Bug 1637998 - Hook up loom for concurrency testingting of wgpu r=groves

Differential Revision: https://phabricator.services.mozilla.com/D77159

gfx/wgpu/Cargo.lock

@@ -357,6 +357,19 @@ dependencies = [
  "byteorder",
 ]
 
+[[package]]
+name = "generator"
+version = "0.6.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "caaa160efb38ce00acbe4450d41a103fb3d2acdb17ff09a7cf38f3ac26af0738"
+dependencies = [
+ "cc",
+ "libc",
+ "log",
+ "rustc_version",
+ "winapi 0.3.8",
+]
+
 [[package]]
 name = "gfx-auxil"
 version = "0.3.0"
@@ -622,6 +635,17 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "loom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ecc775857611e1df29abba5c41355cdf540e7e9d4acfdf0f355eefee82330b7"
+dependencies = [
+ "cfg-if",
+ "generator",
+ "scoped-tls",
+]
+
 [[package]]
 name = "mach"
 version = "0.2.3"
@@ -985,6 +1009,15 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
+dependencies = [
+ "semver",
+]
+
 [[package]]
 name = "rusttype"
 version = "0.7.9"
@@ -1014,12 +1047,33 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "scoped-tls"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "332ffa32bf586782a3efaeb58f127980944bbc8c4d6913a86107ac2a5ab24b28"
+
 [[package]]
 name = "scopeguard"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+dependencies = [
+ "semver-parser",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+
 [[package]]
 name = "serde"
 version = "1.0.106"
@@ -1321,6 +1375,7 @@ dependencies = [
  "gfx-hal",
  "gfx-memory",
  "log",
+ "loom",
  "parking_lot",
  "peek-poke",
  "raw-window-handle",

gfx/wgpu/wgpu-core/Cargo.toml

@@ -60,3 +60,6 @@ gfx-backend-vulkan = { version = "0.5" }
 
 [target.'cfg(any(target_os = "linux", target_os = "macos", target_os = "windows", target_os = "dragonfly", target_os = "freebsd"))'.dependencies]
 battery = { version = "0.7", optional = true }
+
+[dev-dependencies]
+loom = "0.3"

gfx/wgpu/wgpu-core/src/lib.rs

@@ -39,11 +39,14 @@ mod track;
 
 pub use hal::pso::read_spirv;
 
-use std::{
-    os::raw::c_char,
-    ptr,
-    sync::atomic::{AtomicUsize, Ordering},
-};
+#[cfg(test)]
+use loom::sync::atomic;
+#[cfg(not(test))]
+use std::sync::atomic;
+
+use atomic::{AtomicUsize, Ordering};
+
+use std::{os::raw::c_char, ptr};
 
 type SubmissionIndex = usize;
 type Index = u32;
@@ -64,6 +67,27 @@ impl RefCount {
     fn load(&self) -> usize {
         unsafe { self.0.as_ref() }.load(Ordering::Acquire)
     }
+
+    /// This works like `std::mem::drop`, except that it returns a boolean which is true if and only
+    /// if we deallocated the underlying memory, i.e. if this was the last clone of this `RefCount`
+    /// to be dropped. This is useful for loom testing because it allows us to verify that we
+    /// deallocated the underlying memory exactly once.
+    #[cfg(test)]
+    fn rich_drop_outer(self) -> bool {
+        unsafe { std::mem::ManuallyDrop::new(self).rich_drop_inner() }
+    }
+
+    /// This function exists to allow `Self::rich_drop_outer` and `Drop::drop` to share the same
+    /// logic. To use this safely from outside of `Drop::drop`, the calling function must move
+    /// `Self` into a `ManuallyDrop`.
+    unsafe fn rich_drop_inner(&mut self) -> bool {
+        if self.0.as_ref().fetch_sub(1, Ordering::Relaxed) == 1 {
+            let _ = Box::from_raw(self.0.as_ptr());
+            true
+        } else {
+            false
+        }
+    }
 }
 
 impl Clone for RefCount {
@@ -76,12 +100,34 @@ impl Clone for RefCount {
 
 impl Drop for RefCount {
     fn drop(&mut self) {
-        if unsafe { self.0.as_ref() }.fetch_sub(1, Ordering::Relaxed) == 1 {
-            let _ = unsafe { Box::from_raw(self.0.as_ptr()) };
+        unsafe {
+            self.rich_drop_inner();
         }
     }
 }
 
+#[cfg(test)]
+#[test]
+fn loom() {
+    loom::model(move || {
+        let bx = Box::new(AtomicUsize::new(1));
+        let ref_count_main = ptr::NonNull::new(Box::into_raw(bx)).map(RefCount).unwrap();
+        let ref_count_spawned = ref_count_main.clone();
+
+        let join_handle = loom::thread::spawn(move || {
+            let _ = ref_count_spawned.clone();
+            ref_count_spawned.rich_drop_outer()
+        });
+
+        let dropped_in_main = ref_count_main.rich_drop_outer();
+        let dropped_in_spawned = join_handle.join().unwrap();
+        assert_ne!(
+            dropped_in_main, dropped_in_spawned,
+            "must drop exactly once"
+        );
+    });
+}
+
 #[derive(Debug)]
 struct LifeGuard {
     ref_count: Option<RefCount>,