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unix: use a heap for timers

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Replace the red-black tree with a heap.  The most common operation that
libuv performs on timers is looking up the first timer to expire.  With
a red-black tree, that operation is O(log n).  With a heap, it's O(1).
This commit is contained in:
Ben Noordhuis 2013-09-12 10:26:24 +02:00 committed by Saúl Ibarra Corretgé
parent fc40836f9a
commit f17c535b73
7 changed files with 284 additions and 32 deletions
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1
Makefile.am
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@ -25,6 +25,7 @@ lib_LTLIBRARIES = libuv.la
libuv_la_CFLAGS = @CFLAGS@
libuv_la_LDFLAGS = -no-undefined -version-info 11:0:0
libuv_la_SOURCES = src/fs-poll.c \
src/heap-inl.h \
src/inet.c \
src/queue.h \
src/uv-common.c \

1
Makefile.mingw
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@ -29,6 +29,7 @@ INCLUDES = include/stdint-msvc2008.h \
include/uv-version.h \
include/uv-win.h \
include/uv.h \
src/heap-inl.h \
src/queue.h \
src/uv-common.h \
src/win/atomicops-inl.h \

18
include/uv-unix.h
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@ -177,16 +177,16 @@ typedef struct {
void* idle_handles[2]; \
void* async_handles[2]; \
struct uv__async async_watcher; \
/* RB_HEAD(uv__timers, uv_timer_s) */ \
struct uv__timers { \
struct uv_timer_s* rbh_root; \
} timer_handles; \
struct { \
void* min; \
unsigned int nelts; \
} timer_heap; \
uint64_t timer_counter; \
uint64_t time; \
int signal_pipefd[2]; \
uv__io_t signal_io_watcher; \
uv_signal_t child_watcher; \
int emfile_fd; \
uint64_t timer_counter; \
UV_PLATFORM_LOOP_FIELDS \
#define UV_REQ_TYPE_PRIVATE /* empty */
@ -265,14 +265,8 @@ typedef struct {
int pending; \
#define UV_TIMER_PRIVATE_FIELDS \
/* RB_ENTRY(uv_timer_s) tree_entry; */ \
struct { \
struct uv_timer_s* rbe_left; \
struct uv_timer_s* rbe_right; \
struct uv_timer_s* rbe_parent; \
int rbe_color; \
} tree_entry; \
uv_timer_cb timer_cb; \
void* heap_node[3]; \
uint64_t timeout; \
uint64_t repeat; \
uint64_t start_id;

