1 files changed, 266 insertions, 0 deletions
diff --git a/third_party/rust/jobserver/src/windows.rs b/third_party/rust/jobserver/src/windows.rs
new file mode 100644
index 0000000000..6791efea4f
--- /dev/null
+++ b/third_party/rust/jobserver/src/windows.rs
@@ -0,0 +1,266 @@
+use std::ffi::CString;
+use std::io;
+use std::process::Command;
+use std::ptr;
+use std::sync::Arc;
+use std::thread::{Builder, JoinHandle};
+
+#[derive(Debug)]
+pub struct Client {
+    sem: Handle,
+    name: String,
+}
+
+#[derive(Debug)]
+pub struct Acquired;
+
+type BOOL = i32;
+type DWORD = u32;
+type HANDLE = *mut u8;
+type LONG = i32;
+
+const ERROR_ALREADY_EXISTS: DWORD = 183;
+const FALSE: BOOL = 0;
+const INFINITE: DWORD = 0xffffffff;
+const SEMAPHORE_MODIFY_STATE: DWORD = 0x2;
+const SYNCHRONIZE: DWORD = 0x00100000;
+const TRUE: BOOL = 1;
+const WAIT_OBJECT_0: DWORD = 0;
+
+extern "system" {
+    fn CloseHandle(handle: HANDLE) -> BOOL;
+    fn SetEvent(hEvent: HANDLE) -> BOOL;
+    fn WaitForMultipleObjects(
+        ncount: DWORD,
+        lpHandles: *const HANDLE,
+        bWaitAll: BOOL,
+        dwMilliseconds: DWORD,
+    ) -> DWORD;
+    fn CreateEventA(
+        lpEventAttributes: *mut u8,
+        bManualReset: BOOL,
+        bInitialState: BOOL,
+        lpName: *const i8,
+    ) -> HANDLE;
+    fn ReleaseSemaphore(
+        hSemaphore: HANDLE,
+        lReleaseCount: LONG,
+        lpPreviousCount: *mut LONG,
+    ) -> BOOL;
+    fn CreateSemaphoreA(
+        lpEventAttributes: *mut u8,
+        lInitialCount: LONG,
+        lMaximumCount: LONG,
+        lpName: *const i8,
+    ) -> HANDLE;
+    fn OpenSemaphoreA(dwDesiredAccess: DWORD, bInheritHandle: BOOL, lpName: *const i8) -> HANDLE;
+    fn WaitForSingleObject(hHandle: HANDLE, dwMilliseconds: DWORD) -> DWORD;
+    #[link_name = "SystemFunction036"]
+    fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: u32) -> u8;
+}
+
+// Note that we ideally would use the `getrandom` crate, but unfortunately
+// that causes build issues when this crate is used in rust-lang/rust (see
+// rust-lang/rust#65014 for more information). As a result we just inline
+// the pretty simple Windows-specific implementation of generating
+// randomness.
+fn getrandom(dest: &mut [u8]) -> io::Result<()> {
+    // Prevent overflow of u32
+    for chunk in dest.chunks_mut(u32::max_value() as usize) {
+        let ret = unsafe { RtlGenRandom(chunk.as_mut_ptr(), chunk.len() as u32) };
+        if ret == 0 {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "failed to generate random bytes",
+            ));
+        }
+    }
+    Ok(())
+}
+
+impl Client {
+    pub fn new(limit: usize) -> io::Result<Client> {
+        // Try a bunch of random semaphore names until we get a unique one,
+        // but don't try for too long.
+        //
+        // Note that `limit == 0` is a valid argument above but Windows
+        // won't let us create a semaphore with 0 slots available to it. Get
+        // `limit == 0` working by creating a semaphore instead with one
+        // slot and then immediately acquire it (without ever releaseing it
+        // back).
