src/main.rs

@@ -26,7 +26,7 @@ use musichoard::{
 };
 
 use tui::{
-    App, EventChannel, EventHandler, EventListener, JobChannel, MusicBrainz, MusicBrainzDaemon,
+    App, EventChannel, EventHandler, EventListener, MusicBrainz, MusicBrainzDaemon, RequestChannel,
     Tui, Ui,
 };
 
@@ -94,13 +94,13 @@ fn with<Database: IDatabase + 'static, Library: ILibrary + 'static>(
     let listener = EventListener::new(listener_sender);
     let handler = EventHandler::new(channel.receiver());
 
-    let mb_job_channel = JobChannel::new();
+    let mb_request_channel = RequestChannel::new();
+    thread::spawn(|| MusicBrainzDaemon::run(musicbrainz, mb_request_channel.receiver, app_sender));
 
-    let app = App::new(music_hoard, mb_job_channel.sender());
+    let app = App::new(music_hoard, mb_request_channel.sender);
     let ui = Ui;
 
     // Run the TUI application.
-    thread::spawn(|| MusicBrainzDaemon::run(musicbrainz, mb_job_channel.receiver(), app_sender));
     Tui::run(terminal, app, ui, handler, listener).expect("failed to run tui");
 }
 

src/tui/app/machine/fetch_state.rs

@@ -1,17 +1,18 @@
-use std::{
-    collections::VecDeque,
-    sync::mpsc::{self, TryRecvError},
-};
+use std::{collections::VecDeque, sync::mpsc::{self, TryRecvError}};
 
 use musichoard::collection::{artist::Artist, musicbrainz::IMusicBrainzRef};
 
 use crate::tui::{
     app::{
         machine::{match_state::MatchState, App, AppInner, AppMachine},
-        AppPublicState, AppState, IAppEventFetch, IAppInteractFetch,
+        AppPublicState, AppState, IAppEventFetch, IAppInteractFetch, MatchStateInfo,
     },
-    lib::external::musicbrainz::daemon::{
-        Error as DaemonError, IMbJobSender, MbApiResult, MbParams, ResultSender,
+    lib::{
+        external::musicbrainz::daemon::{
+            ApiParams, Job, JobInstance, JobPriority, ReturnSender, SearchArtistParams,
+            SearchParams, SearchReleaseGroupParams,
+        },
+        interface::musicbrainz::api::Error as MbError,
     },
 };
 
@@ -19,13 +20,16 @@ pub struct FetchState {
     fetch_rx: FetchReceiver,
 }
 
-pub type FetchReceiver = mpsc::Receiver<MbApiResult>;
 impl FetchState {
     pub fn new(fetch_rx: FetchReceiver) -> Self {
         FetchState { fetch_rx }
     }
 }
 
+pub type FetchError = MbError;
+pub type FetchResult = Result<MatchStateInfo, FetchError>;
+pub type FetchReceiver = mpsc::Receiver<FetchResult>;
+
 impl AppMachine<FetchState> {
     fn fetch_state(inner: AppInner, state: FetchState) -> Self {
         AppMachine::new(inner, state)
@@ -40,10 +44,8 @@ impl AppMachine<FetchState> {
             }
         };
 
-        let (fetch_tx, fetch_rx) = mpsc::channel::<MbApiResult>();
-        if let Err(err) = Self::submit_fetch_job(&inner.musicbrainz, fetch_tx, artist) {
-            return AppMachine::error_state(inner, err.to_string()).into();
-        }
+        let (fetch_tx, fetch_rx) = mpsc::channel::<FetchResult>();
+        Self::submit_fetch_job(&inner, artist, fetch_tx);
 
         let fetch = FetchState::new(fetch_rx);
         AppMachine::app_fetch(inner, fetch, true)
@@ -77,22 +79,25 @@ impl AppMachine<FetchState> {
         }
     }
 
