Synchronously decode images if decoded bytes are requested after the full response is received.

components/net/image_cache_thread.rs

@@ -57,7 +57,7 @@ fn is_image_opaque(format: webrender_traits::ImageFormat, bytes: &[u8]) -> bool
 struct PendingLoad {
     // The bytes loaded so far. Reset to an empty vector once loading
     // is complete and the buffer has been transmitted to the decoder.
-    bytes: Vec<u8>,
+    bytes: ImageBytes,
 
     // Image metadata, if available.
     metadata: Option<ImageMetadata>,
@@ -71,6 +71,40 @@ struct PendingLoad {
     url: ServoUrl,
 }
 
+enum ImageBytes {
+    InProgress(Vec<u8>),
+    Complete(Arc<Vec<u8>>),
+}
+
+impl ImageBytes {
+    fn extend_from_slice(&mut self, data: &[u8]) {
+        match *self {
+            ImageBytes::InProgress(ref mut bytes) => bytes.extend_from_slice(data),
+            ImageBytes::Complete(_) => panic!("attempted modification of complete image bytes"),
+        }
+    }
+
+    fn mark_complete(&mut self) -> Arc<Vec<u8>> {
+        let bytes = {
+            let own_bytes = match *self {
+                ImageBytes::InProgress(ref mut bytes) => bytes,
+                ImageBytes::Complete(_) => panic!("attempted modification of complete image bytes"),
+            };
+            mem::replace(own_bytes, vec![])
+        };
+        let bytes = Arc::new(bytes);
+        *self = ImageBytes::Complete(bytes.clone());
+        bytes
+    }
+
+    fn as_slice(&self) -> &[u8] {
+        match *self {
+            ImageBytes::InProgress(ref bytes) => &bytes,
+            ImageBytes::Complete(ref bytes) => &*bytes,
+        }
+    }
+}
+
 enum LoadResult {
     Loaded(Image),
     PlaceholderLoaded(Arc<Image>),
@@ -80,7 +114,7 @@ enum LoadResult {
 impl PendingLoad {
     fn new(url: ServoUrl) -> PendingLoad {
         PendingLoad {
-            bytes: vec!(),
+            bytes: ImageBytes::InProgress(vec!()),
             metadata: None,
             result: None,
             listeners: vec!(),
@@ -216,8 +250,6 @@ struct ResourceLoadInfo {
 
 /// Implementation of the image cache
 struct ImageCache {
-    progress_sender: Sender<ResourceLoadInfo>,
-
     decoder_sender: Sender<DecoderMsg>,
 
     // Worker threads for decoding images.
@@ -245,7 +277,6 @@ struct DecoderMsg {
 struct Receivers {
     cmd_receiver: Receiver<ImageCacheCommand>,
     decoder_receiver: Receiver<DecoderMsg>,
-    progress_receiver: Receiver<ResourceLoadInfo>,
 }
 
 impl Receivers {
@@ -253,16 +284,12 @@ impl Receivers {
     fn recv(&self) -> SelectResult {
         let cmd_receiver = &self.cmd_receiver;
         let decoder_receiver = &self.decoder_receiver;
-        let progress_receiver = &self.progress_receiver;
         select! {
             msg = cmd_receiver.recv() => {
                 SelectResult::Command(msg.unwrap())
             },
             msg = decoder_receiver.recv() => {
                 SelectResult::Decoder(msg.unwrap())
-            },
-            msg = progress_receiver.recv() => {
-                SelectResult::Progress(msg.unwrap())
             }
         }
     }
@@ -271,7 +298,6 @@ impl Receivers {
 /// The types of messages that the main image cache thread receives.
 enum SelectResult {
     Command(ImageCacheCommand),
-    Progress(ResourceLoadInfo),
     Decoder(DecoderMsg),
 }
 
@@ -316,10 +342,8 @@ impl ImageCache {
         // Ask the router to proxy messages received over IPC to us.
         let cmd_receiver = ROUTER.route_ipc_receiver_to_new_mpsc_receiver(ipc_command_receiver);
 