+        for _ in 0..100 {
+            let mut bytes = [0; 4];
+            getrandom(&mut bytes)?;
+            let mut name = format!("__rust_jobserver_semaphore_{}\0", u32::from_ne_bytes(bytes));
+            unsafe {
+                let create_limit = if limit == 0 { 1 } else { limit };
+                let r = CreateSemaphoreA(
+                    ptr::null_mut(),
+                    create_limit as LONG,
+                    create_limit as LONG,
+                    name.as_ptr() as *const _,
+                );
+                if r.is_null() {
+                    return Err(io::Error::last_os_error());
+                }
+                let handle = Handle(r);
+
+                let err = io::Error::last_os_error();
+                if err.raw_os_error() == Some(ERROR_ALREADY_EXISTS as i32) {
+                    continue;
+                }
+                name.pop(); // chop off the trailing nul
+                let client = Client {
+                    sem: handle,
+                    name: name,
+                };
+                if create_limit != limit {
+                    client.acquire()?;
+                }
+                return Ok(client);
+            }
+        }
+
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "failed to find a unique name for a semaphore",
+        ))
+    }
+
+    pub unsafe fn open(s: &str) -> Option<Client> {
+        let name = match CString::new(s) {
+            Ok(s) => s,
+            Err(_) => return None,
+        };
+
+        let sem = OpenSemaphoreA(SYNCHRONIZE | SEMAPHORE_MODIFY_STATE, FALSE, name.as_ptr());
+        if sem.is_null() {
+            None
+        } else {
+            Some(Client {
+                sem: Handle(sem),
+                name: s.to_string(),
+            })
+        }
+    }
+
+    pub fn acquire(&self) -> io::Result<Acquired> {
+        unsafe {
+            let r = WaitForSingleObject(self.sem.0, INFINITE);
+            if r == WAIT_OBJECT_0 {
+                Ok(Acquired)
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+
+    pub fn release(&self, _data: Option<&Acquired>) -> io::Result<()> {
+        unsafe {
+            let r = ReleaseSemaphore(self.sem.0, 1, ptr::null_mut());
+            if r != 0 {
+                Ok(())
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+
+    pub fn string_arg(&self) -> String {
+        self.name.clone()
+    }
+
+    pub fn available(&self) -> io::Result<usize> {
+        // Can't read value of a semaphore on Windows, so
+        // try to acquire without sleeping, since we can find out the
+        // old value on release. If acquisiton fails, then available is 0.
+        unsafe {
+            let r = WaitForSingleObject(self.sem.0, 0);
+            if r != WAIT_OBJECT_0 {
+                Ok(0)
+            } else {
+                let mut prev: LONG = 0;
+                let r = ReleaseSemaphore(self.sem.0, 1, &mut prev);
+                if r != 0 {
+                    Ok(prev as usize + 1)
+                } else {
+                    Err(io::Error::last_os_error())
+                }
+            }
+        }
+    }
+
+    pub fn configure(&self, _cmd: &mut Command) {
+        // nothing to do here, we gave the name of our semaphore to the
+        // child above
+    }
+}
+
+#[derive(Debug)]
+struct Handle(HANDLE);
+// HANDLE is a raw ptr, but we're send/sync
+unsafe impl Sync for Handle {}
+unsafe impl Send for Handle {}
+
+impl Drop for Handle {
+    fn drop(&mut self) {
+        unsafe {
+            CloseHandle(self.0);
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Helper {
+    event: Arc<Handle>,
+    thread: JoinHandle<()>,
+}
+
+pub(crate) fn spawn_helper(
+    client: crate::Client,
+    state: Arc<super::HelperState>,
+    mut f: Box<dyn FnMut(io::Result<crate::Acquired>) + Send>,
+) -> io::Result<Helper> {
+    let event = unsafe {
+        let r = CreateEventA(ptr::null_mut(), TRUE, FALSE, ptr::null());
+        if r.is_null() {
+            return Err(io::Error::last_os_error());
+        } else {
+            Handle(r)
+        }
+    };
+    let event = Arc::new(event);
+    let event2 = event.clone();
+    let thread = Builder::new().spawn(move || {
+        let objects = [event2.0, client.inner.sem.0];
+        state.for_each_request(|_| {
+            const WAIT_OBJECT_1: u32 = WAIT_OBJECT_0 + 1;
+            match unsafe { WaitForMultipleObjects(2, objects.as_ptr(), FALSE, INFINITE) } {
+                WAIT_OBJECT_0 => return,
+                WAIT_OBJECT_1 => f(Ok(crate::Acquired {
+                    client: client.inner.clone(),
+                    data: Acquired,
+                    disabled: false,
+                })),
+                _ => f(Err(io::Error::last_os_error())),
+            }
+        });
+    })?;
+    Ok(Helper { thread, event })
+}
+
+impl Helper {
+    pub fn join(self) {
+        // Unlike unix this logic is much easier. If our thread was blocked
+        // in waiting for requests it should already be woken up and
+        // exiting. Otherwise it's waiting for a token, so we wake it up
+        // with a different event that it's also waiting on here. After
+        // these two we should be guaranteed the thread is on its way out,
+        // so we can safely `join`.
+        let r = unsafe { SetEvent(self.event.0) };
+        if r == 0 {
+            panic!("failed to set event: {}", io::Error::last_os_error());
+        }
+        drop(self.thread.join());
+    }
+}