Fix PTY performance regressions

The patch 9e7655e introduced some changes which improved rendering with
very dense grids, but the automatic benchmarks indicated a slight
performance difference in the `dense_cells` benchmark.

Caching the terminal lock between iterations rather than always calling
`try_lock` resolves that issue.

While breaking early in the `WouldBlock` case with `unprocessed != 0`
does also help resolve these issues, it shows some more significant
fluctuations. Combining both fixes does not help.

Additionally on Windows receiving `Ok(0)` from the PTY will also occur
instead of a `WouldBlock` error, so handling that fixes freezing on
Windows.

Fixes #5305.

.builds/freebsd.yml

@@ -8,6 +8,7 @@ packages:
   - x11-fonts/fontconfig
   - x11-fonts/dejavu
   - x11/libxcb
+  - x11/libxkbcommon
 
 sources:
   - https://github.com/alacritty/alacritty

.builds/linux.yml

@@ -7,6 +7,7 @@ packages:
   - freetype2
   - fontconfig
   - libxcb
+  - libxkbcommon
 
 sources:
   - https://github.com/alacritty/alacritty

Cargo.lock

@@ -143,12 +143,6 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0d8c1fef690941d3e7788d328517591fecc684c084084702d6ff1641e993699a"
 
-[[package]]
-name = "byteorder"
-version = "1.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "14c189c53d098945499cdfa7ecc63567cf3886b3332b312a5b4585d8d3a6a610"
-
 [[package]]
 name = "calloop"
 version = "0.6.5"
@@ -161,9 +155,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.0.67"
+version = "1.0.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e3c69b077ad434294d3ce9f1f6143a2a4b89a8a2d54ef813d85003a4fd1137fd"
+checksum = "4a72c244c1ff497a746a7e1fb3d14bd08420ecda70c8f25c7112f2781652d787"
 
 [[package]]
 name = "cfg-if"
@@ -523,9 +517,9 @@ dependencies = [
 
 [[package]]
 name = "embed-resource"
-version = "1.6.2"
+version = "1.6.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d0ea6debf1262982d24274dc85f3374b42534df140897c25cea86b81e017d470"
+checksum = "45de30eb317b4cd3882ee16623cb3004e5fb99a8f4cd40097cadf61efbc54adc"
 dependencies = [
  "cc",
  "vswhom",
@@ -661,9 +655,9 @@ checksum = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
 
 [[package]]
 name = "getrandom"
-version = "0.2.2"
+version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c9495705279e7140bf035dde1f6e750c162df8b625267cd52cc44e0b156732c8"
+checksum = "7fcd999463524c52659517fe2cea98493cfe485d10565e7b0fb07dbba7ad2753"
 dependencies = [
  "cfg-if 1.0.0",
  "libc",
@@ -755,9 +749,9 @@ dependencies = [
 
 [[package]]
 name = "hermit-abi"
-version = "0.1.18"
+version = "0.1.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "322f4de77956e22ed0e5032c359a0f1273f1f7f0d79bfa3b8ffbc730d7fbcc5c"
+checksum = "62b467343b94ba476dcb2500d242dadbb39557df889310ac77c5d99100aaac33"
 dependencies = [
  "libc",
 ]
@@ -854,9 +848,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.94"
+version = "0.2.98"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18794a8ad5b29321f790b55d93dfba91e125cb1a9edbd4f8e3150acc771c1a5e"
+checksum = "320cfe77175da3a483efed4bc0adc1968ca050b098ce4f2f1c13a56626128790"
 
 [[package]]
 name = "libloading"
@@ -920,9 +914,9 @@ checksum = "60302e4db3a61da70c0cb7991976248362f30319e88850c487b9b95bbf059e00"
 
 [[package]]
 name = "memchr"
-version = "2.4.0"
+version = "2.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b16bd47d9e329435e309c58469fe0791c2d0d1ba96ec0954152a5ae2b04387dc"
+checksum = "0ee1c47aaa256ecabcaea351eae4a9b01ef39ed810004e298d2511ed284b1525"
 
 [[package]]
 name = "memmap2"
@@ -933,6 +927,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "memmap2"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "723e3ebdcdc5c023db1df315364573789f8857c11b631a2fdfad7c00f5c046b4"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.3.7"
@@ -1088,9 +1091,9 @@ dependencies = [
 