-    fn submit_fetch_job(
-        musicbrainz: &Box<dyn IMbJobSender>,
-        result_sender: ResultSender,
-        artist: &Artist,
-    ) -> Result<(), DaemonError> {
-        let requests = match artist.meta.musicbrainz {
+    fn submit_fetch_job(inner: &AppInner, artist: &Artist, tx: ReturnSender) {
+        let mut queue = VecDeque::new();
+        match artist.meta.musicbrainz {
             Some(ref arid) => {
-                let arid = arid.mbid();
-                let albums = artist.albums.iter();
-                albums
-                    .map(|album| MbParams::search_release_group(arid.clone(), album.meta.clone()))
-                    .collect()
+                let arid = arid.mbid().clone();
+                for album in artist.albums.iter() {
+                    queue.push_back(ApiParams::search(SearchParams::release_group(
+                        SearchReleaseGroupParams::new(arid.clone(), album.meta.clone()),
+                    )));
                 }
-            None => VecDeque::from([MbParams::search_artist(artist.meta.clone())]),
-        };
-        musicbrainz.submit_background_job(result_sender, requests)
+            }
+            None => {
+                queue.push_back(ApiParams::search(SearchParams::artist(
+                    SearchArtistParams::new(artist.meta.clone()),
+                )));
+            }
+        }
+        let job = Job::new(JobPriority::Background, JobInstance::new(tx, queue));
+        inner.musicbrainz.send(job);
     }
 }
 

src/tui/app/machine/mod.rs

@@ -8,12 +8,14 @@ mod match_state;
 mod reload_state;
 mod search_state;
 
+use std::sync::mpsc;
+
 use crate::tui::{
     app::{
         selection::Selection, AppMode, AppPublic, AppPublicInner, AppPublicState, AppState, IApp,
         IAppAccess, IAppBase, IAppState,
     },
-    lib::{external::musicbrainz::daemon::IMbJobSender, IMusicHoard},
+    lib::{external::musicbrainz::daemon::Job, IMusicHoard},
 };
 
 use browse_state::BrowseState;
@@ -46,7 +48,7 @@ pub struct AppMachine<STATE> {
 pub struct AppInner {
     running: bool,
     music_hoard: Box<dyn IMusicHoard>,
-    musicbrainz: Box<dyn IMbJobSender>,
+    musicbrainz: mpsc::Sender<Job>,
     selection: Selection,
 }
 
@@ -81,9 +83,9 @@ macro_rules! app_field_mut {
 }
 
 impl App {
-    pub fn new<MH: IMusicHoard + 'static, MB: IMbJobSender + 'static>(
+    pub fn new<MH: IMusicHoard + 'static>(
         mut music_hoard: MH,
-        musicbrainz: MB,
+        musicbrainz: mpsc::Sender<Job>,
     ) -> Self {
         let init_result = Self::init(&mut music_hoard);
         let inner = AppInner::new(music_hoard, musicbrainz);
@@ -169,15 +171,12 @@ impl IAppAccess for App {
 }
 
 impl AppInner {
-    pub fn new<MH: IMusicHoard + 'static, MB: IMbJobSender + 'static>(
-        music_hoard: MH,
-        musicbrainz: MB,
-    ) -> Self {
+    pub fn new<MH: IMusicHoard + 'static>(music_hoard: MH, musicbrainz: mpsc::Sender<Job>) -> Self {
         let selection = Selection::new(music_hoard.get_collection());
         AppInner {
             running: true,
             music_hoard: Box::new(music_hoard),
-            musicbrainz: Box::new(musicbrainz),
+            musicbrainz,
             selection,
         }
     }

src/tui/event.rs

@@ -42,7 +42,7 @@ impl From<mpsc::TryRecvError> for EventError {
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Event {
     Key(KeyEvent),
-    FetchComplete,
+    FetchResultReady,
 }
 
 pub struct EventChannel {
@@ -50,14 +50,6 @@ pub struct EventChannel {
     receiver: mpsc::Receiver<Event>,
 }
 
-pub trait IKeyEventSender {
-    fn send_key(&self, key_event: KeyEvent) -> Result<(), EventError>;
-}
-
-pub trait IFetchCompleteEventSender {
-    fn send_fetch_complete(&self) -> Result<(), EventError>;
-}
-
 #[derive(Clone)]
 pub struct EventSender {
     sender: mpsc::Sender<Event>,
@@ -86,15 +78,9 @@ impl EventChannel {
     }
 }
 
-impl IKeyEventSender for EventSender {
-    fn send_key(&self, key_event: KeyEvent) -> Result<(), EventError> {
-        Ok(self.sender.send(Event::Key(key_event))?)
-    }
-}
-
-impl IFetchCompleteEventSender for EventSender {
-    fn send_fetch_complete(&self) -> Result<(), EventError> {
-        Ok(self.sender.send(Event::FetchComplete)?)
+impl EventSender {
+    pub fn send(&self, event: Event) -> Result<(), EventError> {
+        Ok(self.sender.send(event)?)
     }
 }
 
