rust/src/libstd/local_data.rs

// Copyright 2012-2013 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.

/*!

Task local data management

Allows storing boxes with arbitrary types inside, to be accessed anywhere within
a task, keyed by a pointer to a global finaliser function. Useful for dynamic
variables, singletons, and interfacing with foreign code with bad callback
interfaces.

To use, declare a monomorphic (no type parameters) global function at the type
to store, and use it as the 'key' when accessing.

~~~{.rust}
use std::local_data;

fn key_int(_: @int) {}
fn key_vector(_: @~[int]) {}

unsafe {
    local_data::set(key_int, @3);
    assert!(local_data::get(key_int) == Some(@3));

    local_data::set(key_vector, @~[3]);
    assert!(local_data::get(key_vector).unwrap()[0] == 3);
}
~~~

Casting 'Arcane Sight' reveals an overwhelming aura of Transmutation
magic.

*/

use prelude::*;

use task::local_data_priv::{local_get, local_pop, local_set, Handle};

#[cfg(test)] use task;

/**
 * Indexes a task-local data slot. The function's code pointer is used for
 * comparison. Recommended use is to write an empty function for each desired
 * task-local data slot (and use class destructors, not code inside the
 * function, if specific teardown is needed). DO NOT use multiple
 * instantiations of a single polymorphic function to index data of different
 * types; arbitrary type coercion is possible this way.
 *
 * One other exception is that this global state can be used in a destructor
 * context to create a circular @-box reference, which will crash during task
 * failure (see issue #3039).
 *
 * These two cases aside, the interface is safe.
 */
pub type Key<'self,T> = &'self fn:Copy(v: T);

/**
 * Remove a task-local data value from the table, returning the
 * reference that was originally created to insert it.
 */
#[cfg(stage0)]
pub unsafe fn pop<T: 'static>(key: Key<@T>) -> Option<@T> {
    local_pop(Handle::new(), key)
}
/**
 * Remove a task-local data value from the table, returning the
 * reference that was originally created to insert it.
 */
#[cfg(not(stage0))]
pub unsafe fn pop<T: 'static>(key: Key<T>) -> Option<T> {
    local_pop(Handle::new(), key)
}
/**
 * Retrieve a task-local data value. It will also be kept alive in the
 * table until explicitly removed.
 */
#[cfg(stage0)]
pub unsafe fn get<T: 'static>(key: Key<@T>) -> Option<@T> {
    local_get(Handle::new(), key, |loc| loc.map(|&x| *x))
}
/**
 * Retrieve a task-local data value. It will also be kept alive in the
 * table until explicitly removed.
 */
#[cfg(not(stage0))]
pub unsafe fn get<T: 'static>(key: Key<@T>) -> Option<@T> {
    local_get(Handle::new(), key, |loc| loc.map(|&x| *x))
}
/**
 * Store a value in task-local data. If this key already has a value,
 * that value is overwritten (and its destructor is run).
 */
#[cfg(stage0)]
pub unsafe fn set<T: 'static>(key: Key<@T>, data: @T) {
    local_set(Handle::new(), key, data)
}
/**
 * Store a value in task-local data. If this key already has a value,
 * that value is overwritten (and its destructor is run).
 */
#[cfg(not(stage0))]
pub unsafe fn set<T: 'static>(key: Key<T>, data: T) {
    local_set(Handle::new(), key, data)
}
/**
 * Modify a task-local data value. If the function returns 'None', the
 * data is removed (and its reference dropped).
 */
#[cfg(stage0)]
pub unsafe fn modify<T: 'static>(key: Key<@T>,
                                 f: &fn(Option<@T>) -> Option<@T>) {
    match f(pop(key)) {
        Some(next) => { set(key, next); }
        None => {}
    }
}
/**
 * Modify a task-local data value. If the function returns 'None', the
 * data is removed (and its reference dropped).
 */
#[cfg(not(stage0))]
pub unsafe fn modify<T: 'static>(key: Key<T>,
                                 f: &fn(Option<T>) -> Option<T>) {
    match f(pop(key)) {
        Some(next) => { set(key, next); }
        None => {}
    }
}