238
src/heap-inl.h Normal file
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@ -0,0 +1,238 @@
/* Copyright (c) 2013, Ben Noordhuis <info@bnoordhuis.nl>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#ifndef UV_SRC_HEAP_H_
#define UV_SRC_HEAP_H_
#include <stddef.h> /* NULL */
#if defined(__GNUC__)
# define HEAP_EXPORT(declaration) __attribute__((unused)) static declaration
#else
# define HEAP_EXPORT(declaration) static declaration
#endif
struct heap_node {
struct heap_node* left;
struct heap_node* right;
struct heap_node* parent;
};
/* A binary min heap. The usual properties hold: the root is the lowest
* element in the set, the height of the tree is at most log2(nodes) and
* it's always a complete binary tree.
*
* The heap function try hard to detect corrupted tree nodes at the cost
* of a minor reduction in performance. Compile with -DNDEBUG to disable.
*/
struct heap {
struct heap_node* min;
unsigned int nelts;
};
/* Return non-zero if a < b. */
typedef int (*heap_compare_fn)(const struct heap_node* a,
const struct heap_node* b);
/* Public functions. */
HEAP_EXPORT(void heap_init(struct heap* heap));
HEAP_EXPORT(struct heap_node* heap_min(const struct heap* heap));
HEAP_EXPORT(void heap_insert(struct heap* heap,
struct heap_node* newnode,
heap_compare_fn less_than));
HEAP_EXPORT(void heap_remove(struct heap* heap,
struct heap_node* node,
heap_compare_fn less_than));
HEAP_EXPORT(void heap_dequeue(struct heap* heap, heap_compare_fn less_than));
/* Implementation follows. */
HEAP_EXPORT(void heap_init(struct heap* heap)) {
heap->min = NULL;
heap->nelts = 0;
}
HEAP_EXPORT(struct heap_node* heap_min(const struct heap* heap)) {
return heap->min;
}
/* Swap parent with child. Child moves closer to the root, parent moves away. */
static void heap_node_swap(struct heap* heap,
struct heap_node* parent,
struct heap_node* child) {
struct heap_node* sibling;
struct heap_node t;
t = *parent;
*parent = *child;
*child = t;
parent->parent = child;
if (child->left == child) {
child->left = parent;
sibling = child->right;
} else {
child->right = parent;
sibling = child->left;
}
if (sibling != NULL)
sibling->parent = child;
if (parent->left != NULL)
parent->left->parent = parent;
if (parent->right != NULL)
parent->right->parent = parent;
if (child->parent == NULL)
heap->min = child;
else if (child->parent->left == parent)
child->parent->left = child;
else
child->parent->right = child;
}
HEAP_EXPORT(void heap_insert(struct heap* heap,
struct heap_node* newnode,
heap_compare_fn less_than)) {
struct heap_node** parent;
struct heap_node** child;
unsigned int path;
unsigned int n;
unsigned int k;
newnode->left = NULL;
newnode->right = NULL;
newnode->parent = NULL;
/* Calculate the path from the root to the insertion point. This is a min
* heap so we always insert at the left-most free node of the bottom row.
*/
path = 0;
for (k = 0, n = 1 + heap->nelts; n >= 2; k += 1, n /= 2)
path = (path << 1) | (n & 1);
/* Now traverse the heap using the path we calculated in the previous step. */
parent = child = &heap->min;
while (k > 0) {
parent = child;
if (path & 1)
child = &(*child)->right;
else
child = &(*child)->left;
path >>= 1;
k -= 1;
}
/* Insert the new node. */
newnode->parent = *parent;
*child = newnode;
heap->nelts += 1;
/* Walk up the tree and check at each node if the heap property holds.
* It's a min heap so parent < child must be true.
*/
while (newnode->parent != NULL && less_than(newnode, newnode->parent))
heap_node_swap(heap, newnode->parent, newnode);
}
HEAP_EXPORT(void heap_remove(struct heap* heap,
struct heap_node* node,
heap_compare_fn less_than)) {
struct heap_node* smallest;
struct heap_node** max;
struct heap_node* child;
unsigned int path;
unsigned int k;
unsigned int n;
if (heap->nelts == 0)
return;
/* Calculate the path from the min (the root) to the max, the left-most node
* of the bottom row.
*/
path = 0;
for (k = 0, n = heap->nelts; n >= 2; k += 1, n /= 2)
path = (path << 1) | (n & 1);
/* Now traverse the heap using the path we calculated in the previous step. */
max = &heap->min;
while (k > 0) {
if (path & 1)
max = &(*max)->right;
else
max = &(*max)->left;
path >>= 1;
k -= 1;
}
heap->nelts -= 1;
/* Unlink the max node. */
child = *max;
*max = NULL;
if (child == node) {
/* We're removing either the max or the last node in the tree. */
if (child == heap->min) {
heap->min = NULL;
}
return;
}
/* Replace the to be deleted node with the max node. */
child->left = node->left;
child->right = node->right;
child->parent = node->parent;
if (child->left != NULL) {
child->left->parent = child;
}
if (child->right != NULL) {
child->right->parent = child;
}
if (node->parent == NULL) {
heap->min = child;
} else if (node->parent->left == node) {
node->parent->left = child;
} else {
node->parent->right = child;
}
/* Walk down the subtree and check at each node if the heap property holds.
* It's a min heap so parent < child must be true. If the parent is bigger,
* swap it with the smallest child.
*/
for (;;) {
smallest = child;
if (child->left != NULL && less_than(smallest, child))
smallest = child->left;
if (child->right != NULL && less_than(smallest, child))
smallest = child->right;
if (smallest == child)
break;
heap_node_swap(heap, child, smallest);
}
}
HEAP_EXPORT(void heap_dequeue(struct heap* heap, heap_compare_fn less_than)) {
heap_remove(heap, heap->min, less_than);
}
#undef HEAP_EXPORT
#endif /* UV_SRC_HEAP_H_ */