@@ -122,13 +108,13 @@ mod tests {
         let channel = EventChannel::new();
         let sender = channel.sender();
         let receiver = channel.receiver();
-        let key_event = KeyEvent::new(KeyCode::Up, KeyModifiers::empty());
+        let event = Event::Key(KeyEvent::new(KeyCode::Up, KeyModifiers::empty()));
 
-        let result = sender.send_key(key_event);
+        let result = sender.send(event);
         assert!(result.is_ok());
 
         drop(receiver);
-        let result = sender.send_key(key_event);
+        let result = sender.send(event);
         assert!(result.is_err());
     }
 
@@ -137,9 +123,9 @@ mod tests {
         let channel = EventChannel::new();
         let sender = channel.sender();
         let receiver = channel.receiver();
-        let key_event = KeyEvent::new(KeyCode::Up, KeyModifiers::empty());
+        let event = Event::Key(KeyEvent::new(KeyCode::Up, KeyModifiers::empty()));
 
-        sender.send_key(key_event).unwrap();
+        sender.send(event).unwrap();
         let result = receiver.recv();
         assert!(result.is_ok());
 
@@ -153,11 +139,12 @@ mod tests {
         let channel = EventChannel::new();
         let sender = channel.sender();
         let receiver = channel.receiver();
+        let event = Event::FetchResultReady;
 
         let result = receiver.try_recv();
         assert!(result.is_err());
 
-        sender.send_fetch_complete().unwrap();
+        sender.send(event).unwrap();
         let result = receiver.try_recv();
         assert!(result.is_ok());
 

src/tui/handler.rs

@@ -28,7 +28,7 @@ trait IEventHandlerPrivate<APP: IApp> {
     fn handle_error_key_event(app: <APP as IApp>::ErrorState, key_event: KeyEvent) -> APP;
     fn handle_critical_key_event(app: <APP as IApp>::CriticalState, key_event: KeyEvent) -> APP;
 
-    fn handle_fetch_complete_event(app: APP) -> APP;
+    fn handle_fetch_result_ready_event(app: APP) -> APP;
 
     fn handle_input_key_event<Input: IAppInput<APP = APP>>(app: Input, key_event: KeyEvent) -> APP;
 }
@@ -48,7 +48,7 @@ impl<APP: IApp> IEventHandler<APP> for EventHandler {
     fn handle_next_event(&self, app: APP) -> Result<APP, EventError> {
         Ok(match self.events.recv()? {
             Event::Key(key_event) => Self::handle_key_event(app, key_event),
-            Event::FetchComplete => Self::handle_fetch_complete_event(app),
+            Event::FetchResultReady => Self::handle_fetch_result_ready_event(app),
         })
     }
 }
@@ -92,7 +92,7 @@ impl<APP: IApp> IEventHandlerPrivate<APP> for EventHandler {
         }
     }
 
-    fn handle_fetch_complete_event(app: APP) -> APP {
+    fn handle_fetch_result_ready_event(app: APP) -> APP {
         match app.state() {
             AppState::Browse(state) => state.no_op(),
             AppState::Info(state) => state.no_op(),

src/tui/lib/external/musicbrainz/daemon/mod.rs

@@ -1,37 +1,35 @@
-use std::{collections::VecDeque, fmt, sync::mpsc, thread, time};
+use std::{collections::VecDeque, sync::mpsc, thread, time};
 
 use musichoard::collection::{album::AlbumMeta, artist::ArtistMeta, musicbrainz::Mbid};
 
 use crate::tui::{
     app::MatchStateInfo,
-    event::IFetchCompleteEventSender,
+    event::{Event, EventSender},
     lib::interface::musicbrainz::api::{Error as ApiError, IMusicBrainz},
 };
 
 pub enum Error {
-    EventChannelDisconnected,
-    JobChannelDisconnected,
+    RequestRecv(String),
+    Api(String),
 }
 
