXXXXXXXXXXXX").Build();
    videoAd.LoadAd(request, androidVideoAdID);

    if(!videoCallbackSet){
        videoCallbackSet = true;
        videoAd.OnAdRewarded += OnVideoAdComplete;
    }
}

And now let's get a ThreadException cause we played a sound on the other thread:

Unity   : Function SoundChannelStopList::~SoundChannelStopList() may only be called from main thread!

Unity   : ExecutionEngineException: SIGILL
Unity   :   at SoundManager.PlaySuccess1Sound () [0x00000] in <filename unknown>:0
Unity   :   at Game.OnVideoAdClose () [0x00000] in <filename unknown>:0
Unity   :   at AdManager.OnVideoAdClose (System.Object sender, System.EventArgs args) [0x00000] in <filename unknown>:0
Unity   :   at GoogleMobileAds.Api.RewardBasedVideoAd.<RewardBasedVideoAd>m__4 (System.Object sender, System.EventArgs args) [0x00000] in <filename unknown>:0
Unity   :   at (wrapper delegate-invoke) 
System.EventHandler`1<System.EventArgs>:invoke_void__this___object_EventArgs (object,System.EventArgs)
Unity   :   at GoogleMobileAds.Android.RewardBasedVideoAdClient.onAdClosed () [0x00000] in <filename unknown>:0
Unity   :   at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
Unity   : Rethrow as TargetInvocationException: GoogleMobileAds.Android.RewardBasedVideoAdClient.onAdClosed()
Unity   :   at UnityEngine.AndroidJavaPro

How is this possible that it's year 2017 and the most leading game engine's plugin is runnning it's callbacks without some sort of App.PostRunnableOnMainThread()?

Is there any workaround on this or we need to create an incredible pattern like:

update(){
    if(adFinished)
        //give rewards
    }

I'd be grateful for any tips! :)