egl: Add wrapper for EGLSync

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Unreleased
 
+- Add `api::egl::sync::Sync` to wrap `EGLSync`
+- Add ability to import and export an a sync fd from a `api::egl::sync::Sync`
+
 # Version 0.31.1
 
 - Fixed `CGLContextObj` having an invalid encoding on newer macOS versions.

glutin/src/api/egl/display.rs

@@ -231,6 +231,91 @@ impl Display {
         }
     }
 
+    /// Create a sync.
+    ///
+    /// Creating a sync fence requires that an EGL context is currently bound.
+    /// Otherwise [`ErrorKind::BadMatch`] is returned.
+    ///
+    /// This function returns [`Err`] if the EGL version is not at least 1.5
+    /// or `EGL_KHR_fence_sync` is not available. An error is also returned if
+    /// native fences are not supported.
+    pub fn create_sync(&self, native: bool) -> Result<super::sync::Sync> {
+        if self.inner.version < super::VERSION_1_5
+            && !self.inner.display_extensions.contains("EGL_KHR_fence_sync")
+        {
+            return Err(ErrorKind::NotSupported("Sync objects are not supported").into());
+        }
+
+        if native && !self.inner.display_extensions.contains("EGL_ANDROID_native_fence_sync") {
+            return Err(ErrorKind::NotSupported("Native fences are not supported").into());
+        }
+
+        let ty = if native { egl::SYNC_NATIVE_FENCE_ANDROID } else { egl::SYNC_FENCE_KHR };
+        let sync = unsafe { self.inner.egl.CreateSyncKHR(*self.inner.raw, ty, ptr::null()) };
+
+        if sync == egl::NO_SYNC {
+            return Err(super::check_error().err().unwrap());
+        }
+
+        Ok(super::sync::Sync(Arc::new(super::sync::Inner {
+            inner: sync,
+            display: self.inner.clone(),
+        })))
+    }
+
+    /// Import a sync fd into EGL.
+    ///
+    /// Glutin will duplicate the sync fd being imported since EGL assumes
+    /// ownership of the file descriptor. If the file descriptor could not
+    /// be cloned, then [`ErrorKind::BadParameter`] is returned.
+    ///
+    /// This function returns [`ErrorKind::NotSupported`] if the
+    /// `EGL_ANDROID_native_fence_sync` extension is not available.
+    #[cfg(unix)]
+    pub fn import_sync(
+        &self,
+        fd: std::os::unix::prelude::BorrowedFd<'_>,
+    ) -> Result<super::sync::Sync> {
+        use std::mem;
+        use std::os::unix::prelude::AsRawFd;
+
+        // The specification states that EGL_KHR_fence_sync must be available,
+        // and therefore does not need to be tested.
+        if !self.inner.display_extensions.contains("EGL_ANDROID_native_fence_sync") {
+            return Err(ErrorKind::NotSupported("Importing a sync fd is not supported").into());
+        }
+
+        let import = fd.try_clone_to_owned().map_err(|_| ErrorKind::BadParameter)?;
+
+        let attrs: [EGLint; 3] =
+            [egl::SYNC_NATIVE_FENCE_FD_ANDROID as EGLint, import.as_raw_fd(), egl::NONE as EGLint];
+
+        // SAFETY:
+        // - The EGL implementation advertised EGL_ANDROID_native_fence_sync
+        // - The fd being imported is an OwnedFd, meaning ownership is transfered to
+        //   EGL.
+        let sync = unsafe {
+            self.inner.egl.CreateSyncKHR(
+                *self.inner.raw,
+                egl::SYNC_NATIVE_FENCE_ANDROID,
+                attrs.as_ptr(),
+            )
+        };
+
+        if sync == egl::NO_SYNC {
+            // Drop will implicitly close the duplicated file descriptor.
+            return Err(super::check_error().err().unwrap());
+        }
+
+        // Successful import means EGL assumes ownership of the file descriptor.
+        mem::forget(import);
+
+        Ok(super::sync::Sync(Arc::new(super::sync::Inner {
+            inner: sync,
+            display: self.inner.clone(),
+        })))
+    }
+
     fn get_platform_display(egl: &Egl, display: RawDisplayHandle) -> Result<EglDisplay> {
         if !egl.GetPlatformDisplay.is_loaded() {
             return Err(ErrorKind::NotSupported("eglGetPlatformDisplay is not supported").into());

glutin/src/api/egl/mod.rs

@@ -19,6 +19,7 @@ use libloading::os::unix as libloading_os;
 #[cfg(windows)]
 use libloading::os::windows as libloading_os;
 
+use crate::context::Version;
 use crate::error::{Error, ErrorKind, Result};
 use crate::lib_loading::{SymLoading, SymWrapper};
 
@@ -27,6 +28,7 @@ pub mod context;
 pub mod device;
 pub mod display;
 pub mod surface;
+pub mod sync;
 
 pub(crate) static EGL: Lazy<Option<Egl>> = Lazy::new(|| {
     #[cfg(windows)]
@@ -41,6 +43,8 @@ pub(crate) static EGL: Lazy<Option<Egl>> = Lazy::new(|| {
 type EglGetProcAddress = unsafe extern "C" fn(*const ffi::c_void) -> *const ffi::c_void;
 static EGL_GET_PROC_ADDRESS: OnceCell<libloading_os::Symbol<EglGetProcAddress>> = OnceCell::new();
 