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            Error::EventChannelDisconnected => write!(f, "the event channel is disconnected"),
-            Error::JobChannelDisconnected => write!(f, "the job channel is disconnected"),
+impl From<mpsc::RecvError> for Error {
+    fn from(value: mpsc::RecvError) -> Self {
+        Error::RequestRecv(value.to_string())
     }
 }
+
+impl From<ApiError> for Error {
+    fn from(value: ApiError) -> Self {
+        Error::Api(value.to_string())
+    }
 }
 
 pub struct MusicBrainzDaemon {
-    musicbrainz: Box<dyn IMusicBrainz>,
-    job_receiver: mpsc::Receiver<Job>,
+    api: Box<dyn IMusicBrainz>,
+    request_receiver: mpsc::Receiver<Job>,
     job_queue: JobQueue,
-    event_sender: Box<dyn IFetchCompleteEventSender>,
-}
-
-enum JobError {
-    JobQueueEmpty,
-    EventChannelDisconnected,
+    events: EventSender,
 }
 
 struct JobQueue {
@@ -39,286 +37,6 @@ struct JobQueue {
     background_queue: VecDeque<JobInstance>,
 }
 
-struct Job {
-    priority: JobPriority,
-    instance: JobInstance,
-}
-
-impl Job {
-    pub fn new(priority: JobPriority, instance: JobInstance) -> Self {
-        Job { priority, instance }
-    }
-}
-
-enum JobPriority {
-    Foreground,
-    Background,
-}
-
-pub type MbApiResult = Result<MatchStateInfo, ApiError>;
-pub type ResultSender = mpsc::Sender<MbApiResult>;
-struct JobInstance {
-    result_sender: ResultSender,
-    requests: VecDeque<MbParams>,
-}
-
-enum JobInstanceStatus {
-    Continue,
-    Complete,
-}
-
-enum JobInstanceError {
-    ReturnChannelDisconnected,
-    EventChannelDisconnected,
-}
-
-impl JobInstance {
-    fn new(result_sender: ResultSender, requests: VecDeque<MbParams>) -> Self {
-        JobInstance {
-            result_sender,
-            requests,
-        }
-    }
-}
-
-pub enum MbParams {
-    Search(SearchParams),
-}
-
-impl MbParams {
-    pub fn search_artist(artist: ArtistMeta) -> Self {
-        MbParams::Search(SearchParams::Artist(SearchArtistParams { artist }))
-    }
-
-    pub fn search_release_group(arid: Mbid, album: AlbumMeta) -> Self {
-        MbParams::Search(SearchParams::ReleaseGroup(SearchReleaseGroupParams {
-            arid,
-            album,
-        }))
-    }
-}
-
-pub enum SearchParams {
-    Artist(SearchArtistParams),
-    ReleaseGroup(SearchReleaseGroupParams),
-}
-
-pub struct SearchArtistParams {
-    artist: ArtistMeta,
-}
-
-pub struct SearchReleaseGroupParams {
-    arid: Mbid,
-    album: AlbumMeta,
-}
-
-pub struct JobChannel {
-    sender: mpsc::Sender<Job>,
-    receiver: mpsc::Receiver<Job>,
-}
-
-pub struct JobSender {
-    sender: mpsc::Sender<Job>,
-}
-
-pub struct JobReceiver {
-    receiver: mpsc::Receiver<Job>,
-}
-
-impl JobChannel {
-    pub fn new() -> Self {
-        let (sender, receiver) = mpsc::channel();
-        JobChannel { receiver, sender }
-    }
-
-    pub fn sender(&self) -> JobSender {
-        JobSender {
-            sender: self.sender.clone(),
-        }
-    }
-
-    pub fn receiver(self) -> JobReceiver {
-        JobReceiver {
-            receiver: self.receiver,
-        }
-    }
-}
-
-pub trait IMbJobSender {
-    fn submit_background_job(
-        &self,
-        result_sender: ResultSender,
-        requests: VecDeque<MbParams>,
-    ) -> Result<(), Error>;
-}
-
-impl IMbJobSender for JobSender {
-    fn submit_background_job(
-        &self,
-        result_sender: ResultSender,
-        requests: VecDeque<MbParams>,
-    ) -> Result<(), Error> {
-        self.send_background_job(result_sender, requests)
-    }
-}
-
-impl JobSender {
-    fn send_background_job(
-        &self,
-        result_sender: ResultSender,
-        requests: VecDeque<MbParams>,
-    ) -> Result<(), Error> {
-        self.send_job(JobPriority::Background, result_sender, requests)
-    }
-
-    fn send_job(
-        &self,
-        priority: JobPriority,
-        result_sender: ResultSender,
-        requests: VecDeque<MbParams>,
-    ) -> Result<(), Error> {
-        let instance = JobInstance::new(result_sender, requests);
-        let job = Job::new(priority, instance);
-        self.sender.send(job).or(Err(Error::JobChannelDisconnected))
-    }
-}
-
-impl MusicBrainzDaemon {
-    pub fn run<MB: IMusicBrainz + 'static, ES: IFetchCompleteEventSender + 'static>(
-        musicbrainz: MB,
-        job_receiver: JobReceiver,
-        event_sender: ES,
-    ) -> Result<(), Error> {
-        let daemon = MusicBrainzDaemon {
-            musicbrainz: Box::new(musicbrainz),
-            job_receiver: job_receiver.receiver,
-            job_queue: JobQueue::new(),
-            event_sender: Box::new(event_sender),
-        };
-        daemon.main()
-    }
-
-    fn main(mut self) -> Result<(), Error> {
-        loop {
-            self.enqueue_all_pending_jobs()?;
-            match self.execute_next_job() {
-                Ok(()) => {
-                    // Sleep for one second. Required by MB API rate limiting. Assume all other
-                    // processing takes negligible time such that regardless of how much other
