Add SGX thread parker

core/src/lib.rs

@@ -39,17 +39,29 @@
 
 #![warn(missing_docs)]
 #![warn(rust_2018_idioms)]
+#![cfg_attr(feature = "nightly", feature(sgx_platform))]
 
 #[cfg(all(feature = "nightly", target_os = "linux"))]
 #[path = "thread_parker/linux.rs"]
 mod thread_parker;
+
 #[cfg(all(unix, not(all(feature = "nightly", target_os = "linux"))))]
 #[path = "thread_parker/unix.rs"]
 mod thread_parker;
+
 #[cfg(windows)]
 #[path = "thread_parker/windows/mod.rs"]
 mod thread_parker;
-#[cfg(not(any(windows, unix)))]
+
+#[cfg(all(feature = "nightly", target_vendor = "fortanix", target_env = "sgx"))]
+#[path = "thread_parker/sgx.rs"]
+mod thread_parker;
+
+#[cfg(not(any(
+    windows,
+    unix,
+    all(feature = "nightly", target_vendor = "fortanix", target_env = "sgx")
+)))]
 #[path = "thread_parker/generic.rs"]
 mod thread_parker;
 

core/src/thread_parker/sgx.rs

@@ -0,0 +1,105 @@
+// Copyright 2016 Amanieu d'Antras
+//
+// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
+// http://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.
+
+use core::sync::atomic::{spin_loop_hint, AtomicBool, Ordering};
+use std::{
+    os::fortanix_sgx::{
+        thread::current as current_tcs,
+        usercalls::{
+            self,
+            raw::{Tcs, EV_UNPARK, WAIT_INDEFINITE},
+        },
+    },
+    thread,
+    time::Instant,
+};
+
+// Helper type for putting a thread to sleep until some other thread wakes it up
+pub struct ThreadParker {
+    parked: AtomicBool,
+    tcs: Tcs,
+}
+
+impl ThreadParker {
+    pub const IS_CHEAP_TO_CONSTRUCT: bool = true;
+
+    #[inline]
+    pub fn new() -> ThreadParker {
+        ThreadParker {
+            parked: AtomicBool::new(false),
+            tcs: current_tcs(),
+        }
+    }
+
+    // Prepares the parker. This should be called before adding it to the queue.
+    #[inline]
+    pub fn prepare_park(&self) {
+        self.parked.store(true, Ordering::Relaxed);
+    }
+
+    // Checks if the park timed out. This should be called while holding the
+    // queue lock after park_until has returned false.
+    #[inline]
+    pub fn timed_out(&self) -> bool {
+        self.parked.load(Ordering::Relaxed)
+    }
+
+    // Parks the thread until it is unparked. This should be called after it has
+    // been added to the queue, after unlocking the queue.
+    #[inline]
+    pub fn park(&self) {
+        while self.parked.load(Ordering::Acquire) {
+            let res = usercalls::wait(EV_UNPARK, WAIT_INDEFINITE).expect("wait returned error");
+            assert_eq!(res & EV_UNPARK, EV_UNPARK);
+        }
+    }
+
+    // Parks the thread until it is unparked or the timeout is reached. This
+    // should be called after it has been added to the queue, after unlocking
+    // the queue. Returns true if we were unparked and false if we timed out.
+    #[inline]
+    pub fn park_until(&self, timeout: Instant) -> bool {
+        while self.parked.load(Ordering::Acquire) {
+            if Instant::now() >= timeout {
+                return false;
+            }
+            // SGX current does not support waiting for an event with a
+            // timeout. So we just implement this as a busy spin loop.
+            spin_loop_hint();
+        }
+        true
+    }
+
+    // Locks the parker to prevent the target thread from exiting. This is
+    // necessary to ensure that thread-local ThreadData objects remain valid.
+    // This should be called while holding the queue lock.
+    #[inline]
+    pub fn unpark_lock(&self) -> UnparkHandle {
+        // We don't need to lock anything, just clear the state
+        self.parked.store(false, Ordering::Release);
+        UnparkHandle(self.tcs)
+    }
+}
+
+// Handle for a thread that is about to be unparked. We need to mark the thread
+// as unparked while holding the queue lock, but we delay the actual unparking
+// until after the queue lock is released.
+pub struct UnparkHandle(Tcs);
+
+impl UnparkHandle {
+    // Wakes up the parked thread. This should be called after the queue lock is
+    // released to avoid blocking the queue for too long.
+    #[inline]
+    pub fn unpark(self) {
+        usercalls::send(EV_UNPARK, Some(self.0)).expect("send returned error");
+    }
+}
+
+#[inline]
+pub fn thread_yield() {
+    thread::yield_now();
+}