X11: Improve performance of Window::set_cursor_icon (#1116)

* X11: Fix performance issue with rapidly resetting cursor icon

* When setting cursor icon, if the new icon value is the same as the
  current value, no messages are sent the X server.

* X11: Cache cursor objects in XConnection

* Add changelog entry

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - On macOS, implement `run_return`.
 - On iOS, fix inverted parameter in `set_prefers_home_indicator_hidden`.
+- On X11, performance is improved when rapidly calling `Window::set_cursor_icon`.
 
 # 0.20.0 Alpha 3 (2019-08-14)
 

src/platform_impl/linux/x11/util/cursor.rs

@@ -0,0 +1,129 @@
+use crate::window::CursorIcon;
+
+use super::*;
+
+impl XConnection {
+    pub fn set_cursor_icon(&self, window: ffi::Window, cursor: Option<CursorIcon>) {
+        let cursor = *self
+            .cursor_cache
+            .lock()
+            .entry(cursor)
+            .or_insert_with(|| self.get_cursor(cursor));
+
+        self.update_cursor(window, cursor);
+    }
+
+    fn create_empty_cursor(&self) -> ffi::Cursor {
+        let data = 0;
+        let pixmap = unsafe {
+            let screen = (self.xlib.XDefaultScreen)(self.display);
+            let window = (self.xlib.XRootWindow)(self.display, screen);
+            (self.xlib.XCreateBitmapFromData)(self.display, window, &data, 1, 1)
+        };
+
+        if pixmap == 0 {
+            panic!("failed to allocate pixmap for cursor");
+        }
+
+        unsafe {
+            // We don't care about this color, since it only fills bytes
+            // in the pixmap which are not 0 in the mask.
+            let mut dummy_color = MaybeUninit::uninit();
+            let cursor = (self.xlib.XCreatePixmapCursor)(
+                self.display,
+                pixmap,
+                pixmap,
+                dummy_color.as_mut_ptr(),
+                dummy_color.as_mut_ptr(),
+                0,
+                0,
+            );
+            (self.xlib.XFreePixmap)(self.display, pixmap);
+
+            cursor
+        }
+    }
+
+    fn load_cursor(&self, name: &[u8]) -> ffi::Cursor {
+        unsafe {
+            (self.xcursor.XcursorLibraryLoadCursor)(self.display, name.as_ptr() as *const c_char)
+        }
+    }
+
+    fn load_first_existing_cursor(&self, names: &[&[u8]]) -> ffi::Cursor {
+        for name in names.iter() {
+            let xcursor = self.load_cursor(name);
+            if xcursor != 0 {
+                return xcursor;
+            }
+        }
+        0
+    }
+
+    fn get_cursor(&self, cursor: Option<CursorIcon>) -> ffi::Cursor {
+        let cursor = match cursor {
+            Some(cursor) => cursor,
+            None => return self.create_empty_cursor(),
+        };
+
+        let load = |name: &[u8]| self.load_cursor(name);
+
+        let loadn = |names: &[&[u8]]| self.load_first_existing_cursor(names);
+
+        // Try multiple names in some cases where the name
+        // differs on the desktop environments or themes.
+        //
+        // Try the better looking (or more suiting) names first.
+        match cursor {
+            CursorIcon::Alias => load(b"link\0"),
+            CursorIcon::Arrow => load(b"arrow\0"),
+            CursorIcon::Cell => load(b"plus\0"),
+            CursorIcon::Copy => load(b"copy\0"),
+            CursorIcon::Crosshair => load(b"crosshair\0"),
+            CursorIcon::Default => load(b"left_ptr\0"),
+            CursorIcon::Hand => loadn(&[b"hand2\0", b"hand1\0"]),
+            CursorIcon::Help => load(b"question_arrow\0"),
+            CursorIcon::Move => load(b"move\0"),
+            CursorIcon::Grab => loadn(&[b"openhand\0", b"grab\0"]),
+            CursorIcon::Grabbing => loadn(&[b"closedhand\0", b"grabbing\0"]),
+            CursorIcon::Progress => load(b"left_ptr_watch\0"),
+            CursorIcon::AllScroll => load(b"all-scroll\0"),
+            CursorIcon::ContextMenu => load(b"context-menu\0"),
+
+            CursorIcon::NoDrop => loadn(&[b"no-drop\0", b"circle\0"]),
+            CursorIcon::NotAllowed => load(b"crossed_circle\0"),
+
+            // Resize cursors
+            CursorIcon::EResize => load(b"right_side\0"),
+            CursorIcon::NResize => load(b"top_side\0"),
+            CursorIcon::NeResize => load(b"top_right_corner\0"),
+            CursorIcon::NwResize => load(b"top_left_corner\0"),
+            CursorIcon::SResize => load(b"bottom_side\0"),
+            CursorIcon::SeResize => load(b"bottom_right_corner\0"),
+            CursorIcon::SwResize => load(b"bottom_left_corner\0"),
+            CursorIcon::WResize => load(b"left_side\0"),
+            CursorIcon::EwResize => load(b"h_double_arrow\0"),
+            CursorIcon::NsResize => load(b"v_double_arrow\0"),
+            CursorIcon::NwseResize => loadn(&[b"bd_double_arrow\0", b"size_bdiag\0"]),
+            CursorIcon::NeswResize => loadn(&[b"fd_double_arrow\0", b"size_fdiag\0"]),
+            CursorIcon::ColResize => loadn(&[b"split_h\0", b"h_double_arrow\0"]),
+            CursorIcon::RowResize => loadn(&[b"split_v\0", b"v_double_arrow\0"]),
+
+            CursorIcon::Text => loadn(&[b"text\0", b"xterm\0"]),
+            CursorIcon::VerticalText => load(b"vertical-text\0"),
+
+            CursorIcon::Wait => load(b"watch\0"),
+
+            CursorIcon::ZoomIn => load(b"zoom-in\0"),
+            CursorIcon::ZoomOut => load(b"zoom-out\0"),
+        }
+    }
+
+    fn update_cursor(&self, window: ffi::Window, cursor: ffi::Cursor) {
+        unsafe {
+            (self.xlib.XDefineCursor)(self.display, window, cursor);
+
+            self.flush_requests().expect("Failed to set the cursor");
+        }
+    }
+}