-                    // processing there is to be done, this one second sleep is necessary.
-                    thread::sleep(time::Duration::from_secs(1));
-                }
-                Err(JobError::JobQueueEmpty) => {
-                    self.wait_for_jobs()?;
-                }
-                Err(JobError::EventChannelDisconnected) => {
-                    return Err(Error::EventChannelDisconnected);
-                }
-            }
-        }
-    }
-
-    fn enqueue_all_pending_jobs(&mut self) -> Result<(), Error> {
-        loop {
-            match self.job_receiver.try_recv() {
-                Ok(job) => self.job_queue.push_back(job),
-                Err(mpsc::TryRecvError::Empty) => return Ok(()),
-                Err(mpsc::TryRecvError::Disconnected) => {
-                    return Err(Error::JobChannelDisconnected);
-                }
-            }
-        }
-    }
-
-    fn execute_next_job(&mut self) -> Result<(), JobError> {
-        if let Some(instance) = self.job_queue.front_mut() {
-            let result = instance.execute_next(&mut self.musicbrainz, &mut self.event_sender);
-            match result {
-                Ok(JobInstanceStatus::Continue) => {}
-                Ok(JobInstanceStatus::Complete)
-                | Err(JobInstanceError::ReturnChannelDisconnected) => {
-                    self.job_queue.pop_front();
-                }
-                Err(JobInstanceError::EventChannelDisconnected) => {
-                    return Err(JobError::EventChannelDisconnected)
-                }
-            }
-            return Ok(());
-        }
-        Err(JobError::JobQueueEmpty)
-    }
-
-    fn wait_for_jobs(&mut self) -> Result<(), Error> {
-        assert!(self.job_queue.is_empty());
-
-        match self.job_receiver.recv() {
-            Ok(job) => self.job_queue.push_back(job),
-            Err(mpsc::RecvError) => return Err(Error::JobChannelDisconnected),
-        }
-
-        Ok(())
-    }
-}
-
-impl JobInstance {
-    fn execute_next(
-        &mut self,
-        musicbrainz: &mut Box<dyn IMusicBrainz>,
-        event_sender: &mut Box<dyn IFetchCompleteEventSender>,
-    ) -> Result<JobInstanceStatus, JobInstanceError> {
-        // self.requests can be empty if the caller submits an empty job.
-        if let Some(params) = self.requests.pop_front() {
-            self.execute(musicbrainz, event_sender, params)?
-        }
-
-        if self.requests.is_empty() {
-            Ok(JobInstanceStatus::Complete)
-        } else {
-            Ok(JobInstanceStatus::Continue)
-        }
-    }
-
-    fn execute(
-        &mut self,
-        musicbrainz: &mut Box<dyn IMusicBrainz>,
-        event_sender: &mut Box<dyn IFetchCompleteEventSender>,
-        api_params: MbParams,
-    ) -> Result<(), JobInstanceError> {
-        match api_params {
-            MbParams::Search(search) => match search {
-                SearchParams::Artist(params) => {
-                    let result = musicbrainz.search_artist(&params.artist);
-                    let result = result.map(|list| MatchStateInfo::artist(params.artist, list));
-                    self.return_result(event_sender, result)
-                }
-                SearchParams::ReleaseGroup(params) => {
-                    let result = musicbrainz.search_release_group(&params.arid, &params.album);
-                    let result = result.map(|list| MatchStateInfo::album(params.album, list));
-                    self.return_result(event_sender, result)
-                }
-            },
-        }
-    }
-
-    fn return_result(
-        &mut self,
-        event_sender: &mut Box<dyn IFetchCompleteEventSender>,
-        result: Result<MatchStateInfo, ApiError>,
-    ) -> Result<(), JobInstanceError> {
-        self.result_sender
-            .send(result)
-            .map_err(|_| JobInstanceError::ReturnChannelDisconnected)?;
-
-        // If this send fails the event listener is dead. Don't panic as this function runs in a
-        // detached thread so this might be happening during normal shut down.
-        event_sender
-            .send_fetch_complete()
-            .map_err(|_| JobInstanceError::EventChannelDisconnected)?;
-
-        Ok(())
-    }
-}
-
 impl JobQueue {
     fn new() -> Self {
         JobQueue {
@@ -350,3 +68,207 @@ impl JobQueue {
         }
     }
 }
+
+pub struct Job {
+    priority: JobPriority,
+    instance: JobInstance,
+}
+
+impl Job {
+    pub fn new(priority: JobPriority, instance: JobInstance) -> Self {
+        Job { priority, instance }
+    }
+}
+
+pub enum JobPriority {
+    Foreground,
+    Background,
+}
+
+pub type ReturnSender = mpsc::Sender<Result<MatchStateInfo, ApiError>>;
+pub struct JobInstance {
+    return_sender: ReturnSender,
+    call_queue: VecDeque<ApiParams>,
+}
+
+impl JobInstance {
+    pub fn new(return_sender: ReturnSender, call_queue: VecDeque<ApiParams>) -> Self {
+        JobInstance {
+            return_sender,
+            call_queue,
+        }
+    }
+}
+
+pub enum ApiParams {
+    Search(SearchParams),
+}
+
