Remove wait-time when opening settings panel (#8464)

### Related
* Closes #8263

### What
I couldn't stand the half-second delay when opening the options screen.
Rerun needs to feel snappy!

Gettings the ffmpeg version is now done on a background thread, showing
s spinner until it is done.

Unfortunately we still have to wait for ffmpeg when starting up an H.264
video on native. We could fix that by pre-warming the cache though 🤔

---------

Co-authored-by: Clement Rey <[email protected]>
Co-authored-by: Andreas Reich <[email protected]>

Author: 3 people

Cargo.lock

@@ -6511,6 +6511,7 @@ dependencies = [
  "js-sys",
  "once_cell",
  "parking_lot",
+ "poll-promise",
  "re_build_info",
  "re_build_tools",
  "re_log",

crates/utils/re_video/Cargo.toml

@@ -53,6 +53,7 @@ econtext.workspace = true
 itertools.workspace = true
 once_cell.workspace = true
 parking_lot.workspace = true
+poll-promise.workspace = true
 re_mp4.workspace = true
 thiserror.workspace = true
 

crates/utils/re_video/src/decode/ffmpeg_h264/ffmpeg.rs

@@ -811,7 +811,7 @@ impl FFmpegCliH264Decoder {
 
         // Check the version once ahead of running FFmpeg.
         // The error is still handled if it happens while running FFmpeg, but it's a bit unclear if we can get it to start in the first place then.
-        match FFmpegVersion::for_executable(ffmpeg_path.as_deref()) {
+        match FFmpegVersion::for_executable_blocking(ffmpeg_path.as_deref()) {
             Ok(version) => {
                 if !version.is_compatible() {
                     return Err(Error::UnsupportedFFmpegVersion {

crates/utils/re_video/src/decode/ffmpeg_h264/version.rs

@@ -1,14 +1,17 @@
-use std::{collections::HashMap, path::PathBuf};
+use std::{collections::HashMap, path::PathBuf, task::Poll};
 
 use once_cell::sync::Lazy;
 use parking_lot::Mutex;
+use poll_promise::Promise;
 
 // FFmpeg 5.1 "Riemann" is from 2022-07-22.
 // It's simply the oldest I tested manually as of writing. We might be able to go lower.
 // However, we also know that FFmpeg 4.4 is already no longer working.
 pub const FFMPEG_MINIMUM_VERSION_MAJOR: u32 = 5;
 pub const FFMPEG_MINIMUM_VERSION_MINOR: u32 = 1;
 
+pub type FfmpegVersionResult = Result<FFmpegVersion, FFmpegVersionParseError>;
+
 /// A successfully parsed `FFmpeg` version.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct FFmpegVersion {
@@ -78,61 +81,31 @@ impl FFmpegVersion {
     /// version string. Since version strings can get pretty wild, we don't want to fail in this case.
     ///
     /// Internally caches the result per path together with its modification time to re-run/parse the version only if the file has changed.
-    pub fn for_executable(path: Option<&std::path::Path>) -> Result<Self, FFmpegVersionParseError> {
-        type VersionMap = HashMap<
-            PathBuf,
-            (
-                Option<std::time::SystemTime>,
-                Result<FFmpegVersion, FFmpegVersionParseError>,
-            ),
-        >;
-        static CACHE: Lazy<Mutex<VersionMap>> = Lazy::new(|| Mutex::new(HashMap::new()));
-
+    pub fn for_executable_poll(path: Option<&std::path::Path>) -> Poll<FfmpegVersionResult> {
         re_tracing::profile_function!();
 
-        // Retrieve file modification time first.
-        let modification_time = if let Some(path) = path {
-            path.metadata()
-                .map_err(|err| {
-                    FFmpegVersionParseError::RetrieveFileModificationTime(err.to_string())
-                })?
-                .modified()
-                .ok()
-        } else {
-            None
-        };
-
-        // Check first if we already have the version cached.
-        let mut cache = CACHE.lock();
-        let cache_key = path.unwrap_or(std::path::Path::new("ffmpeg"));
-        if let Some(cached) = cache.get(cache_key) {
-            if modification_time == cached.0 {
-                return cached.1.clone();
-            }
-        }
-
-        // Run FFmpeg (or whatever was passed to us) to get the version.
-        let raw_version = if let Some(path) = path {
-            ffmpeg_sidecar::version::ffmpeg_version_with_path(path)
-        } else {
-            ffmpeg_sidecar::version::ffmpeg_version()
-        }
-        .map_err(|err| FFmpegVersionParseError::RunFFmpeg(err.to_string()))?;
-
-        let version = if let Some(version) = Self::parse(&raw_version) {
-            Ok(version)
-        } else {
-            Err(FFmpegVersionParseError::ParseVersion {
-                raw_version: raw_version.clone(),
-            })
-        };
+        let modification_time = file_modification_time(path)?;
+        VersionCache::global(|cache| {
+            cache
+                .version(path, modification_time)
+                .poll()
+                .map(|r| r.clone())
+        })
+    }
 
