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// Copyright 2015 Pierre-Étienne Meunier and Florent Becker. See the
// COPYRIGHT file at the top-level directory of this distribution and
// at http://pijul.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.
use {Transaction, Representable, PageT, MutTxn, Db, Error, CursorStack, PAGE_SIZE_U16};
use transaction::Cow;
use skiplist::{SkipListPage, FIRST_BINDING_SIZE, record_size};
use skiplist;
use std;
use rand::Rng;
impl<'env, T> MutTxn<'env, T> {
/// Insert a binding to a database, returning `false` if and only
/// if the exact same binding (key *and* value) was already in the database.
pub fn put<R: Rng, K: Representable, V: Representable>(&mut self,
rng: &mut R,
db: &mut Db<K, V>,
key: K,
value: V)
-> Result<bool, Error> {
let mut cursor = CursorStack::new();
if cursor.set(self, db, Some((key, Some(value))))? {
return Ok(false);
}
// Now insert in the leaf and split all pages that need to be split.
let leaf_pointer = cursor.pointer;
// Split all pages that need it.
//
// This loop uses unsafe slices, but the memory management is
// simple: all pointers used in the loop are valid until we
// explicitely call free, after the loop.
let last_allocated;
{
let mut inserted_right_child = 0;
let mut inserted_key = key;
let mut inserted_value = value;
let mut inserted_left_child = 0u64;
loop {
let mut page = self.load_cow_page(cursor.current().page);
debug!("page: {:?}", page);
// If we're "CoWing" the first double-pointed page on the stack, decrease its RC.
if cursor.pointer == cursor.first_rc_level {
let page = cursor.current().page;
let rc = self.rc(page);
if rc >= 2 {
try!(self.set_rc(rng, page, rc - 1));
}
}
if page.can_alloc(inserted_key, inserted_value) != 0 {
debug!("can alloc");
// We can allocate. Do we need to duplicate this
// page (because of RC or first_free)?
let needs_dup = page.first_free() + record_size(inserted_key, inserted_value) >
PAGE_SIZE_U16;
match page {
Cow::MutPage(ref mut page) if cursor.pointer < cursor.first_rc_level &&
!needs_dup => {
debug!("does not need dup");
// No, there will be no other references to
// this page after this method (`put`)
// returns. Here, simply insert.
// Update the right child from the previous split
// (if any, `inserted_left_child` is 0 else).
debug!("page right child: {:?}", cursor.current()[0]);
page.set_right_child(cursor.current()[0], inserted_left_child);
page.skiplist_insert_after_cursor(rng,
&mut cursor.current_mut().cursor,
inserted_key,
inserted_value,
inserted_right_child);
use PageT;
last_allocated = page.page_offset();
}
_ => {
debug!("needs dup {:?} {:?} {:?}",
cursor.pointer,
cursor.first_rc_level,
needs_dup);
// Yes, we do need to duplicate this
// page. Propagate RC to pages
// below.
let page = self.load_cow_page(cursor.current().page);
// Iterate over the page, incorporating the new element.
use PageT;
let it = Iter {
iter: page.iter_all().peekable(),
off: page.offset(cursor.current()[0] as isize),
next_is_extra: false,
extra_left: inserted_left_child,
extra: (Some((inserted_key, inserted_value)), inserted_right_child),
};
// Increase the RC of everyone, but the left
// side of the split (which was just
// allocated now).
let incr_rc = cursor.pointer >= cursor.first_rc_level;
last_allocated = try!(self.spread_on_one_page(rng,
it.map(|(b, c)| {
let fresh = c == inserted_left_child || c == inserted_right_child;
(b, c, incr_rc && !fresh, incr_rc)
})));
if cursor.pointer < cursor.first_rc_level {
unsafe {
// free of the current page.
self.free_page(cursor.current().page)
}
}
}
}
break;
} else {
// We cannot allocate, we need to split this page
debug!("cannot alloc");
let (left, right, sep_key, sep_value) = {
let it = Iter {
iter: page.iter_all().peekable(),
off: page.offset(cursor.current()[0] as isize),
next_is_extra: false,
extra_left: inserted_left_child,
extra: (Some((inserted_key, inserted_value)), inserted_right_child),
};
// We're going to add a page, hence
// FIRST_BINDING_SIZE more bytes will be
// needed.
let total = page.occupied() + record_size(key, value) + FIRST_BINDING_SIZE;
if cursor.pointer >= cursor.first_rc_level {
let it = it.map(|(b, c)| {
if c == inserted_left_child || c == inserted_right_child {
(b, c, false, true)
} else {
(b, c, true, true)
}
});
try!(self.spread_on_two_pages(rng, it, total))
} else {
let it = it.map(|(b, c)| (b, c, false, false));
try!(self.spread_on_two_pages(rng, it, total))
}
};
// Extend the lifetime of "inserted_key".
inserted_key = sep_key;
inserted_left_child = left;
inserted_right_child = right;
inserted_value = sep_value;
cursor.pointer -= 1;
if cursor.pointer == 0 {
// We've just split the root! we need to
// allocate a page to collect the two sides of
// the split.
last_allocated = try!(self.split_root(rng,
&mut cursor,
inserted_left_child,
inserted_right_child,
inserted_key,
inserted_value));
break;
}
}
}
}
debug!("freeing pages from {:?} to {:?} {:?} (inclusive)",
cursor.pointer + 1,
leaf_pointer,
cursor.first_rc_level);
// Now, cursor_pointer is the reference to a page that doesn't
// need to split anymore (possibly the new root).