-        let (progress_sender, progress_receiver) = channel();
         let (decoder_sender, decoder_receiver) = channel();
         let mut cache = ImageCache {
-            progress_sender: progress_sender,
             decoder_sender: decoder_sender,
             thread_pool: ThreadPool::new(4),
             pending_loads: AllPendingLoads::new(),
@@ -331,7 +355,6 @@ impl ImageCache {
         let receivers = Receivers {
             cmd_receiver: cmd_receiver,
             decoder_receiver: decoder_receiver,
-            progress_receiver: progress_receiver,
         };
 
         let mut exit_sender: Option<IpcSender<()>> = None;
@@ -341,9 +364,6 @@ impl ImageCache {
                 SelectResult::Command(cmd) => {
                     exit_sender = cache.handle_cmd(cmd);
                 }
-                SelectResult::Progress(msg) => {
-                    cache.handle_progress(msg);
-                }
                 SelectResult::Decoder(msg) => {
                     cache.handle_decoder(msg);
                 }
@@ -395,14 +415,14 @@ impl ImageCache {
                 pending_load.bytes.extend_from_slice(&data);
                 //jmr0 TODO: possibly move to another task?
                 if let None = pending_load.metadata {
-                    if let Ok(metadata) = load_from_buf(&pending_load.bytes) {
+                    if let Ok(metadata) = load_from_buf(&pending_load.bytes.as_slice()) {
                         let dimensions = metadata.dimensions();
                         let img_metadata = ImageMetadata { width: dimensions.width,
-                                                         height: dimensions.height };
-                        pending_load.metadata = Some(img_metadata.clone());
+                                                           height: dimensions.height };
                         for listener in &pending_load.listeners {
                             listener.respond(ImageResponse::MetadataLoaded(img_metadata.clone()));
                         }
+                        pending_load.metadata = Some(img_metadata);
                     }
                 }
             }
@@ -411,15 +431,11 @@ impl ImageCache {
                     Ok(()) => {
                         let pending_load = self.pending_loads.get_by_key_mut(&msg.key).unwrap();
                         pending_load.result = Some(result);
-                        let bytes = mem::replace(&mut pending_load.bytes, vec!());
+                        let bytes = pending_load.bytes.mark_complete();
                         let sender = self.decoder_sender.clone();
 
                         self.thread_pool.execute(move || {
-                            let image = load_from_memory(&bytes);
-                            let msg = DecoderMsg {
-                                key: key,
-                                image: image
-                            };
+                            let msg = decode_bytes_sync(key, &*bytes);
                             sender.send(msg).unwrap();
                         });
                     }
@@ -448,7 +464,10 @@ impl ImageCache {
 
     // Change state of a url from pending -> loaded.
     fn complete_load(&mut self, key: LoadKey, mut load_result: LoadResult) {
-        let pending_load = self.pending_loads.remove(&key).unwrap();
+        let pending_load = match self.pending_loads.remove(&key) {
+            Some(load) => load,
+            None => return,
+        };
 
         match load_result {
             LoadResult::Loaded(ref mut image) => {
@@ -502,39 +521,64 @@ impl ImageCache {
     }
 