 [[package]]
 name = "nom"
-version = "6.1.2"
+version = "6.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e7413f999671bd4745a7b624bd370a569fb6bc574b23c83a3c5ed2e453f3d5e2"
+checksum = "9c5c51b9083a3c620fa67a2a635d1ce7d95b897e957d6b28ff9a5da960a103a6"
 dependencies = [
  "memchr",
  "version_check",
@@ -1098,9 +1101,9 @@ dependencies = [
 
 [[package]]
 name = "notify"
-version = "4.0.16"
+version = "4.0.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2599080e87c9bd051ddb11b10074f4da7b1223298df65d4c2ec5bcf309af1533"
+checksum = "ae03c8c853dba7bfd23e571ff0cff7bc9dceb40a4cd684cd1681824183f45257"
 dependencies = [
  "bitflags",
  "filetime",
@@ -1167,9 +1170,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.7.2"
+version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af8b08b04175473088b46763e51ee54da5f9a164bc162f615b91bc179dbf15a3"
+checksum = "692fcb63b64b1758029e0a96ee63e049ce8c5948587f2f7208df04625e5f6b56"
 
 [[package]]
 name = "osmesa-sys"
@@ -1248,9 +1251,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.26"
+version = "1.0.27"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a152013215dca273577e18d2bf00fa862b89b24169fb78c4c95aeb07992c9cec"
+checksum = "f0d8caf72986c1a598726adc988bb5984792ef84f5ee5aa50209145ee8077038"
 dependencies = [
  "unicode-xid",
 ]
@@ -1275,9 +1278,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.2.7"
+version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "85dd92e586f7355c633911e11f77f3d12f04b1b1bd76a198bd34ae3af8341ef2"
+checksum = "5ab49abadf3f9e1c4bc499e8845e152ad87d2ad2d30371841171169e9d75feee"
 dependencies = [
  "bitflags",
 ]
@@ -1294,19 +1297,18 @@ dependencies = [
 
 [[package]]
 name = "regex-automata"
-version = "0.1.9"
+version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ae1ded71d66a4a97f5e961fd0cb25a5f366a42a41570d16a763a69c092c26ae4"
+checksum = "6c230d73fb8d8c1b9c0b3135c5142a8acee3a0558fb8db5cf1cb65f8d7862132"
 dependencies = [
- "byteorder",
  "regex-syntax",
 ]
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.24"
+version = "0.6.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "00efb87459ba4f6fb2169d20f68565555688e1250ee6825cdf6254f8b48fafb2"
+checksum = "f497285884f3fcff424ffc933e56d7cbca511def0c9831a7f9b5f6153e3cc89b"
 
 [[package]]
 name = "rusttype"
@@ -1347,18 +1349,18 @@ checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
 [[package]]
 name = "serde"
-version = "1.0.125"
+version = "1.0.126"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "558dc50e1a5a5fa7112ca2ce4effcb321b0300c0d4ccf0776a9f60cd89031171"
+checksum = "ec7505abeacaec74ae4778d9d9328fe5a5d04253220a85c4ee022239fc996d03"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.125"
+version = "1.0.126"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b093b7a2bb58203b5da3056c05b4ec1fed827dcfdb37347a8841695263b3d06d"
+checksum = "963a7dbc9895aeac7ac90e74f34a5d5261828f79df35cbed41e10189d3804d43"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1432,9 +1434,9 @@ dependencies = [
 
 [[package]]
 name = "signal-hook-registry"
-version = "1.3.0"
+version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "16f1d0fef1604ba8f7a073c7e701f213e056707210e9020af4528e0101ce11a6"
+checksum = "e51e73328dc4ac0c7ccbda3a494dfa03df1de2f46018127f60c693f2648455b0"
 dependencies = [
  "libc",
 ]
@@ -1463,7 +1465,7 @@ dependencies = [
  "dlib 0.4.2",
  "lazy_static",
  "log",
- "memmap2",
+ "memmap2 0.1.0",
  "nix 0.18.0",
  "wayland-client",
  "wayland-cursor",
@@ -1471,12 +1473,29 @@ dependencies = [
 ]
 