+const VERSION_1_5: Version = Version { major: 1, minor: 5 };
+
 pub(crate) struct Egl(pub SymWrapper<egl::Egl>);
 
 unsafe impl Sync for Egl {}

glutin/src/api/egl/sync.rs

@@ -0,0 +1,166 @@
+//! EGL Sync Fences.
+
+use std::ffi::c_void;
+use std::mem::MaybeUninit;
+use std::sync::Arc;
+use std::time::Duration;
+
+use glutin_egl_sys::egl::types::{EGLenum, EGLint};
+
+use super::display::DisplayInner;
+use super::{egl, ErrorKind, VERSION_1_5};
+use crate::error::Result;
+
+/// EGL sync object.
+#[derive(Debug, Clone)]
+pub struct Sync(pub(super) Arc<Inner>);
+
+impl Sync {
+    /// Insert this sync into the currently bound context.
+    ///
+    /// If the EGL version is not at least 1.5 or the `EGL_KHR_wait_sync`
+    /// extension is not available, this returns [`ErrorKind::NotSupported`].
+    ///
+    /// This will return [`ErrorKind::BadParameter`] if there is no currently
+    /// bound context.
+    pub fn wait(&self) -> Result<()> {
+        if self.0.display.version < VERSION_1_5
+            && !self.0.display.display_extensions.contains("EGL_KHR_wait_sync")
+        {
+            return Err(ErrorKind::NotSupported(
+                "Sync::wait is not supported if EGL_KHR_wait_sync isn't available",
+            )
+            .into());
+        }
+
+        if unsafe { self.0.display.egl.WaitSyncKHR(*self.0.display.raw, self.0.inner, 0) }
+            == egl::FALSE as EGLint
+        {
+            return Err(super::check_error().err().unwrap());
+        }
+
+        Ok(())
+    }
+
+    /// Query if the sync is already
+    pub fn is_signalled(&self) -> Result<bool> {
+        let status = unsafe { self.get_attrib(egl::SYNC_STATUS) }? as EGLenum;
+        Ok(status == egl::SIGNALED)
+    }
+
+    /// Block and wait for the sync object to be signalled.
+    ///
+    /// A timeout of [`None`] will wait forever. If the timeout is [`Some`], the
+    /// maximum timeout is [`u64::MAX`] - 1 nanoseconds. Anything larger will be
+    /// truncated. If the timeout is reached this function returns [`false`].
+    ///
+    /// If `flush` is [`true`], the currently bound context is flushed.
+    pub fn client_wait(&self, timeout: Option<Duration>, flush: bool) -> Result<bool> {
+        let flags = if flush { egl::SYNC_FLUSH_COMMANDS_BIT } else { 0 };
+        let timeout = timeout
+            .as_ref()
+            .map(Duration::as_nanos)
+            .map(|nanos| nanos.max(u128::from(u64::MAX)) as u64)
+            .unwrap_or(egl::FOREVER);
+
+        let result = unsafe {
+            self.0.display.egl.ClientWaitSyncKHR(
+                *self.0.display.raw,
+                self.0.inner,
+                flags as EGLint,
+                timeout,
+            )
+        } as EGLenum;
+
+        match result {
+            egl::FALSE => Err(super::check_error().err().unwrap()),
+            egl::TIMEOUT_EXPIRED => Ok(false),
+            egl::CONDITION_SATISFIED => Ok(true),
+            _ => unreachable!(),
+        }
+    }
+
+    /// Export the fence's underlying sync fd.
+    ///
+    /// Returns [`ErrorKind::NotSupported`] if the sync is not a native fence.
+    ///
+    /// # Availability
+    ///
+    /// This is available on Android and Linux when the
+    /// `EGL_ANDROID_native_fence_sync` extension is available.
+    #[cfg(unix)]
+    pub fn export_sync_fd(&self) -> Result<std::os::unix::prelude::OwnedFd> {
+        // Invariants:
+        // - EGL_KHR_fence_sync must be supported if a Sync is creatable.
+        use std::os::unix::prelude::FromRawFd;
+
+        // Check the type of the fence to see if it can be exported.
+        let ty = unsafe { self.get_attrib(egl::SYNC_TYPE) }?;
+
+        // SAFETY: GetSyncAttribKHR was successful.
+        if ty as EGLenum != egl::SYNC_NATIVE_FENCE_ANDROID {
+            return Err(ErrorKind::NotSupported("The sync is not a native fence").into());
+        }
+
+        // SAFETY: The fence type is SYNC_NATIVE_FENCE_ANDROID, making it possible to
+        // export the native fence.
+        let fd = unsafe {
+            self.0.display.egl.DupNativeFenceFDANDROID(*self.0.display.raw, self.0.inner)
+        };
+
+        if fd == egl::NO_NATIVE_FENCE_FD_ANDROID {
+            return Err(super::check_error().err().unwrap());
+        }
+
+        // SAFETY:
+        // - The file descriptor from EGL is valid if the return value is not
+        //   NO_NATIVE_FENCE_FD_ANDROID.
+        // - The EGL implemention duplicates the underlying file descriptor and
+        //   transfers ownership to the application.
+        Ok(unsafe { std::os::unix::prelude::OwnedFd::from_raw_fd(fd) })
+    }
+
+    /// Get a raw handle to the `EGLSync`.
+    pub fn raw_device(&self) -> *const c_void {
+        self.0.inner
+    }
+
+    unsafe fn get_attrib(&self, attrib: EGLenum) -> Result<EGLint> {
+        let mut result = MaybeUninit::<EGLint>::uninit();
+
+        if unsafe {
+            self.0.display.egl.GetSyncAttribKHR(
+                *self.0.display.raw,
+                self.0.inner,
+                attrib as EGLint,
+                result.as_mut_ptr().cast(),
+            )
+        } == egl::FALSE
+        {
+            return Err(super::check_error().err().unwrap());
+        };
+
+        Ok(unsafe { result.assume_init() })
+    }
+}
+
+#[derive(Debug)]
+pub(super) struct Inner {
+    pub(super) inner: egl::types::EGLSyncKHR,
+    pub(super) display: Arc<DisplayInner>,
+}
+
+impl Drop for Inner {
+    fn drop(&mut self) {
+        // SAFETY: The Sync owns the underlying EGLSyncKHR
+        if unsafe { self.display.egl.DestroySyncKHR(*self.display.raw, self.inner) } == egl::FALSE {
+            // If this fails we can't do much in Drop. At least drain the error.
+            let _ = super::check_error();
+        }
+    }
+}
+
+// SAFETY: The Inner owns the sync and the display is valid.
+unsafe impl Send for Inner {}
+// SAFETY: EGL allows destroying the sync on any thread.
+unsafe impl std::marker::Sync for Inner {}

