Improve the docs of PipelineCache and friends (gfx-rs#6978)

jimblandy · Jan 23, 2025 · 5e2bcc9 · 5e2bcc9
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -83,6 +83,10 @@ By @brodycj in [#6925](https://github.com/gfx-rs/wgpu/pull/6925).
 
 - Stop naga causing undefined behavior when a ray query misses. By @Vecvec in [#6752](https://github.com/gfx-rs/wgpu/pull/6752).
 
+### Documentation
+
+- Improved documentation around pipeline caches. By @DJMcNab in [#6978](https://github.com/gfx-rs/wgpu/pull/6978).
+
 ## v24.0.0 (2025-01-15)
 
 ### Major changes

diff --git a/wgpu/src/api/common_pipeline.rs b/wgpu/src/api/common_pipeline.rs
@@ -40,7 +40,7 @@ impl Default for PipelineCompilationOptions<'_> {
 /// Describes a pipeline cache, which allows reusing compilation work
 /// between program runs.
 ///
-/// For use with [`Device::create_pipeline_cache`]
+/// For use with [`Device::create_pipeline_cache`].
 ///
 /// This type is unique to the Rust API of `wgpu`.
 #[derive(Clone, Debug)]

diff --git a/wgpu/src/api/pipeline_cache.rs b/wgpu/src/api/pipeline_cache.rs
@@ -5,7 +5,9 @@ use crate::*;
 /// in subsequent executions
 ///
 /// This reuse is only applicable for the same or similar devices.
-/// See [`util::pipeline_cache_key`] for some details.
+/// See [`util::pipeline_cache_key`] for some details and a suggested workflow.
+///
+/// Created using [`Device::create_pipeline_cache`].
 ///
 /// # Background
 ///
@@ -28,6 +30,7 @@ use crate::*;
 ///
 /// # Usage
 ///
+/// This is used as [`RenderPipelineDescriptor::cache`] or [`ComputePipelineDescriptor::cache`].
 /// It is valid to use this resource when creating multiple pipelines, in
 /// which case it will likely cache each of those pipelines.
 /// It is also valid to create a new cache for each pipeline.

diff --git a/wgpu/src/util/mod.rs b/wgpu/src/util/mod.rs
@@ -155,24 +155,43 @@ impl std::ops::Deref for DownloadBuffer {
 ///
 /// # Examples
 ///
-/// ``` no_run
+/// ```no_run
 /// # use std::path::PathBuf;
+/// use wgpu::PipelineCacheDescriptor;
 /// # let adapter_info = todo!();
-/// let cache_dir: PathBuf = PathBuf::new();
+/// # let device: wgpu::Device = todo!();
+/// let cache_dir: PathBuf = unimplemented!("Some reasonable platform-specific cache directory for your app.");
 /// let filename = wgpu::util::pipeline_cache_key(&adapter_info);
-/// if let Some(filename) = filename {
-///     let cache_file = cache_dir.join(&filename);
-///     let cache_data = std::fs::read(&cache_file);
-///     let pipeline_cache: wgpu::PipelineCache = todo!("Use data (if present) to create a pipeline cache");
+/// let (pipeline_cache, cache_file) = if let Some(filename) = filename {
+///     let cache_path = cache_dir.join(&filename);
+///     // If we failed to read the cache, for whatever reason, treat the data as lost.
+///     // In a real app, we'd probably avoid caching entirely unless the error was "file not found".
+///     let cache_data = std::fs::read(&cache_path).ok();
+///     let pipeline_cache = unsafe {
+///         device.create_pipeline_cache(&PipelineCacheDescriptor {
+///             data: cache_data.as_deref(),
+///             label: None,
+///             fallback: true
+///         })
+///     };
+///     (Some(pipeline_cache), Some(cache_path))
+/// } else {
+///     (None, None)
+/// };
 ///
+/// // Run pipeline initialisation, making sure to set the `cache`
+/// // fields of your `*PipelineDescriptor` to `pipeline_cache`
+///
+/// // And then save the resulting cache (probably off the main thread).
+/// if let (Some(pipeline_cache), Some(cache_file)) = (pipeline_cache, cache_file) {
 ///     let data = pipeline_cache.get_data();
 ///     if let Some(data) = data {
 ///         let temp_file = cache_file.with_extension("temp");
 ///         std::fs::write(&temp_file, &data)?;
 ///         std::fs::rename(&temp_file, &cache_file)?;
 ///     }
 /// }
-/// # Ok::<(), std::io::Error>(())
+/// # Ok::<_, std::io::Error>(())
 /// ```
 ///
 /// [`PipelineCache`]: super::PipelineCache