global.rs

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.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.

/*!
Global data

An interface for creating and retrieving values with global
(per-runtime) scope.

Global values are stored in a map and protected by a single global
mutex. Operations are provided for accessing and cloning the value
under the mutex.

Because all globals go through a single mutex, they should be used
sparingly.  The interface is intended to be used with clonable,
atomically reference counted synchronization types, like ARCs, in
which case the value should be cached locally whenever possible to
avoid hitting the mutex.
*/

use cast::{transmute};
use clone::Clone;
use kinds::Owned;
use libc::{c_void};
use option::{Option, Some, None};
use ops::Drop;
use unstable::sync::{Exclusive, exclusive};
use unstable::at_exit::at_exit;
use unstable::intrinsics::atomic_cxchg;
use hashmap::HashMap;
use sys::Closure;

#[cfg(test)] use unstable::sync::{UnsafeAtomicRcBox};
#[cfg(test)] use task::spawn;
#[cfg(test)] use uint;

pub type GlobalDataKey<'self,T> = &'self fn(v: T);

pub unsafe fn global_data_clone_create<T:Owned + Clone>(
    key: GlobalDataKey<T>, create: &fn() -> ~T) -> T {
    /*!
     * Clone a global value or, if it has not been created,
     * first construct the value then return a clone.
     *
     * # Safety note
     *
     * Both the clone operation and the constructor are
     * called while the global lock is held. Recursive
     * use of the global interface in either of these
     * operations will result in deadlock.
     */
    global_data_clone_create_(key_ptr(key), create)
}

unsafe fn global_data_clone_create_<T:Owned + Clone>(
    key: uint, create: &fn() -> ~T) -> T {

    let mut clone_value: Option<T> = None;
    do global_data_modify_(key) |value: Option<~T>| {
        match value {
            None => {
                let value = create();
                clone_value = Some((*value).clone());
                Some(value)
            }
            Some(value) => {
                clone_value = Some((*value).clone());
                Some(value)
            }
        }
    }
    return clone_value.unwrap();
}

unsafe fn global_data_modify<T:Owned>(
    key: GlobalDataKey<T>, op: &fn(Option<~T>) -> Option<~T>) {

    global_data_modify_(key_ptr(key), op)
}

unsafe fn global_data_modify_<T:Owned>(
    key: uint, op: &fn(Option<~T>) -> Option<~T>) {

    let mut old_dtor = None;
    do get_global_state().with |gs| {
        let (maybe_new_value, maybe_dtor) = match gs.map.pop(&key) {
            Some((ptr, dtor)) => {
                let value: ~T = transmute(ptr);
                (op(Some(value)), Some(dtor))
            }
            None => {
                (op(None), None)
            }
        };
        match maybe_new_value {
            Some(value) => {
                let data: *c_void = transmute(value);
                let dtor: ~fn() = match maybe_dtor {
                    Some(dtor) => dtor,
                    None => {
                        let dtor: ~fn() = || {
                            let _destroy_value: ~T = transmute(data);
                        };
                        dtor
                    }
                };
                let value = (data, dtor);
                gs.map.insert(key, value);
            }
            None => {
                match maybe_dtor {
                    Some(dtor) => old_dtor = Some(dtor),
                    None => ()
                }
            }
        }
    }
}

pub unsafe fn global_data_clone<T:Owned + Clone>(
    key: GlobalDataKey<T>) -> Option<T> {
    let mut maybe_clone: Option<T> = None;
    do global_data_modify(key) |current| {
        match &current {
            &Some(~ref value) => {
                maybe_clone = Some(value.clone());
            }
            &None => ()
        }
        current
    }
    return maybe_clone;
}

// GlobalState is a map from keys to unique pointers and a
// destructor. Keys are pointers derived from the type of the
// global value.  There is a single GlobalState instance per runtime.
struct GlobalState {
    map: HashMap<uint, (*c_void, ~fn())>
}

impl Drop for GlobalState {
    fn finalize(&self) {
        for self.map.each_value |v| {
            match v {
                &(_, ref dtor) => (*dtor)()
            }
        }
    }
}

fn get_global_state() -> Exclusive<GlobalState> {

    static POISON: int = -1;

    // FIXME #4728: Doing atomic_cxchg to initialize the global state
    // lazily, which wouldn't be necessary with a runtime written
    // in Rust
    let global_ptr = unsafe { rust_get_global_data_ptr() };

    if unsafe { *global_ptr } == 0 {
        // Global state doesn't exist yet, probably

        // The global state object
        let state = GlobalState {
            map: HashMap::new()
        };

        // It's under a reference-counted mutex
        let state = ~exclusive(state);

        // Convert it to an integer
        let state_i: int = unsafe {
            let state_ptr: &Exclusive<GlobalState> = state;
            transmute(state_ptr)
        };

        // Swap our structure into the global pointer
        let prev_i = unsafe { atomic_cxchg(&mut *global_ptr, 0, state_i) };

        // Sanity check that we're not trying to reinitialize after shutdown
        assert!(prev_i != POISON);

        if prev_i == 0 {
            // Successfully installed the global pointer

            // Take a handle to return
            let clone = (*state).clone();

            // Install a runtime exit function to destroy the global object
            do at_exit {
                // Poison the global pointer
                let prev_i = unsafe {
                    atomic_cxchg(&mut *global_ptr, state_i, POISON)
                };
                assert_eq!(prev_i, state_i);

                // Capture the global state object in the at_exit closure
                // so that it is destroyed at the right time
                let _capture_global_state = &state;
            };
            return clone;
        } else {
            // Somebody else initialized the globals first
            let state: &Exclusive<GlobalState> = unsafe { transmute(prev_i) };
            return state.clone();
        }
    } else {
        let state: &Exclusive<GlobalState> = unsafe {
            transmute(*global_ptr)
        };
        return state.clone();
    }
}

fn key_ptr<T:Owned>(key: GlobalDataKey<T>) -> uint {
    unsafe {
        let closure: Closure = transmute(key);
        return transmute(closure.code);
    }
}

extern {
    fn rust_get_global_data_ptr() -> *mut int;
}

#[test]
fn test_clone_rc() {
    fn key(_v: UnsafeAtomicRcBox<int>) { }

    for uint::range(0, 100) |_| {
        do spawn {
            unsafe {
                let val = do global_data_clone_create(key) {
                    ~UnsafeAtomicRcBox::new(10)
                };

                assert!(val.get() == &10);
            }
        }
    }
}

#[test]
fn test_modify() {
    fn key(_v: UnsafeAtomicRcBox<int>) { }

    unsafe {
        do global_data_modify(key) |v| {
            match v {
                None => { Some(~UnsafeAtomicRcBox::new(10)) }
                _ => fail!()
            }
        }

        do global_data_modify(key) |v| {
            match v {
                Some(sms) => {
                    let v = sms.get();
                    assert!(*v == 10);
                    None
                },
                _ => fail!()
            }
        }

        do global_data_modify(key) |v| {
            match v {
                None => { Some(~UnsafeAtomicRcBox::new(10)) }
                _ => fail!()
            }
        }
    }
}