1 files changed, 93 insertions, 0 deletions
diff --git a/compiler/rustc_errors/src/lock.rs b/compiler/rustc_errors/src/lock.rs
new file mode 100644
index 000000000..a73472021
--- /dev/null
+++ b/compiler/rustc_errors/src/lock.rs
@@ -0,0 +1,93 @@
+//! Bindings to acquire a global named lock.
+//!
+//! This is intended to be used to synchronize multiple compiler processes to
+//! ensure that we can output complete errors without interleaving on Windows.
+//! Note that this is currently only needed for allowing only one 32-bit MSVC
+//! linker to execute at once on MSVC hosts, so this is only implemented for
+//! `cfg(windows)`. Also note that this may not always be used on Windows,
+//! only when targeting 32-bit MSVC.
+//!
+//! For more information about why this is necessary, see where this is called.
+
+use std::any::Any;
+
+#[cfg(windows)]
+pub fn acquire_global_lock(name: &str) -> Box<dyn Any> {
+    use std::ffi::CString;
+    use std::io;
+
+    use winapi::shared::ntdef::HANDLE;
+    use winapi::um::handleapi::CloseHandle;
+    use winapi::um::synchapi::{CreateMutexA, ReleaseMutex, WaitForSingleObject};
+    use winapi::um::winbase::{INFINITE, WAIT_ABANDONED, WAIT_OBJECT_0};
+
+    struct Handle(HANDLE);
+
+    impl Drop for Handle {
+        fn drop(&mut self) {
+            unsafe {
+                CloseHandle(self.0);
+            }
+        }
+    }
+
+    struct Guard(Handle);
+
+    impl Drop for Guard {
+        fn drop(&mut self) {
+            unsafe {
+                ReleaseMutex((self.0).0);
+            }
+        }
+    }
+
+    let cname = CString::new(name).unwrap();
+    unsafe {
+        // Create a named mutex, with no security attributes and also not
+        // acquired when we create it.
+        //
+        // This will silently create one if it doesn't already exist, or it'll
+        // open up a handle to one if it already exists.
+        let mutex = CreateMutexA(std::ptr::null_mut(), 0, cname.as_ptr());
+        if mutex.is_null() {
+            panic!(
+                "failed to create global mutex named `{}`: {}",
+                name,
+                io::Error::last_os_error()
+            );
+        }
+        let mutex = Handle(mutex);
+
+        // Acquire the lock through `WaitForSingleObject`.
+        //
+        // A return value of `WAIT_OBJECT_0` means we successfully acquired it.
+        //
+        // A return value of `WAIT_ABANDONED` means that the previous holder of
+        // the thread exited without calling `ReleaseMutex`. This can happen,
+        // for example, when the compiler crashes or is interrupted via ctrl-c
+        // or the like. In this case, however, we are still transferred
+        // ownership of the lock so we continue.
+        //
+        // If an error happens.. well... that's surprising!
+        match WaitForSingleObject(mutex.0, INFINITE) {
+            WAIT_OBJECT_0 | WAIT_ABANDONED => {}
+            code => {
+                panic!(
+                    "WaitForSingleObject failed on global mutex named \
+                        `{}`: {} (ret={:x})",
+                    name,
+                    io::Error::last_os_error(),
+                    code
+                );
+            }
+        }
+
+        // Return a guard which will call `ReleaseMutex` when dropped.
+        Box::new(Guard(mutex))
+    }
+}
+
+#[cfg(not(windows))]
+pub fn acquire_global_lock(_name: &str) -> Box<dyn Any> {
+    Box::new(())
+}