// Copyright 2012 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.

#[doc(hidden)];

use libc::c_void;
use ptr::null;
use unstable::intrinsics::TyDesc;
use unstable::raw;

type DropGlue<'self> = &'self fn(**TyDesc, *c_void);

/*
 * Box annihilation
 *
 * This runs at task death to free all boxes.
 */

struct AnnihilateStats {
    n_total_boxes: uint,
    n_unique_boxes: uint,
    n_bytes_freed: uint
}

unsafe fn each_live_alloc(read_next_before: bool,
                          f: &fn(box: *mut raw::Box<()>, uniq: bool) -> bool) -> bool {
    //! Walks the internal list of allocations

    use managed;
    use rt::local_heap;

    let mut box = local_heap::live_allocs();
    while box != null() {
        let next_before = (*box).next;
        let uniq = (*box).ref_count == managed::RC_MANAGED_UNIQUE;

        if !f(box as *mut raw::Box<()>, uniq) {
            return false;
        }

        if read_next_before {
            box = next_before;
        } else {
            box = (*box).next;
        }
    }
    return true;
}

#[cfg(unix)]
fn debug_mem() -> bool {
    // XXX: Need to port the environment struct to newsched
    false
}

#[cfg(windows)]
fn debug_mem() -> bool {
    false
}

/// Destroys all managed memory (i.e. @ boxes) held by the current task.
pub unsafe fn annihilate() {
    use rt::local_heap::local_free;
    use sys;
    use managed;

    let mut stats = AnnihilateStats {
        n_total_boxes: 0,
        n_unique_boxes: 0,
        n_bytes_freed: 0
    };

    // Pass 1: Make all boxes immortal.
    //
    // In this pass, nothing gets freed, so it does not matter whether
    // we read the next field before or after the callback.
    do each_live_alloc(true) |box, uniq| {
        stats.n_total_boxes += 1;
        if uniq {
            stats.n_unique_boxes += 1;
        } else {
            (*box).ref_count = managed::RC_IMMORTAL;
        }
        true
    };

    // Pass 2: Drop all boxes.
    //
    // In this pass, unique-managed boxes may get freed, but not
    // managed boxes, so we must read the `next` field *after* the
    // callback, as the original value may have been freed.
    do each_live_alloc(false) |box, uniq| {
        if !uniq {
            let tydesc = (*box).type_desc;
            let data = &(*box).data as *();
            ((*tydesc).drop_glue)(data as *i8);
        }
        true
    };

    // Pass 3: Free all boxes.
    //
    // In this pass, managed boxes may get freed (but not
    // unique-managed boxes, though I think that none of those are
    // left), so we must read the `next` field before, since it will
    // not be valid after.
    do each_live_alloc(true) |box, uniq| {
        if !uniq {
            stats.n_bytes_freed +=
                (*((*box).type_desc)).size
                + sys::size_of::<raw::Box<()>>();
            local_free(box as *i8);
        }
        true
    };

    if debug_mem() {
        // We do logging here w/o allocation.
        debug2!("annihilator stats:\n  \
                       total boxes: {}\n  \
                      unique boxes: {}\n  \
                       bytes freed: {}",
                stats.n_total_boxes, stats.n_unique_boxes, stats.n_bytes_freed);
    }
}