#[test]
fn test_tls_multitask() {
    unsafe {
        fn my_key(_x: @~str) { }
        set(my_key, @~"parent data");
        do task::spawn {
            // TLS shouldn't carry over.
            assert!(get(my_key).is_none());
            set(my_key, @~"child data");
            assert!(*(get(my_key).get()) ==
                    ~"child data");
            // should be cleaned up for us
        }
        // Must work multiple times
        assert!(*(get(my_key).get()) == ~"parent data");
        assert!(*(get(my_key).get()) == ~"parent data");
        assert!(*(get(my_key).get()) == ~"parent data");
    }
}

#[test]
fn test_tls_overwrite() {
    unsafe {
        fn my_key(_x: @~str) { }
        set(my_key, @~"first data");
        set(my_key, @~"next data"); // Shouldn't leak.
        assert!(*(get(my_key).get()) == ~"next data");
    }
}

#[test]
fn test_tls_pop() {
    unsafe {
        fn my_key(_x: @~str) { }
        set(my_key, @~"weasel");
        assert!(*(pop(my_key).get()) == ~"weasel");
        // Pop must remove the data from the map.
        assert!(pop(my_key).is_none());
    }
}

#[test]
fn test_tls_modify() {
    unsafe {
        fn my_key(_x: @~str) { }
        modify(my_key, |data| {
            match data {
                Some(@ref val) => fail!("unwelcome value: %s", *val),
                None           => Some(@~"first data")
            }
        });
        modify(my_key, |data| {
            match data {
                Some(@~"first data") => Some(@~"next data"),
                Some(@ref val)       => fail!("wrong value: %s", *val),
                None                 => fail!("missing value")
            }
        });
        assert!(*(pop(my_key).get()) == ~"next data");
    }
}

#[test]
fn test_tls_crust_automorestack_memorial_bug() {
    // This might result in a stack-canary clobber if the runtime fails to
    // set sp_limit to 0 when calling the cleanup extern - it might
    // automatically jump over to the rust stack, which causes next_c_sp
    // to get recorded as something within a rust stack segment. Then a
    // subsequent upcall (esp. for logging, think vsnprintf) would run on
    // a stack smaller than 1 MB.
    fn my_key(_x: @~str) { }
    do task::spawn {
        unsafe { set(my_key, @~"hax"); }
    }
}

#[test]
fn test_tls_multiple_types() {
    fn str_key(_x: @~str) { }
    fn box_key(_x: @@()) { }
    fn int_key(_x: @int) { }
    do task::spawn {
        unsafe {
            set(str_key, @~"string data");
            set(box_key, @@());
            set(int_key, @42);
        }
    }
}

#[test]
fn test_tls_overwrite_multiple_types() {
    fn str_key(_x: @~str) { }
    fn box_key(_x: @@()) { }
    fn int_key(_x: @int) { }
    do task::spawn {
        unsafe {
            set(str_key, @~"string data");
            set(int_key, @42);
            // This could cause a segfault if overwriting-destruction is done
            // with the crazy polymorphic transmute rather than the provided
            // finaliser.
            set(int_key, @31337);
        }
    }
}

#[test]
#[should_fail]
#[ignore(cfg(windows))]
fn test_tls_cleanup_on_failure() {
    unsafe {
        fn str_key(_x: @~str) { }
        fn box_key(_x: @@()) { }
        fn int_key(_x: @int) { }
        set(str_key, @~"parent data");
        set(box_key, @@());
        do task::spawn {
            // spawn_linked
            set(str_key, @~"string data");
            set(box_key, @@());
            set(int_key, @42);
            fail!();
        }
        // Not quite nondeterministic.
        set(int_key, @31337);
        fail!();
    }
}

#[test]
fn test_static_pointer() {
    unsafe {
        fn key(_x: @&'static int) { }
        static VALUE: int = 0;
        set(key, @&VALUE);
    }
}

#[test]
fn test_owned() {
    unsafe {
        fn key(_x: ~int) { }
        set(key, ~1);
    }
}