+impl ApiParams {
+    pub fn search(params: SearchParams) -> Self {
+        ApiParams::Search(params)
+    }
+}
+
+pub enum SearchParams {
+    Artist(SearchArtistParams),
+    ReleaseGroup(SearchReleaseGroupParams),
+}
+
+impl SearchParams {
+    pub fn artist(params: SearchArtistParams) -> Self {
+        SearchParams::Artist(params)
+    }
+
+    pub fn release_group(params: SearchReleaseGroupParams) -> Self {
+        SearchParams::ReleaseGroup(params)
+    }
+}
+
+pub struct SearchArtistParams {
+    artist: ArtistMeta,
+}
+
+impl SearchArtistParams {
+    pub fn new(artist: ArtistMeta) -> Self {
+        SearchArtistParams { artist }
+    }
+}
+
+pub struct SearchReleaseGroupParams {
+    arid: Mbid,
+    album: AlbumMeta,
+}
+
+impl SearchReleaseGroupParams {
+    pub fn new(arid: Mbid, album: AlbumMeta) -> Self {
+        SearchReleaseGroupParams { arid, album }
+    }
+}
+
+pub struct RequestChannel {
+    pub receiver: mpsc::Receiver<Job>,
+    pub sender: mpsc::Sender<Job>,
+}
+
+impl RequestChannel {
+    pub fn new() -> Self {
+        let (sender, receiver) = mpsc::channel();
+        RequestChannel { receiver, sender }
+    }
+}
+
+impl MusicBrainzDaemon {
+    pub fn run<MB: IMusicBrainz + 'static>(
+        api: MB,
+        request_receiver: mpsc::Receiver<Job>,
+        events: EventSender,
+    ) -> Result<(), Error> {
+        let daemon = MusicBrainzDaemon {
+            api: Box::new(api),
+            request_receiver,
+            job_queue: JobQueue::new(),
+            events,
+        };
+        daemon.main()
+    }
+
+    fn wait_for_jobs(&mut self) -> Result<(), Error> {
+        if self.job_queue.is_empty() {
+            self.job_queue.push_back(self.request_receiver.recv()?);
+        }
+        Ok(())
+    }
+
+    fn enqueue_all_pending_jobs(&mut self) -> Result<(), Error> {
+        loop {
+            match self.request_receiver.try_recv() {
+                Ok(job) => self.job_queue.push_back(job),
+                Err(mpsc::TryRecvError::Empty) => return Ok(()),
+                Err(mpsc::TryRecvError::Disconnected) => {
+                    return Err(Error::RequestRecv(
+                        mpsc::TryRecvError::Disconnected.to_string(),
+                    ))
+                }
+            }
+        }
+    }
+
+    fn execute_next_job(&mut self) -> Option<()> {
+        if let Some(instance) = self.job_queue.front_mut() {
+            let result = instance.execute_next(&mut self.api, &mut self.events);
+            if result.is_none() {
+                self.job_queue.pop_front();
+            }
+            return Some(());
+        }
+        None
+    }
+
+    fn main(mut self) -> Result<(), Error> {
+        loop {
+            self.wait_for_jobs()?;
+            self.enqueue_all_pending_jobs()?;
+            if let Some(()) = self.execute_next_job() {
+                // Sleep for one second. Required by MB API rate limiting. Assume all other
+                // processing takes negligible time such that regardless of how much other
+                // processing there is to be done, this one second sleep is necessary.
+                thread::sleep(time::Duration::from_secs(1));
+            }
+        }
+    }
+}
+
+impl JobInstance {
+    fn execute_next(
+        &mut self,
+        api: &mut Box<dyn IMusicBrainz>,
+        events: &mut EventSender,
+    ) -> Option<()> {
+        self.call_queue
+            .pop_front()
+            .map(|api_params| self.execute_call(api, events, api_params));
+        if !self.call_queue.is_empty() {
+            Some(())
+        } else {
+            None
+        }
+    }
+
+    fn execute_call(
+        &mut self,
+        api: &mut Box<dyn IMusicBrainz>,
+        events: &mut EventSender,
+        api_params: ApiParams,
+    ) {
+        match api_params {
+            ApiParams::Search(search) => match search {
+                SearchParams::Artist(params) => {
+                    let result = api.search_artist(&params.artist);
+                    let result = result.map(|list| MatchStateInfo::artist(params.artist, list));
+                    self.return_result(events, result).ok();
+                }
+                SearchParams::ReleaseGroup(params) => {
+                    let result = api.search_release_group(&params.arid, &params.album);
+                    let result = result.map(|list| MatchStateInfo::album(params.album, list));
+                    self.return_result(events, result).ok();
+                }
+            },
+        }
+    }
+
+    fn return_result(
+        &mut self,
+        events: &mut EventSender,
+        result: Result<MatchStateInfo, ApiError>,
+    ) -> Result<(), ()> {
+        // If receiver disconnects just drop the rest.
+        self.return_sender.send(result).map_err(|_| ())?;
+
+        // If this send fails the event listener is dead. Don't panic as this function runs in a
+        // detached thread so this might be happening during normal shut down.
+        events.send(Event::FetchResultReady).map_err(|_| ())?;
+
+        Ok(())
+    }
+}