glutin_examples/examples/egl_sync.rs

@@ -0,0 +1,87 @@
+fn main() {
+    #[cfg(all(egl_backend))]
+    example::run();
+}
+
+#[cfg(all(egl_backend))]
+mod example {
+    use glutin::api::egl::display::Display;
+    use glutin::config::ConfigTemplate;
+    use glutin::context::{ContextApi, ContextAttributesBuilder};
+    use glutin::display::{GetDisplayExtensions, GlDisplay};
+    use glutin::prelude::GlConfig;
+    use raw_window_handle::HasRawDisplayHandle;
+    use winit::event_loop::EventLoop;
+
+    pub fn run() {
+        // We won't be displaying anything, but we will use winit to get
+        // access to some sort of platform display.
+        let event_loop = EventLoop::new().unwrap();
+
+        // Create the display for the platform.
+        let display = unsafe { Display::new(event_loop.raw_display_handle()) }.unwrap();
+
+        if !display.extensions().contains("EGL_KHR_fence_sync") {
+            eprintln!("EGL implementation does not support fence sync objects");
+            return;
+        }
+
+        // Now we need a context to draw to create a sync object.
+        let template = ConfigTemplate::default();
+        let config = unsafe { display.find_configs(template) }
+            .unwrap()
+            .reduce(
+                |config, acc| {
+                    if config.num_samples() > acc.num_samples() {
+                        config
+                    } else {
+                        acc
+                    }
+                },
+            )
+            .expect("No available configs");
+
+        println!("Picked a config with {} samples", config.num_samples());
+
+        let context_attributes =
+            ContextAttributesBuilder::new().with_context_api(ContextApi::Gles(None)).build(None);
+        let not_current = unsafe { display.create_context(&config, &context_attributes) }.unwrap();
+
+        // Make the context current, since we are not rendering we can do a surfaceless
+        // bind.
+        let _context = not_current.make_current_surfaceless().unwrap();
+
+        // Now a sync object can be created.
+        let sync = display.create_sync(false).unwrap();
+
+        // The sync object at this point is inserted into the command stream for the GL
+        // context.
+        //
+        // However we aren't recording any commands so the fence would already be
+        // signalled. Effecitvely it isn't useful to test the signalled value here.
+        sync.is_signalled().unwrap();
+
+        #[cfg(unix)]
+        {
+            if display.extensions().contains("EGL_ANDROID_native_fence_sync") {
+                use std::os::fd::AsFd;
+
+                println!("EGL Android native fence sync is supported");
+
+                // Glutin also supports exporting a sync fence.
+                // Firstly the sync must be a native fence.
+                let sync = display.create_sync(true).unwrap();
+
+                // An exported Sync FD can then be used in many ways, including:
+                // - Send the Sync FD to another processe to synchronize rendering
+                // - Import the Sync FD into another EGL Display
+                // - Import the Sync FD into Vulkan using VK_KHR_external_fence_fd.
+                let sync_fd = sync.export_sync_fd().expect("Export failed");
+
+                // To show that an exported sync fd can be imported, we will reimport the sync
+                // fd we just exported.
+                let _imported_sync = display.import_sync(sync_fd.as_fd()).expect("Import failed");
+            }
+        }
+    }
+}