1 files changed, 303 insertions, 0 deletions
diff --git a/library/std/src/sys/unix/futex.rs b/library/std/src/sys/unix/futex.rs
new file mode 100644
index 000000000..8d5b54021
--- /dev/null
+++ b/library/std/src/sys/unix/futex.rs
@@ -0,0 +1,303 @@
+#![cfg(any(
+    target_os = "linux",
+    target_os = "android",
+    all(target_os = "emscripten", target_feature = "atomics"),
+    target_os = "freebsd",
+    target_os = "openbsd",
+    target_os = "dragonfly",
+    target_os = "fuchsia",
+))]
+
+use crate::sync::atomic::AtomicU32;
+use crate::time::Duration;
+
+/// Wait for a futex_wake operation to wake us.
+///
+/// Returns directly if the futex doesn't hold the expected value.
+///
+/// Returns false on timeout, and true in all other cases.
+#[cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd"))]
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    use super::time::Timespec;
+    use crate::ptr::null;
+    use crate::sync::atomic::Ordering::Relaxed;
+
+    // Calculate the timeout as an absolute timespec.
+    //
+    // Overflows are rounded up to an infinite timeout (None).
+    let timespec = timeout
+        .and_then(|d| Timespec::now(libc::CLOCK_MONOTONIC).checked_add_duration(&d))
+        .and_then(|t| t.to_timespec());
+
+    loop {
+        // No need to wait if the value already changed.
+        if futex.load(Relaxed) != expected {
+            return true;
+        }
+
+        let r = unsafe {
+            cfg_if::cfg_if! {
+                if #[cfg(target_os = "freebsd")] {
+                    // FreeBSD doesn't have futex(), but it has
+                    // _umtx_op(UMTX_OP_WAIT_UINT_PRIVATE), which is nearly
+                    // identical. It supports absolute timeouts through a flag
+                    // in the _umtx_time struct.
+                    let umtx_timeout = timespec.map(|t| libc::_umtx_time {
+                        _timeout: t,
+                        _flags: libc::UMTX_ABSTIME,
+                        _clockid: libc::CLOCK_MONOTONIC as u32,
+                    });
+                    let umtx_timeout_ptr = umtx_timeout.as_ref().map_or(null(), |t| t as *const _);
+                    let umtx_timeout_size = umtx_timeout.as_ref().map_or(0, |t| crate::mem::size_of_val(t));
+                    libc::_umtx_op(
+                        futex as *const AtomicU32 as *mut _,
+                        libc::UMTX_OP_WAIT_UINT_PRIVATE,
+                        expected as libc::c_ulong,
+                        crate::ptr::invalid_mut(umtx_timeout_size),
+                        umtx_timeout_ptr as *mut _,
+                    )
+                } else if #[cfg(any(target_os = "linux", target_os = "android"))] {
+                    // Use FUTEX_WAIT_BITSET rather than FUTEX_WAIT to be able to give an
+                    // absolute time rather than a relative time.
+                    libc::syscall(
+                        libc::SYS_futex,
+                        futex as *const AtomicU32,
+                        libc::FUTEX_WAIT_BITSET | libc::FUTEX_PRIVATE_FLAG,
+                        expected,
+                        timespec.as_ref().map_or(null(), |t| t as *const libc::timespec),
+                        null::<u32>(), // This argument is unused for FUTEX_WAIT_BITSET.
+                        !0u32,         // A full bitmask, to make it behave like a regular FUTEX_WAIT.
+                    )
+                } else {
+                    compile_error!("unknown target_os");
+                }
+            }
+        };
+
+        match (r < 0).then(super::os::errno) {
+            Some(libc::ETIMEDOUT) => return false,
+            Some(libc::EINTR) => continue,
+            _ => return true,
+        }
+    }
+}
+
+/// Wake up one thread that's blocked on futex_wait on this futex.
+///
+/// Returns true if this actually woke up such a thread,
+/// or false if no thread was waiting on this futex.
+///
+/// On some platforms, this always returns false.
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    let ptr = futex as *const AtomicU32;
+    let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
+    unsafe { libc::syscall(libc::SYS_futex, ptr, op, 1) > 0 }
+}
+
+/// Wake up all threads that are waiting on futex_wait on this futex.
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    let ptr = futex as *const AtomicU32;
+    let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
+    unsafe {
+        libc::syscall(libc::SYS_futex, ptr, op, i32::MAX);
+    }
+}
+
+// FreeBSD doesn't tell us how many threads are woken up, so this always returns false.
+#[cfg(target_os = "freebsd")]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    use crate::ptr::null_mut;
+    unsafe {
+        libc::_umtx_op(
+            futex as *const AtomicU32 as *mut _,
+            libc::UMTX_OP_WAKE_PRIVATE,
+            1,
+            null_mut(),
+            null_mut(),
+        )
+    };
+    false
+}
+
+#[cfg(target_os = "freebsd")]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    use crate::ptr::null_mut;
+    unsafe {
+        libc::_umtx_op(
+            futex as *const AtomicU32 as *mut _,
+            libc::UMTX_OP_WAKE_PRIVATE,
+            i32::MAX as libc::c_ulong,
+            null_mut(),
+            null_mut(),
+        )
+    };
+}
+
+#[cfg(target_os = "openbsd")]
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    use super::time::Timespec;
+    use crate::ptr::{null, null_mut};
+
+    // Overflows are rounded up to an infinite timeout (None).
