src/librustc_errors/lock.rs

   1 //! Bindings to acquire a global named lock.
   2 //!
   3 //! This is intended to be used to synchronize multiple compiler processes to
   4 //! ensure that we can output complete errors without interleaving on Windows.
   5 //! Note that this is currently only needed for allowing only one 32-bit MSVC
   6 //! linker to execute at once on MSVC hosts, so this is only implemented for
   7 //! `cfg(windows)`. Also note that this may not always be used on Windows,
   8 //! only when targeting 32-bit MSVC.
   9 //!
  10 //! For more information about why this is necessary, see where this is called.
  11
  12 use std::any::Any;
  13
  14 #[cfg(windows)]
  15 #[allow(nonstandard_style)]
  16 pub fn acquire_global_lock(name: &str) -> Box<dyn Any> {
  17     use std::ffi::CString;
  18     use std::io;
  19
  20     type LPSECURITY_ATTRIBUTES = *mut u8;
  21     type BOOL = i32;
  22     type LPCSTR = *const u8;
  23     type HANDLE = *mut u8;
  24     type DWORD = u32;
  25
  26     const INFINITE: DWORD = !0;
  27     const WAIT_OBJECT_0: DWORD = 0;
  28     const WAIT_ABANDONED: DWORD = 0x00000080;
  29
  30     extern "system" {
  31         fn CreateMutexA(lpMutexAttributes: LPSECURITY_ATTRIBUTES,
  32                         bInitialOwner: BOOL,
  33                         lpName: LPCSTR)
  34                         -> HANDLE;
  35         fn WaitForSingleObject(hHandle: HANDLE, dwMilliseconds: DWORD) -> DWORD;
  36         fn ReleaseMutex(hMutex: HANDLE) -> BOOL;
  37         fn CloseHandle(hObject: HANDLE) -> BOOL;
  38     }
  39
  40     struct Handle(HANDLE);
  41
  42     impl Drop for Handle {
  43         fn drop(&mut self) {
  44             unsafe {
  45                 CloseHandle(self.0);
  46             }
  47         }
  48     }
  49
  50     struct Guard(Handle);
  51
  52     impl Drop for Guard {
  53         fn drop(&mut self) {
  54             unsafe {
  55                 ReleaseMutex((self.0).0);
  56             }
  57         }
  58     }
  59
  60     let cname = CString::new(name).unwrap();
  61     unsafe {
  62         // Create a named mutex, with no security attributes and also not
  63         // acquired when we create it.
  64         //
  65         // This will silently create one if it doesn't already exist, or it'll
  66         // open up a handle to one if it already exists.
  67         let mutex = CreateMutexA(0 as *mut _, 0, cname.as_ptr() as *const u8);
  68         if mutex.is_null() {
  69             panic!("failed to create global mutex named `{}`: {}",
  70                    name,
  71                    io::Error::last_os_error());
  72         }
  73         let mutex = Handle(mutex);
  74
  75         // Acquire the lock through `WaitForSingleObject`.
  76         //
  77         // A return value of `WAIT_OBJECT_0` means we successfully acquired it.
  78         //
  79         // A return value of `WAIT_ABANDONED` means that the previous holder of
  80         // the thread exited without calling `ReleaseMutex`. This can happen,
  81         // for example, when the compiler crashes or is interrupted via ctrl-c
  82         // or the like. In this case, however, we are still transferred
  83         // ownership of the lock so we continue.
  84         //
  85         // If an error happens.. well... that's surprising!
  86         match WaitForSingleObject(mutex.0, INFINITE) {
  87             WAIT_OBJECT_0 | WAIT_ABANDONED => {}
  88             code => {
  89                 panic!("WaitForSingleObject failed on global mutex named \
  90                         `{}`: {} (ret={:x})",
  91                        name,
  92                        io::Error::last_os_error(),
  93                        code);
  94             }
  95         }
  96
  97         // Return a guard which will call `ReleaseMutex` when dropped.
  98         Box::new(Guard(mutex))
  99     }
 100 }
 101
 102 #[cfg(not(windows))]
 103 pub fn acquire_global_lock(_name: &str) -> Box<dyn Any> {
 104     Box::new(())
 105 }