3
src/unix/loop.c
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@ -22,6 +22,7 @@
#include "uv.h"
#include "tree.h"
#include "internal.h"
#include "heap-inl.h"
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
@ -80,7 +81,7 @@ static int uv__loop_init(uv_loop_t* loop, int default_loop) {
uv__signal_global_once_init();
memset(loop, 0, sizeof(*loop));
RB_INIT(&loop->timer_handles);
heap_init((struct heap*) &loop->timer_heap);
QUEUE_INIT(&loop->wq);
QUEUE_INIT(&loop->active_reqs);
QUEUE_INIT(&loop->idle_handles);

54
src/unix/timer.c
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@ -20,35 +20,41 @@
#include "uv.h"
#include "internal.h"
#include "heap-inl.h"
#include <assert.h>
#include <limits.h>
static int uv__timer_cmp(const uv_timer_t* a, const uv_timer_t* b) {
static int timer_less_than(const struct heap_node* ha,
const struct heap_node* hb) {
const uv_timer_t* a;
const uv_timer_t* b;
a = container_of(ha, const uv_timer_t, heap_node);
b = container_of(hb, const uv_timer_t, heap_node);
if (a->timeout < b->timeout)
return -1;
if (a->timeout > b->timeout)
return 1;
/*
* compare start_id when both has the same timeout. start_id is
* allocated with loop->timer_counter in uv_timer_start().
if (b->timeout < a->timeout)
return 0;
/* Compare start_id when both have the same timeout. start_id is
* allocated with loop->timer_counter in uv_timer_start().
*/
if (a->start_id < b->start_id)
return -1;
if (a->start_id > b->start_id)
return 1;
if (b->start_id < a->start_id)
return 0;
return 0;
}
RB_GENERATE_STATIC(uv__timers, uv_timer_s, tree_entry, uv__timer_cmp)
int uv_timer_init(uv_loop_t* loop, uv_timer_t* handle) {
uv__handle_init(loop, (uv_handle_t*)handle, UV_TIMER);
handle->timer_cb = NULL;
handle->repeat = 0;
return 0;
}
@ -72,7 +78,9 @@ int uv_timer_start(uv_timer_t* handle,
/* start_id is the second index to be compared in uv__timer_cmp() */
handle->start_id = handle->loop->timer_counter++;
RB_INSERT(uv__timers, &handle->loop->timer_handles, handle);
heap_insert((struct heap*) &handle->loop->timer_heap,
(struct heap_node*) &handle->heap_node,
timer_less_than);
uv__handle_start(handle);
return 0;
@ -83,7 +91,9 @@ int uv_timer_stop(uv_timer_t* handle) {
if (!uv__is_active(handle))
return 0;
RB_REMOVE(uv__timers, &handle->loop->timer_handles, handle);
heap_remove((struct heap*) &handle->loop->timer_heap,
(struct heap_node*) &handle->heap_node,
timer_less_than);
uv__handle_stop(handle);
return 0;
@ -114,15 +124,15 @@ uint64_t uv_timer_get_repeat(const uv_timer_t* handle) {
int uv__next_timeout(const uv_loop_t* loop) {
const struct heap_node* heap_node;
const uv_timer_t* handle;
uint64_t diff;
/* RB_MIN expects a non-const tree root. That's okay, it doesn't modify it. */
handle = RB_MIN(uv__timers, (struct uv__timers*) &loop->timer_handles);
if (handle == NULL)
heap_node = heap_min((const struct heap*) &loop->timer_heap);
if (heap_node == NULL)
return -1; /* block indefinitely */
handle = container_of(heap_node, const uv_timer_t, heap_node);
if (handle->timeout <= loop->time)
return 0;
@ -135,9 +145,15 @@ int uv__next_timeout(const uv_loop_t* loop) {
void uv__run_timers(uv_loop_t* loop) {
struct heap_node* heap_node;
uv_timer_t* handle;
while ((handle = RB_MIN(uv__timers, &loop->timer_handles))) {
for (;;) {
heap_node = heap_min((struct heap*) &loop->timer_heap);
if (heap_node == NULL)
break;
handle = container_of(heap_node, uv_timer_t, heap_node);
if (handle->timeout > loop->time)
break;

1
uv.gyp
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@ -63,6 +63,7 @@
'include/uv-errno.h',
'include/uv-version.h',
'src/fs-poll.c',
'src/heap-inl.h',
'src/inet.c',
'src/queue.h',
'src/uv-common.c',