src/tui/listener.rs

@@ -4,7 +4,7 @@ use std::thread;
 #[cfg(test)]
 use mockall::automock;
 
-use crate::tui::event::{EventError, IKeyEventSender};
+use crate::tui::event::{Event, EventError, EventSender};
 
 #[cfg_attr(test, automock)]
 pub trait IEventListener {
@@ -12,15 +12,13 @@ pub trait IEventListener {
 }
 
 pub struct EventListener {
-    event_sender: Box<dyn IKeyEventSender + Send>,
+    events: EventSender,
 }
 
 // GRCOV_EXCL_START
 impl EventListener {
-    pub fn new<ES: IKeyEventSender + Send + 'static>(event_sender: ES) -> Self {
-        EventListener {
-            event_sender: Box::new(event_sender),
-        }
+    pub fn new(events: EventSender) -> Self {
+        EventListener { events }
     }
 }
 
@@ -34,7 +32,7 @@ impl IEventListener for EventListener {
                 match event::read() {
                     Ok(event) => {
                         if let Err(err) = match event {
-                            CrosstermEvent::Key(e) => self.event_sender.send_key(e),
+                            CrosstermEvent::Key(e) => self.events.send(Event::Key(e)),
                             _ => Ok(()),
                         } {
                             return err;

src/tui/mod.rs

@@ -10,7 +10,7 @@ pub use event::EventChannel;
 pub use handler::EventHandler;
 pub use lib::external::musicbrainz::{
     api::MusicBrainz,
-    daemon::{JobChannel, MusicBrainzDaemon},
+    daemon::{MusicBrainzDaemon, RequestChannel},
 };
 pub use listener::EventListener;
 pub use ui::Ui;