// Free all split pages.
let last_free = std::cmp::min(leaf_pointer + 1, cursor.first_rc_level);
let first_free = std::cmp::min(cursor.pointer + 1, last_free);
for page_cursor in &cursor.stack[first_free..last_free] {
// free the page that was split.
let rc = self.rc(page_cursor.page);
if rc <= 1 {
debug!("Freeing {:?}", page_cursor.page);
try!(self.remove_rc(rng, page_cursor.page));
unsafe { self.free_page(page_cursor.page) }
} else {
debug!("Decrease RC for page {:?}, new rc: {:?}",
page_cursor.page,
rc - 1);
try!(self.set_rc(rng, page_cursor.page, rc - 1));
}
}
// In the above loop, `break` only occur after an insertion of
// a (key, value) with right child `inserted_right_child`. For
// the loop below to update the reference properly in the
// pages above, we need to update that child here (it might be
// 0 if we're still at the leaf).
// Has the root split?
if cursor.pointer > 0 {
cursor.stack[cursor.pointer].page = last_allocated;
cursor.pointer -= 1;
// The root has not split, the splits stopped earlier. There are remaining pages.
while cursor.pointer > 0 {
if cursor.pointer == cursor.first_rc_level {
let page = cursor.current().page;
let rc = self.rc(page);
if rc >= 2 {
try!(self.set_rc(rng, page, rc - 1));
}
}
try!(self.update_put::<R, K, V>(rng, &mut cursor));
cursor.pointer -= 1;
}
db.0 = cursor[1].page
} else {
// The root has split, no need to do anything.
debug!("the root has split");
db.0 = last_allocated
}
Ok(true)
}
fn update_put<R: Rng, K: Representable, V: Representable>(&mut self,
rng: &mut R,
cursor: &mut CursorStack)
-> Result<(), Error> {
use PageT;
let mut page = self.load_cow_page(cursor.current().page);
match page {
Cow::MutPage(ref mut p) if cursor.pointer < cursor.first_rc_level => {
p.set_right_child(cursor.current()[0], cursor[cursor.pointer + 1].page);
cursor.current_mut().page = p.offset;
}
Cow::MutPage(_) | Cow::Page(_) => {
// Here, the page needs to be CoWed.
let incr_rc = cursor.pointer >= cursor.first_rc_level;
let current_ptr = page.offset(cursor.current()[0] as isize);
let new_page =
try!(self.spread_on_one_page::<_, K, V, _>(rng,
page.iter_all()
.map(|(off, b, c)| {
// Both pages will survive, increase reference count.
if off != current_ptr {
(b, c, incr_rc, incr_rc)
} else {
let c = cursor[cursor.pointer + 1].page;
(b, c, false, incr_rc)
}
})));
// If nothing points to the page anymore, free.
if cursor.pointer < cursor.first_rc_level {
unsafe {
use PageT;
debug!("line {:?}, freeing {:?}", line!(), page.page_offset());
self.free_page(page.page_offset())
}
}
debug!("NEW_PAGE = {:?}", new_page);
cursor.current_mut().page = new_page;
}
}
Ok(())
}
}
/// Iterator on a page, plus a middle element immediately after `off`,
/// with a fixed left and right child.
pub struct Iter<'a, P: SkipListPage + 'a, K: Representable, V: Representable> {
iter: std::iter::Peekable<skiplist::Iter<'a, P, K, V>>,
off: *const u8,
next_is_extra: bool,
extra_left: u64,
extra: (Option<(K, V)>, u64),
}
impl<'a, P: SkipListPage + 'a, K: Representable, V: Representable> Iterator for Iter<'a, P, K, V> {
type Item = (Option<(K, V)>, u64);
fn next(&mut self) -> Option<Self::Item> {
if self.next_is_extra {
debug!("next_is_extra");
self.next_is_extra = false;
self.off = std::ptr::null();
Some(self.extra)
} else {
debug!("not next_is_extra");
if let Some((a, b, d)) = self.iter.next() {
// if a == self.off, the extra element is to be
// inserted immediately after this element. Set
// next_is_extra, and replace the current element's
// right child with extra's left child.
debug!("{:?}", a);
if a == self.off {
self.next_is_extra = true;
Some((b, self.extra_left))
} else {
Some((b, d))
}
} else {
debug!("finished, extra = {:?}", self.off);
None
}
}
}
}