rustc: Globally lock link.exe on 32-bit MSVC

src/librustc_trans/back/link.rs

@@ -658,6 +658,42 @@ fn link_natively(sess: &Session, dylib: bool,
     // May have not found libraries in the right formats.
     sess.abort_if_errors();
 
+    // Ensure that when we target 32-bit MSVC from a Windows host that we only
+    // invoke at most one linker at a time.
+    //
+    // Well gee "whomever wrote this comment", isn't that bad! It sure is
+    // "whomever is reading this comment"!
+    //
+    // The backstory on this "weird linker hack #3194" is that awhile back we
+    // started seeing a lot of spurious failures on the 32-bit MSVC bot.
+    // Specifically, rust-lang/rust#33145 started tracking that, and the issue
+    // was that the linker was complaining about weird PDB RPCs. Searching
+    // around seemed to turn up that this is related to mspdbsrv.exe not exactly
+    // being robust in the face of things like **being run in parallel**.
+    //
+    // Some investigation turned up that this is indeed the case. Crucially, the
+    // linker would fail if run in parallel. This was tested by just writing a
+    // script that ran `rustc foo.rs` in two different directories for two
+    // differently-named `foo.rs` files each containing `fn main() {}`. When
+    // targeting 32-bit MSVC the linker would occasionally fail with a similar
+    // error as in the issue mentioned above.
+    //
+    // So all in all, that means if we're targeting 32-bit MSVC we can't
+    // actually run the linker in parallel! Well isn't that just a joy. To work
+    // around this we acquire a global IPC lock for our platform in that case to
+    // ensure that we only run one linker at a time.
+    //
+    // Note that the `acquire_global_lock` function is only implemented on
+    // Windows, it's just a noop for other platforms. Hopefully the linker for
+    // 32-bit MSVC can actually run in parallel when ported to a platform other
+    // than Windows!
+    let _lock = if sess.target.target.options.is_like_msvc &&
+                   sess.target.target.target_pointer_width == "32" {
+        Some(msvc::acquire_global_lock("__rustc_32_msvc_glorious_hack"))
+    } else {
+        None
+    };
+
     // Invoke the system linker
     info!("{:?}", &cmd);
     let prog = time(sess.time_passes(), "running linker", || cmd.output());

src/librustc_trans/back/msvc/lock.rs

@@ -0,0 +1,112 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Bindings to acquire a global named lock.
+//!
+//! This is intended to be used to synchronize multiple compiler processes to
+//! ensure that only one can proceed during certain phases. 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)]
+#[allow(bad_style)]
+pub fn acquire_global_lock(name: &str) -> Box<Any> {
+    use std::ffi::CString;
+    use std::io;
+
+    type LPSECURITY_ATTRIBUTES = *mut u8;
+    type BOOL = i32;
+    type LPCSTR = *const u8;
+    type HANDLE = *mut u8;
+    type DWORD = u32;
+
+    const INFINITE: DWORD = !0;
+    const WAIT_OBJECT_0: DWORD = 0;
+    const WAIT_ABANDONED: DWORD = 0x00000080;
+
+    extern "system" {
+        fn CreateMutexA(lpMutexAttributes: LPSECURITY_ATTRIBUTES,
+                        bInitialOwner: BOOL,
+                        lpName: LPCSTR) -> HANDLE;
+        fn WaitForSingleObject(hHandle: HANDLE,
+                               dwMilliseconds: DWORD) -> DWORD;
+        fn ReleaseMutex(hMutex: HANDLE) -> BOOL;
+        fn CloseHandle(hObject: HANDLE) -> BOOL;
+    }
+
+    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(0 as *mut _, 0, cname.as_ptr() as *const u8);
+        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(unix)]
+pub fn acquire_global_lock(_name: &str) -> Box<Any> {
+    Box::new(())
+}

src/librustc_trans/back/msvc/mod.rs

@@ -34,6 +34,9 @@
 #[cfg(windows)]
 mod registry;
 
+mod lock;
+pub use self::lock::acquire_global_lock;
+
 #[cfg(windows)]
 mod platform {
     use std::env;