 [[package]]
-name = "smithay-clipboard"
+name = "smithay-client-toolkit"
-version = "0.6.3"
+version = "0.14.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "06384dfaf645908220d976ae24ed39f6cf92efecb0225ea0a948e403014de527"
+checksum = "ec783683499a2cfc85b6df3d04f83b1907b5cbd98a1aed44667dbdf1eac4e64c"
 dependencies = [
- "smithay-client-toolkit",
+ "bitflags",
+ "dlib 0.5.0",
+ "lazy_static",
+ "log",
+ "memmap2 0.2.3",
+ "nix 0.20.0",
+ "wayland-client",
+ "wayland-cursor",
+ "wayland-protocols",
+]
+
+[[package]]
+name = "smithay-clipboard"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "986c5b4a7bd4f50d4c51f81f844745535cb488360f9cf63293780b109b9295f3"
+dependencies = [
+ "smithay-client-toolkit 0.14.0",
  "wayland-client",
 ]
 
@@ -1500,9 +1519,9 @@ checksum = "6446ced80d6c486436db5c078dde11a9f73d42b57fb273121e160b84f63d894c"
 
 [[package]]
 name = "syn"
-version = "1.0.71"
+version = "1.0.73"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ad184cc9470f9117b2ac6817bfe297307418819ba40552f9b3846f05c33d5373"
+checksum = "f71489ff30030d2ae598524f61326b902466f72a0fb1a8564c001cc63425bcc7"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1520,18 +1539,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.24"
+version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e0f4a65597094d4483ddaed134f409b2cb7c1beccf25201a9f73c719254fa98e"
+checksum = "93119e4feac1cbe6c798c34d3a53ea0026b0b1de6a120deef895137c0529bfe2"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.24"
+version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7765189610d8241a44529806d6fd1f2e0a08734313a35d5b3a556f92b381f3c0"
+checksum = "060d69a0afe7796bf42e9e2ff91f5ee691fb15c53d38b4b62a9a53eb23164745"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1652,9 +1671,9 @@ checksum = "fd6fbd9a79829dd1ad0cc20627bf1ed606756a7f77edff7b66b7064f9cb327c6"
 
 [[package]]
 name = "wayland-client"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "06ca44d86554b85cf449f1557edc6cc7da935cc748c8e4bf1c507cbd43bae02c"
+checksum = "e3ab332350e502f159382201394a78e3cc12d0f04db863429260164ea40e0355"
 dependencies = [
  "bitflags",
  "downcast-rs",
@@ -1668,9 +1687,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-commons"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8bd75ae380325dbcff2707f0cd9869827ea1d2d6d534cff076858d3f0460fd5a"
+checksum = "a21817947c7011bbd0a27e11b17b337bfd022e8544b071a2641232047966fbda"
 dependencies = [
  "nix 0.20.0",
  "once_cell",
@@ -1680,9 +1699,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-cursor"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b37e5455ec72f5de555ec39b5c3704036ac07c2ecd50d0bffe02d5fe2d4e65ab"
+checksum = "be610084edd1586d45e7bdd275fe345c7c1873598caa464c4fb835dee70fa65a"
 dependencies = [
  "nix 0.20.0",
  "wayland-client",
@@ -1691,9 +1710,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-egl"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9461a67930ec16da7a4fd8b50e9ffa23f4417240b43ec84008bd1b2c94421c94"
+checksum = "99ba1ab1e18756b23982d36f08856d521d7df45015f404a2d7c4f0b2d2f66956"
 dependencies = [
  "wayland-client",
  "wayland-sys",
@@ -1701,9 +1720,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-protocols"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "95df3317872bcf9eec096c864b69aa4769a1d5d6291a5b513f8ba0af0efbd52c"
+checksum = "286620ea4d803bacf61fa087a4242ee316693099ee5a140796aaba02b29f861f"
 dependencies = [
  "bitflags",
  "wayland-client",
@@ -1713,9 +1732,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-scanner"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "389d680d7bd67512dc9c37f39560224327038deb0f0e8d33f870900441b68720"
+checksum = "ce923eb2deb61de332d1f356ec7b6bf37094dc5573952e1c8936db03b54c03f1"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1724,9 +1743,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-sys"
-version = "0.28.5"
+version = "0.28.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2907bd297eef464a95ba9349ea771611771aa285b932526c633dc94d5400a8e2"
+checksum = "d841fca9aed7febf9bed2e9796c49bf58d4152ceda8ac949ebe00868d8f0feb8"
 dependencies = [
  "dlib 0.5.0",
  "lazy_static",
@@ -1802,7 +1821,7 @@ dependencies = [
  "percent-encoding",
  "raw-window-handle",
  "serde",
- "smithay-client-toolkit",
+ "smithay-client-toolkit 0.12.3",
  "wayland-client",
  "winapi 0.3.9",
  "x11-dl",
@@ -1810,9 +1829,9 @@ dependencies = [
 