src/platform_impl/linux/x11/util/mod.rs

@@ -3,6 +3,7 @@
 
 mod atom;
 mod client_msg;
+mod cursor;
 mod format;
 mod geometry;
 mod hint;

src/platform_impl/linux/x11/window.rs

@@ -4,7 +4,7 @@ use std::{
     collections::HashSet,
     env,
     ffi::CString,
-    mem::{self, MaybeUninit},
+    mem::{self, replace, MaybeUninit},
     os::raw::*,
     path::Path,
     ptr, slice,
@@ -1124,131 +1124,14 @@ impl UnownedWindow {
         unsafe { (self.xconn.xlib_xcb.XGetXCBConnection)(self.xconn.display) as *mut _ }
     }
 
-    fn load_cursor(&self, name: &[u8]) -> ffi::Cursor {
-        unsafe {
-            (self.xconn.xcursor.XcursorLibraryLoadCursor)(
-                self.xconn.display,
-                name.as_ptr() as *const c_char,
-            )
-        }
-    }
-
-    fn load_first_existing_cursor(&self, names: &[&[u8]]) -> ffi::Cursor {
-        for name in names.iter() {
-            let xcursor = self.load_cursor(name);
-            if xcursor != 0 {
-                return xcursor;
-            }
-        }
-        0
-    }
-
-    fn get_cursor(&self, cursor: CursorIcon) -> ffi::Cursor {
-        let load = |name: &[u8]| self.load_cursor(name);
-
-        let loadn = |names: &[&[u8]]| self.load_first_existing_cursor(names);
-
-        // Try multiple names in some cases where the name
-        // differs on the desktop environments or themes.
-        //
-        // Try the better looking (or more suiting) names first.
-        match cursor {
-            CursorIcon::Alias => load(b"link\0"),
-            CursorIcon::Arrow => load(b"arrow\0"),
-            CursorIcon::Cell => load(b"plus\0"),
-            CursorIcon::Copy => load(b"copy\0"),
-            CursorIcon::Crosshair => load(b"crosshair\0"),
-            CursorIcon::Default => load(b"left_ptr\0"),
-            CursorIcon::Hand => loadn(&[b"hand2\0", b"hand1\0"]),
-            CursorIcon::Help => load(b"question_arrow\0"),
-            CursorIcon::Move => load(b"move\0"),
-            CursorIcon::Grab => loadn(&[b"openhand\0", b"grab\0"]),
-            CursorIcon::Grabbing => loadn(&[b"closedhand\0", b"grabbing\0"]),
-            CursorIcon::Progress => load(b"left_ptr_watch\0"),
-            CursorIcon::AllScroll => load(b"all-scroll\0"),
-            CursorIcon::ContextMenu => load(b"context-menu\0"),
-
-            CursorIcon::NoDrop => loadn(&[b"no-drop\0", b"circle\0"]),
-            CursorIcon::NotAllowed => load(b"crossed_circle\0"),
-
-            // Resize cursors
-            CursorIcon::EResize => load(b"right_side\0"),
-            CursorIcon::NResize => load(b"top_side\0"),
-            CursorIcon::NeResize => load(b"top_right_corner\0"),
-            CursorIcon::NwResize => load(b"top_left_corner\0"),
-            CursorIcon::SResize => load(b"bottom_side\0"),
-            CursorIcon::SeResize => load(b"bottom_right_corner\0"),
-            CursorIcon::SwResize => load(b"bottom_left_corner\0"),
-            CursorIcon::WResize => load(b"left_side\0"),
-            CursorIcon::EwResize => load(b"h_double_arrow\0"),
-            CursorIcon::NsResize => load(b"v_double_arrow\0"),
-            CursorIcon::NwseResize => loadn(&[b"bd_double_arrow\0", b"size_bdiag\0"]),
-            CursorIcon::NeswResize => loadn(&[b"fd_double_arrow\0", b"size_fdiag\0"]),
-            CursorIcon::ColResize => loadn(&[b"split_h\0", b"h_double_arrow\0"]),
-            CursorIcon::RowResize => loadn(&[b"split_v\0", b"v_double_arrow\0"]),
-
-            CursorIcon::Text => loadn(&[b"text\0", b"xterm\0"]),
-            CursorIcon::VerticalText => load(b"vertical-text\0"),
-
-            CursorIcon::Wait => load(b"watch\0"),
-
-            CursorIcon::ZoomIn => load(b"zoom-in\0"),
-            CursorIcon::ZoomOut => load(b"zoom-out\0"),
-        }
-    }
-
-    fn update_cursor(&self, cursor: ffi::Cursor) {
-        unsafe {
-            (self.xconn.xlib.XDefineCursor)(self.xconn.display, self.xwindow, cursor);
-            if cursor != 0 {
-                (self.xconn.xlib.XFreeCursor)(self.xconn.display, cursor);
-            }
-            self.xconn
-                .flush_requests()
-                .expect("Failed to set or free the cursor");
-        }
-    }
-
     #[inline]
     pub fn set_cursor_icon(&self, cursor: CursorIcon) {
-        *self.cursor.lock() = cursor;
-        if *self.cursor_visible.lock() {
-            self.update_cursor(self.get_cursor(cursor));
+        let old_cursor = replace(&mut *self.cursor.lock(), cursor);
+        if cursor != old_cursor && *self.cursor_visible.lock() {
+            self.xconn.set_cursor_icon(self.xwindow, Some(cursor));
         }
     }
 
