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//! 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(())
}
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