 [[package]]
 name = "winreg"
-version = "0.8.0"
+version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d107f8c6e916235c4c01cabb3e8acf7bea8ef6a63ca2e7fa0527c049badfc48c"
+checksum = "16cdb3898397cf7f624c294948669beafaeebc5577d5ec53d0afb76633593597"
 dependencies = [
  "winapi 0.3.9",
 ]
@@ -1838,9 +1857,9 @@ dependencies = [
 
 [[package]]
 name = "x11-clipboard"
-version = "0.5.1"
+version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e5e937afd03b64b7be4f959cc044e09260a47241b71e56933f37db097bf7859d"
+checksum = "b397ace6e980510de59a4fe3d4c758dffab231d6d747ce9fa1aba6b6035d5f32"
 dependencies = [
  "xcb",
 ]

alacritty_terminal/src/event_loop.rs

@@ -221,10 +221,13 @@ where
 
         // Reserve the next terminal lock for PTY reading.
         let _terminal_lease = Some(self.terminal.lease());
+        let mut terminal = None;
 
         loop {
             // Read from the PTY.
             match self.pty.reader().read(&mut buf[unprocessed..]) {
+                // This is received on Windows/macOS when no more data is readable from the PTY.
+                Ok(0) if unprocessed == 0 => break,
                 Ok(got) => unprocessed += got,
                 Err(err) => match err.kind() {
                     ErrorKind::Interrupted | ErrorKind::WouldBlock => {
@@ -238,11 +241,14 @@ where
             }
 
             // Attempt to lock the terminal.
-            let mut terminal = match self.terminal.try_lock_unfair() {
+            let terminal = match &mut terminal {
-                // Force block if we are at the buffer size limit.
-                None if unprocessed >= READ_BUFFER_SIZE => self.terminal.lock_unfair(),
-                None => continue,
                 Some(terminal) => terminal,
+                None => terminal.insert(match self.terminal.try_lock_unfair() {
+                    // Force block if we are at the buffer size limit.
+                    None if unprocessed >= READ_BUFFER_SIZE => self.terminal.lock_unfair(),
+                    None => continue,
+                    Some(terminal) => terminal,
+                }),
             };
 
             // Write a copy of the bytes to the ref test file.
@@ -252,7 +258,7 @@ where
 
             // Parse the incoming bytes.
             for byte in &buf[..unprocessed] {
-                state.parser.advance(&mut *terminal, *byte);
+                state.parser.advance(&mut **terminal, *byte);
             }
 
             processed += unprocessed;
@@ -425,3 +431,32 @@ where
         })
     }
 }
+
+trait OptionInsert {
+    type T;
+    fn insert(&mut self, value: Self::T) -> &mut Self::T;
+}
+
+// TODO: Remove when MSRV is >= 1.53.0.
+//
+/// Trait implementation to support Rust version < 1.53.0.
+///
+/// This is taken [from STD], further license information can be found in the [rust-lang/rust
+/// repository].
+///
+///
+/// [from STD]: https://github.com/rust-lang/rust/blob/6e0b554619a3bb7e75b3334e97f191af20ef5d76/library/core/src/option.rs#L829-L858
+/// [rust-lang/rust repository]: https://github.com/rust-lang/rust/blob/master/LICENSE-MIT
+impl<T> OptionInsert for Option<T> {
+    type T = T;
+
+    fn insert(&mut self, value: T) -> &mut T {
+        *self = Some(value);
+
+        match self {
+            Some(v) => v,
+            // SAFETY: the code above just filled the option
+            None => unsafe { std::hint::unreachable_unchecked() },
+        }
+    }
+}