+    let timespec = timeout
+        .and_then(|d| Timespec::zero().checked_add_duration(&d))
+        .and_then(|t| t.to_timespec());
+
+    let r = unsafe {
+        libc::futex(
+            futex as *const AtomicU32 as *mut u32,
+            libc::FUTEX_WAIT,
+            expected as i32,
+            timespec.as_ref().map_or(null(), |t| t as *const libc::timespec),
+            null_mut(),
+        )
+    };
+
+    r == 0 || super::os::errno() != libc::ETIMEDOUT
+}
+
+#[cfg(target_os = "openbsd")]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    use crate::ptr::{null, null_mut};
+    unsafe {
+        libc::futex(futex as *const AtomicU32 as *mut u32, libc::FUTEX_WAKE, 1, null(), null_mut())
+            > 0
+    }
+}
+
+#[cfg(target_os = "openbsd")]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    use crate::ptr::{null, null_mut};
+    unsafe {
+        libc::futex(
+            futex as *const AtomicU32 as *mut u32,
+            libc::FUTEX_WAKE,
+            i32::MAX,
+            null(),
+            null_mut(),
+        );
+    }
+}
+
+#[cfg(target_os = "dragonfly")]
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    // A timeout of 0 means infinite.
+    // We round smaller timeouts up to 1 millisecond.
+    // Overflows are rounded up to an infinite timeout.
+    let timeout_ms =
+        timeout.and_then(|d| Some(i32::try_from(d.as_millis()).ok()?.max(1))).unwrap_or(0);
+
+    let r = unsafe {
+        libc::umtx_sleep(futex as *const AtomicU32 as *const i32, expected as i32, timeout_ms)
+    };
+
+    r == 0 || super::os::errno() != libc::ETIMEDOUT
+}
+
+// DragonflyBSD doesn't tell us how many threads are woken up, so this always returns false.
+#[cfg(target_os = "dragonfly")]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, 1) };
+    false
+}
+
+#[cfg(target_os = "dragonfly")]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, i32::MAX) };
+}
+
+#[cfg(target_os = "emscripten")]
+extern "C" {
+    fn emscripten_futex_wake(addr: *const AtomicU32, count: libc::c_int) -> libc::c_int;
+    fn emscripten_futex_wait(
+        addr: *const AtomicU32,
+        val: libc::c_uint,
+        max_wait_ms: libc::c_double,
+    ) -> libc::c_int;
+}
+
+#[cfg(target_os = "emscripten")]
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    unsafe {
+        emscripten_futex_wait(
+            futex,
+            expected,
+            timeout.map_or(f64::INFINITY, |d| d.as_secs_f64() * 1000.0),
+        ) != -libc::ETIMEDOUT
+    }
+}
+
+#[cfg(target_os = "emscripten")]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    unsafe { emscripten_futex_wake(futex, 1) > 0 }
+}
+
+#[cfg(target_os = "emscripten")]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    unsafe { emscripten_futex_wake(futex, i32::MAX) };
+}
+
+#[cfg(target_os = "fuchsia")]
+pub mod zircon {
+    pub type zx_futex_t = crate::sync::atomic::AtomicU32;
+    pub type zx_handle_t = u32;
+    pub type zx_status_t = i32;
+    pub type zx_time_t = i64;
+
+    pub const ZX_HANDLE_INVALID: zx_handle_t = 0;
+
+    pub const ZX_TIME_INFINITE: zx_time_t = zx_time_t::MAX;
+
+    pub const ZX_OK: zx_status_t = 0;
+    pub const ZX_ERR_INVALID_ARGS: zx_status_t = -10;
+    pub const ZX_ERR_BAD_HANDLE: zx_status_t = -11;
+    pub const ZX_ERR_WRONG_TYPE: zx_status_t = -12;
+    pub const ZX_ERR_BAD_STATE: zx_status_t = -20;
+    pub const ZX_ERR_TIMED_OUT: zx_status_t = -21;
+
+    extern "C" {
+        pub fn zx_clock_get_monotonic() -> zx_time_t;
+        pub fn zx_futex_wait(
+            value_ptr: *const zx_futex_t,
+            current_value: zx_futex_t,
+            new_futex_owner: zx_handle_t,
+            deadline: zx_time_t,
+        ) -> zx_status_t;
+        pub fn zx_futex_wake(value_ptr: *const zx_futex_t, wake_count: u32) -> zx_status_t;
+        pub fn zx_futex_wake_single_owner(value_ptr: *const zx_futex_t) -> zx_status_t;
+        pub fn zx_thread_self() -> zx_handle_t;
+    }
+}
+
+#[cfg(target_os = "fuchsia")]
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    use crate::convert::TryFrom;
+
+    // Sleep forever if the timeout is longer than fits in a i64.
+    let deadline = timeout
+        .and_then(|d| {
+            i64::try_from(d.as_nanos())
+                .ok()?
+                .checked_add(unsafe { zircon::zx_clock_get_monotonic() })
+        })
+        .unwrap_or(zircon::ZX_TIME_INFINITE);
+
+    unsafe {
+        zircon::zx_futex_wait(futex, AtomicU32::new(expected), zircon::ZX_HANDLE_INVALID, deadline)
+            != zircon::ZX_ERR_TIMED_OUT
+    }
+}
+
+// Fuchsia doesn't tell us how many threads are woken up, so this always returns false.
+#[cfg(target_os = "fuchsia")]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    unsafe { zircon::zx_futex_wake(futex, 1) };
+    false
+}
+
+#[cfg(target_os = "fuchsia")]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    unsafe { zircon::zx_futex_wake(futex, u32::MAX) };
+}