-    // TODO: This could maybe be cached. I don't think it's worth
-    // the complexity, since cursor changes are not so common,
-    // and this is just allocating a 1x1 pixmap...
-    fn create_empty_cursor(&self) -> Option<ffi::Cursor> {
-        let data = 0;
-        let pixmap = unsafe {
-            (self.xconn.xlib.XCreateBitmapFromData)(self.xconn.display, self.xwindow, &data, 1, 1)
-        };
-        if pixmap == 0 {
-            // Failed to allocate
-            return None;
-        }
-
-        let cursor = unsafe {
-            // We don't care about this color, since it only fills bytes
-            // in the pixmap which are not 0 in the mask.
-            let mut dummy_color = MaybeUninit::uninit();
-            let cursor = (self.xconn.xlib.XCreatePixmapCursor)(
-                self.xconn.display,
-                pixmap,
-                pixmap,
-                dummy_color.as_mut_ptr(),
-                dummy_color.as_mut_ptr(),
-                0,
-                0,
-            );
-            (self.xconn.xlib.XFreePixmap)(self.xconn.display, pixmap);
-            cursor
-        };
-        Some(cursor)
-    }
-
     #[inline]
     pub fn set_cursor_grab(&self, grab: bool) -> Result<(), ExternalError> {
         let mut grabbed_lock = self.cursor_grabbed.lock();
@@ -1318,14 +1201,13 @@ impl UnownedWindow {
             return;
         }
         let cursor = if visible {
-            self.get_cursor(*self.cursor.lock())
+            Some(*self.cursor.lock())
         } else {
-            self.create_empty_cursor()
-                .expect("Failed to create empty cursor")
+            None
         };
         *visible_lock = visible;
         drop(visible_lock);
-        self.update_cursor(cursor);
+        self.xconn.set_cursor_icon(self.xwindow, cursor);
     }
 
     #[inline]

src/platform_impl/linux/x11/xdisplay.rs

@@ -1,8 +1,10 @@
-use std::{error::Error, fmt, os::raw::c_int, ptr};
+use std::{collections::HashMap, error::Error, fmt, os::raw::c_int, ptr};
 
 use libc;
 use parking_lot::Mutex;
 
+use crate::window::CursorIcon;
+
 use super::ffi;
 
 /// A connection to an X server.
@@ -19,6 +21,7 @@ pub struct XConnection {
     pub display: *mut ffi::Display,
     pub x11_fd: c_int,
     pub latest_error: Mutex<Option<XError>>,
+    pub cursor_cache: Mutex<HashMap<Option<CursorIcon>, ffi::Cursor>>,
 }
 
 unsafe impl Send for XConnection {}
@@ -64,6 +67,7 @@ impl XConnection {
             display,
             x11_fd: fd,
             latest_error: Mutex::new(None),
+            cursor_cache: Default::default(),
         })
     }