Auto merge of #22938 - asajeffrey:webvr-future-frame-data, r=paulrouget

Use webvr future_frame_data to avoid blocking the WebGL thread

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This PR fixes a potential deadlock caused by the WebGL thread being blocked on a VR device. Rather than blocking on the VR device, it forwards a future to the script thread, and then then script thread blocks.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's fixing a potential deadlock

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6 files changed, 17 insertions, 13 deletions

diff --git a/components/canvas_traits/Cargo.toml b/components/canvas_traits/Cargo.toml
index 9d022072511..298e1d4740a 100644
--- a/components/canvas_traits/Cargo.toml
+++ b/components/canvas_traits/Cargo.toml
@@ -27,3 +27,4 @@ serde = "1.0"
 serde_bytes = "0.10"
 servo_config = {path = "../config"}
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
+webvr_traits = {path = "../webvr_traits"}
diff --git a/components/canvas_traits/webgl.rs b/components/canvas_traits/webgl.rs
index 6b34965ae61..cfa885daa0b 100644
--- a/components/canvas_traits/webgl.rs
+++ b/components/canvas_traits/webgl.rs
@@ -7,12 +7,12 @@ use gleam::gl;
 use ipc_channel::ipc::{IpcBytesReceiver, IpcBytesSender, IpcSharedMemory};
 use offscreen_gl_context::{GLContextAttributes, GLLimits};
 use pixels::PixelFormat;
-use serde_bytes::ByteBuf;
 use std::borrow::Cow;
 use std::fmt;
 use std::num::NonZeroU32;
 use std::ops::Deref;
 use webrender_api::{DocumentId, ImageKey, PipelineId};
+use webvr_traits::WebVRFutureFrameData;
 
 /// Helper function that creates a WebGL channel (WebGLSender, WebGLReceiver) to be used in WebGLCommands.
 pub use crate::webgl_channel::webgl_channel;
@@ -506,7 +506,12 @@ pub enum WebVRCommand {
     /// Start presenting to a VR device.
     Create(WebVRDeviceId),
     /// Synchronize the pose information to be used in the frame.
-    SyncPoses(WebVRDeviceId, f64, f64, WebGLSender<Result<ByteBuf, ()>>),
+    SyncPoses(
+        WebVRDeviceId,
+        f64,
+        f64,
+        WebGLSender<Result<WebVRFutureFrameData, ()>>,
+    ),
     /// Submit the frame to a VR device using the specified texture coordinates.
     SubmitFrame(WebVRDeviceId, [f32; 4], [f32; 4]),
     /// Stop presenting to a VR device
diff --git a/components/script/dom/vrdisplay.rs b/components/script/dom/vrdisplay.rs
index dd8f29195b7..e806afb7a22 100644
--- a/components/script/dom/vrdisplay.rs
+++ b/components/script/dom/vrdisplay.rs
@@ -42,13 +42,13 @@ use crossbeam_channel::{unbounded, Sender};
 use dom_struct::dom_struct;
 use ipc_channel::ipc::IpcSender;
 use profile_traits::ipc;
-use serde_bytes::ByteBuf;
 use std::cell::Cell;
 use std::mem;
 use std::ops::Deref;
 use std::rc::Rc;
 use std::thread;
-use webvr_traits::{WebVRDisplayData, WebVRDisplayEvent, WebVRFrameData, WebVRLayer, WebVRMsg};
+use webvr_traits::{WebVRDisplayData, WebVRDisplayEvent, WebVRFrameData, WebVRFutureFrameData};
+use webvr_traits::{WebVRLayer, WebVRMsg};
 
 #[dom_struct]
 pub struct VRDisplay {
@@ -77,7 +77,7 @@ pub struct VRDisplay {
     // Compositor VRFrameData synchonization
     frame_data_status: Cell<VRFrameDataStatus>,
     #[ignore_malloc_size_of = "closures are hard"]
-    frame_data_receiver: DomRefCell<Option<WebGLReceiver<Result<ByteBuf, ()>>>>,
+    frame_data_receiver: DomRefCell<Option<WebGLReceiver<Result<WebVRFutureFrameData, ()>>>>,
     running_display_raf: Cell<bool>,
     paused: Cell<bool>,
     stopped_on_pause: Cell<bool>,
@@ -664,8 +664,8 @@ impl VRDisplay {
     fn sync_frame_data(&self) {
         let status = if let Some(receiver) = self.frame_data_receiver.borrow().as_ref() {
             match receiver.recv().unwrap() {
-                Ok(bytes) => {
-                    *self.frame_data.borrow_mut() = WebVRFrameData::from_bytes(&bytes[..]);
+                Ok(future_data) => {
+                    *self.frame_data.borrow_mut() = future_data.block();
                     VRFrameDataStatus::Synced
                 },
                 Err(()) => VRFrameDataStatus::Exit,
diff --git a/components/webvr/webvr_thread.rs b/components/webvr/webvr_thread.rs
index 2d55fa8deac..4ce25bccb50 100644
--- a/components/webvr/webvr_thread.rs
+++ b/components/webvr/webvr_thread.rs
@@ -385,11 +385,8 @@ impl webgl::WebVRRenderHandler for WebVRCompositorHandler {
             },
             webgl::WebVRCommand::SyncPoses(compositor_id, near, far, sender) => {
                 if let Some(compositor) = self.compositors.get(&compositor_id) {
-                    let pose = unsafe {
-                        (*compositor.0).sync_poses();
-                        (*compositor.0).synced_frame_data(near, far).to_bytes()
-                    };
-                    let _ = sender.send(Ok(pose.into()));
+                    let pose = unsafe { (*compositor.0).future_frame_data(near, far) };
+                    let _ = sender.send(Ok(pose));
                 } else {
                     let _ = sender.send(Err(()));
                 }
diff --git a/components/webvr_traits/Cargo.toml b/components/webvr_traits/Cargo.toml
index 7228e4e621d..6caceda3ac4 100644
--- a/components/webvr_traits/Cargo.toml
+++ b/components/webvr_traits/Cargo.toml
@@ -13,5 +13,5 @@ path = "lib.rs"
 [dependencies]
 ipc-channel = "0.11"
 msg = {path = "../msg"}
-rust-webvr-api = {version = "0.10", features = ["serde-serialization"]}
+rust-webvr-api = {version = "0.10.2", features = ["ipc"]}
 serde = "1.0"
diff --git a/components/webvr_traits/lib.rs b/components/webvr_traits/lib.rs
index 9ebae6e65dc..04dfca47fad 100644
--- a/components/webvr_traits/lib.rs
+++ b/components/webvr_traits/lib.rs
@@ -20,6 +20,7 @@ pub use rust_webvr_api::VREye as WebVREye;
 pub use rust_webvr_api::VREyeParameters as WebVREyeParameters;
 pub use rust_webvr_api::VRFieldOfView as WebVRFieldOfView;
 pub use rust_webvr_api::VRFrameData as WebVRFrameData;
+pub use rust_webvr_api::VRFutureFrameData as WebVRFutureFrameData;
 pub use rust_webvr_api::VRGamepadButton as WebVRGamepadButton;
 pub use rust_webvr_api::VRGamepadData as WebVRGamepadData;
 pub use rust_webvr_api::VRGamepadEvent as WebVRGamepadEvent;