     /// Return a completed image if it exists, or None if there is no complete load
-    /// of the complete load is not fully decoded or is unavailable.
+    /// or the complete load is not fully decoded or is unavailable.
+    fn get_completed_image_if_available(&self,
+                                        url: &ServoUrl,
+                                        placeholder: UsePlaceholder)
+                                        -> Option<Result<ImageOrMetadataAvailable, ImageState>> {
+        self.completed_loads.get(url).map(|completed_load| {
+            match (&completed_load.image_response, placeholder) {
+                (&ImageResponse::Loaded(ref image), _) |
+                (&ImageResponse::PlaceholderLoaded(ref image), UsePlaceholder::Yes) => {
+                    Ok(ImageOrMetadataAvailable::ImageAvailable(image.clone()))
+                }
+                (&ImageResponse::PlaceholderLoaded(_), UsePlaceholder::No) |
+                (&ImageResponse::None, _) |
+                (&ImageResponse::MetadataLoaded(_), _) => {
+                    Err(ImageState::LoadError)
+                }
+            }
+        })
+    }
+
+    /// Return any available metadata or image for the given URL, or an indication that
+    /// the image is not yet available if it is in progress, or else reserve a slot in
+    /// the cache for the URL if the consumer can request images.
     fn get_image_or_meta_if_available(&mut self,
                                       url: ServoUrl,
                                       placeholder: UsePlaceholder,
                                       can_request: CanRequestImages)
                                       -> Result<ImageOrMetadataAvailable, ImageState> {
-        match self.completed_loads.get(&url) {
-            Some(completed_load) => {
-                match (completed_load.image_response.clone(), placeholder) {
-                    (ImageResponse::Loaded(image), _) |
-                    (ImageResponse::PlaceholderLoaded(image), UsePlaceholder::Yes) => {
-                        Ok(ImageOrMetadataAvailable::ImageAvailable(image))
-                    }
-                    (ImageResponse::PlaceholderLoaded(_), UsePlaceholder::No) |
-                    (ImageResponse::None, _) |
-                    (ImageResponse::MetadataLoaded(_), _) => {
-                        Err(ImageState::LoadError)
-                    }
-                }
-            }
-            None => {
-                let result = self.pending_loads.get_cached(url, can_request);
-                match result {
-                    CacheResult::Hit(key, pl) => match pl.metadata {
-                        Some(ref meta) =>
-                            Ok(ImageOrMetadataAvailable::MetadataAvailable(meta.clone())),
-                        None =>
-                            Err(ImageState::Pending(key)),
-                    },
-                    CacheResult::Miss(Some((key, _pl))) => Err(ImageState::NotRequested(key)),
-                    CacheResult::Miss(None) => Err(ImageState::LoadError),
-                }
+        if let Some(result) = self.get_completed_image_if_available(&url, placeholder) {
+            return result;
+        }
+
+        let decoded = {
+            let result = self.pending_loads.get_cached(url.clone(), can_request);
+            match result {
+                CacheResult::Hit(key, pl) => match (&pl.result, &pl.metadata) {
+                    (&Some(Ok(_)), _) =>
+                        decode_bytes_sync(key, &pl.bytes.as_slice()),
+                    (&None, &Some(ref meta)) =>
+                        return Ok(ImageOrMetadataAvailable::MetadataAvailable(meta.clone())),
+                    (&Some(Err(_)), _) | (&None, &None) =>
+                        return Err(ImageState::Pending(key)),
+                },
+                CacheResult::Miss(Some((key, _pl))) =>
+                    return Err(ImageState::NotRequested(key)),
+                CacheResult::Miss(None) =>
+                    return Err(ImageState::LoadError),
             }
+        };
+
+        // In the case where a decode is ongoing (or waiting in a queue) but we have the
+        // full response available, we decode the bytes synchronously and ignore the
+        // async decode when it finishes later.
+        // TODO: make this behaviour configurable according to the caller's needs.
+        self.handle_decoder(decoded);
+        match self.get_completed_image_if_available(&url, placeholder) {
+            Some(result) => result,
+            None => Err(ImageState::LoadError),
         }
     }
 
@@ -542,12 +586,12 @@ impl ImageCache {
                           id: PendingImageId,
                           loaded_bytes: Vec<u8>) {
         let action = FetchResponseMsg::ProcessResponseChunk(loaded_bytes);
-        let _ = self.progress_sender.send(ResourceLoadInfo {
+        self.handle_progress(ResourceLoadInfo {
             action: action,
             key: id,
         });
         let action = FetchResponseMsg::ProcessResponseEOF(Ok(()));
-        let _ = self.progress_sender.send(ResourceLoadInfo {
+        self.handle_progress(ResourceLoadInfo {
             action: action,
             key: id,
         });
@@ -564,3 +608,11 @@ pub fn new_image_cache_thread(webrender_api: webrender_traits::RenderApi) -> Ima
 
     ImageCacheThread::new(ipc_command_sender)
 }
+
+fn decode_bytes_sync(key: LoadKey, bytes: &[u8]) -> DecoderMsg {
+    let image = load_from_memory(bytes);
+    DecoderMsg {
+        key: key,
+        image: image
+    }
+}