-        cache.insert(
-            cache_key.to_path_buf(),
-            (modification_time, version.clone()),
-        );
+    /// Like [`Self::for_executable_poll`], but blocks until the version is ready.
+    ///
+    /// WARNING: this blocks for half a second on Mac the first time this is called with a given path, maybe more on other platforms.
+    pub fn for_executable_blocking(path: Option<&std::path::Path>) -> FfmpegVersionResult {
+        re_tracing::profile_function!();
 
-        version
+        let modification_time = file_modification_time(path)?;
+        VersionCache::global(|cache| {
+            cache
+                .version(path, modification_time)
+                .block_until_ready()
+                .clone()
+        })
     }
 
     /// Returns true if this version is compatible with Rerun's minimum requirements.
@@ -143,6 +116,72 @@ impl FFmpegVersion {
     }
 }
 
+fn file_modification_time(
+    path: Option<&std::path::Path>,
+) -> Result<Option<std::time::SystemTime>, FFmpegVersionParseError> {
+    Ok(if let Some(path) = path {
+        path.metadata()
+            .map_err(|err| FFmpegVersionParseError::RetrieveFileModificationTime(err.to_string()))?
+            .modified()
+            .ok()
+    } else {
+        None
+    })
+}
+
+#[derive(Default)]
+struct VersionCache(
+    HashMap<PathBuf, (Option<std::time::SystemTime>, Promise<FfmpegVersionResult>)>,
+);
+
+impl VersionCache {
+    fn global<R>(f: impl FnOnce(&mut Self) -> R) -> R {
+        static CACHE: Lazy<Mutex<VersionCache>> = Lazy::new(|| Mutex::new(VersionCache::default()));
+        f(&mut CACHE.lock())
+    }
+
+    fn version(
+        &mut self,
+        path: Option<&std::path::Path>,
+        modification_time: Option<std::time::SystemTime>,
+    ) -> &Promise<FfmpegVersionResult> {
+        let Self(cache) = self;
+
+        let cache_key = path.unwrap_or(std::path::Path::new("ffmpeg")).to_path_buf();
+
+        match cache.entry(cache_key) {
+            std::collections::hash_map::Entry::Occupied(entry) => &entry.into_mut().1,
+            std::collections::hash_map::Entry::Vacant(entry) => {
+                let path = path.map(|path| path.to_path_buf());
+                let version =
+                    Promise::spawn_thread("ffmpeg_version", move || ffmpeg_version(path.as_ref()));
+                &entry.insert((modification_time, version)).1
+            }
+        }
+    }
+}
+
+fn ffmpeg_version(
+    path: Option<&std::path::PathBuf>,
+) -> Result<FFmpegVersion, FFmpegVersionParseError> {
+    re_tracing::profile_function!("ffmpeg_version_with_path");
+
+    let raw_version = if let Some(path) = path {
+        ffmpeg_sidecar::version::ffmpeg_version_with_path(path)
+    } else {
+        ffmpeg_sidecar::version::ffmpeg_version()
+    }
+    .map_err(|err| FFmpegVersionParseError::RunFFmpeg(err.to_string()))?;
+
+    if let Some(version) = FFmpegVersion::parse(&raw_version) {
+        Ok(version)
+    } else {
+        Err(FFmpegVersionParseError::ParseVersion {
+            raw_version: raw_version.clone(),
+        })
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::decode::ffmpeg_h264::FFmpegVersion;

crates/viewer/re_viewer/src/ui/settings_screen.rs

@@ -203,6 +203,7 @@ fn video_section_ui(ui: &mut Ui, app_options: &mut AppOptions) {
 #[cfg(not(target_arch = "wasm32"))]
 fn ffmpeg_path_status_ui(ui: &mut Ui, app_options: &AppOptions) {
     use re_video::decode::{FFmpegVersion, FFmpegVersionParseError};
+    use std::task::Poll;
 
     let path = app_options
         .video_decoder_override_ffmpeg_path
@@ -211,25 +212,29 @@ fn ffmpeg_path_status_ui(ui: &mut Ui, app_options: &AppOptions) {
     if path.is_some_and(|path| !path.is_file()) {
         ui.error_label("The specified FFmpeg binary path does not exist or is not a file.");
     } else {
-        let res = FFmpegVersion::for_executable(path);
+        let res = FFmpegVersion::for_executable_poll(path);
 
         match res {
-            Ok(version) => {
+            Poll::Pending => {
+                ui.spinner();
+            }
+
+            Poll::Ready(Ok(version)) => {
                 if version.is_compatible() {
                     ui.success_label(format!("FFmpeg found (version {version})"));
                 } else {
                     ui.error_label(format!("Incompatible FFmpeg version: {version}"));
                 }
             }
-            Err(FFmpegVersionParseError::ParseVersion { raw_version }) => {
+            Poll::Ready(Err(FFmpegVersionParseError::ParseVersion { raw_version })) => {
                 // We make this one a warning instead of an error because version parsing is flaky, and
                 // it might end up still working.
                 ui.warning_label(format!(
                     "FFmpeg binary found but unable to parse version: {raw_version}"
                 ));
             }
 
-            Err(err) => {
+            Poll::Ready(Err(err)) => {
                 ui.error_label(format!("Unable to check FFmpeg version: {err}"));
             }
         }