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r12338@catbus: nickm | 2007-04-10 20:29:05 -0400
Document memory pool implementation, and tweak it even mor. See? Programming is fun. svn:r9940
This commit is contained in:
parent
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commit
51e4b8d706
@ -6,6 +6,8 @@ Changes in version 0.2.0.1-alpha - 2007-??-??
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queue for each circuit. This lets us use less slack memory, and
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will eventually let us be smarter about prioritizing different kinds
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of traffic.
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- Allocate cells in memory pools better speed and memory efficiency,
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especially on platforms where malloc() is inefficient.
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- Stop reading on edge connections when their corresponding circuit
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buffers are full; start again as the circuits empty out.
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7
doc/TODO
7
doc/TODO
@ -75,7 +75,12 @@ Things we'd like to do in 0.2.0.x:
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[No need to do this: the edge-connection choking will already take
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care of this a bit, and rewriting the 'bridged connection' code
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to not use socketpairs will give us even more control.]
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- Do we switch to arena-allocation for cells?
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. Do we switch to pool-allocation for cells?
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o Implement pool-allocation
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o Have Tor use it for packed cells.
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o Document it.
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- Do something smart with freeing unused chunks.
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- Benchmark pool-allocation vs straightforward malloc.
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- Can we stop doing so many memcpys on cells?
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o Also, only package data from exitconns when there is space on the
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target OR conn's outbuf? or when the circuit is not too full.
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@ -1,6 +1,6 @@
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/* Copyright 2007 Nick Mathewson */
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/* See LICENSE for licensing information */
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/* $Id: /tor/trunk/src/common/util.c 12153 2007-03-12T03:11:12.797278Z nickm $ */
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/* $Id$ */
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#include <stdlib.h>
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#include <string.h>
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@ -8,10 +8,48 @@
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#include "mempool.h"
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/* OVERVIEW:
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* DOCDOC
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*/
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/* DRAWBACKS:
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*
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* This is an implementation of memory pools for Tor cells. It may be
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* useful for you too.
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*
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* Generally, a memory pool is an allocation strategy optimized for large
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* numbers of identically-sized objects. Rather than the elaborate arena
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* and coalescing strategeis you need to get good performance for a
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* general-purpose malloc(), pools use a series of large memory "chunks",
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* each of which is carved into a bunch of smaller "items" or
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* "allocations".
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*
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* To get decent performance, you need to:
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* - Minimize the number of times you hit the underlying allocator.
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* - Try to keep accesses as local in memory as possible.
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* - Try to keep the common case fast.
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*
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* Our implementation uses three lists of chunks per pool. Each chunk can
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* be either "full" (no more room for items); "empty" (no items); or
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* "used" (not full, not empty). There are independent doubly-linked
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* lists for each state.
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*
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* CREDIT:
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*
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* I wrote this after looking at 3 or 4 other pooling allocators, but
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* without copying. The strategy this most resembles (which is funny,
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* since that's the one I looked at longest ago) the pool allocator
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* underlying Python's obmalloc code. Major differences from obmalloc's
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* pools are:
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* - We don't even try to be threadsafe.
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* - We only handle objects of one size.
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* - Our list of empty chunks is doubly-linked, not singly-linked.
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* (This could change pretty easily; it's only doubly-linked for
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* consistency.)
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* - We keep a list of full chunks (so we can have a "nuke everything"
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* function). Obmalloc's pools leave full chunks to float unanchored.
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*
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* [XXXX020 Another way to support 'nuke everything' would be to keep
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* _all_ the chunks in a doubly-linked-list. This would have more
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* space overhead per chunk, but less pointer manipulation overhead
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* than the current approach.]
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*
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* LIMITATIONS:
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* - Not even slightly threadsafe.
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* - Likes to have lots of items per chunks.
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* - One pointer overhead per allocated thing. (The alternative is
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@ -24,12 +62,6 @@
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* - probably, chunks should always be a power of 2.
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*/
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/* NOTES:
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* - The algorithm is similar to the one used by Python, but assumes that
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* we'll know in advance which objects we want to pool, and doesn't
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* try to handle a zillion objects of weird different sizes.
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*/
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#if 1
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/* Tor dependencies */
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#include "orconfig.h"
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@ -39,8 +71,12 @@
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#define ALLOC(x) tor_malloc(x)
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#define FREE(x) tor_free(x)
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#define ASSERT(x) tor_assert(x)
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#undef ALLOC_CAN_RETURN_NULL
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/* End Tor dependencies */
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#else
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/* If you're not building this as part of Tor, you'll want to define the
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* following macros. For now, these should do as defaults.
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*/
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#include <assert.h>
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#define PREDICT_UNLIKELY(x) (x)
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#define PREDICT_LIKELY(x) (x)
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@ -49,63 +85,90 @@
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#define STRUCT_OFFSET(tp, member) \
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((off_t) (((char*)&((tp*)0)->member)-(char*)0))
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#define ASSERT(x) assert(x)
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#define ALLOC_CAN_RETURN_NULL
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#endif
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/* Tuning parameters */
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/** DOCDOC */
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/** Largest type that we need to ensure returned memory items are aligned to.
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* Change this to "double" if we need to be safe for structs with doubles. */
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#define ALIGNMENT_TYPE void *
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/** DOCDOC */
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#define ALIGNMENT sizeof(void*)
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/** DOCDOC */
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/** Increment that we need to align allocated */
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#define ALIGNMENT sizeof(ALIGNMENT_TYPE)
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/** Largest memory chunk that we should allocate. */
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#define MAX_CHUNK (8*(1L<<20))
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/** DOCDOC */
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/** Smallest memory chunk size that we should allocate. */
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#define MIN_CHUNK 4096
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typedef struct mp_allocated_t mp_allocated_t;
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typedef struct mp_chunk_t mp_chunk_t;
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/** DOCDOC */
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/** Holds a single allocated item, allocated as part of a chunk. */
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struct mp_allocated_t {
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/** The chunk that this item is allocated in. This adds overhead to each
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* allocated item, thus making this implementation inappropriate for
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* very small items. */
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mp_chunk_t *in_chunk;
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union {
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/** If this item is free, the next item on the free list. */
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mp_allocated_t *next_free;
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/** If this item is not free, the actual memory contents of this item.
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* (Not actual size.) */
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char mem[1];
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/** An extra element to the union to insure correct alignment. */
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ALIGNMENT_TYPE _dummy;
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};
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};
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/** DOCDOC */
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struct mp_chunk_t {
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unsigned long magic;
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mp_chunk_t *next;
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mp_chunk_t *prev;
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mp_pool_t *pool;
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mp_allocated_t *first_free;
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int n_allocated;
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int capacity;
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size_t mem_size;
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char *next_mem;
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char mem[1];
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};
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/** DOCDOC */
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/** 'Magic' value used to detect memory corruption. */
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#define MP_CHUNK_MAGIC 0x09870123
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/** DOCDOC */
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/** A chunk of memory. Chunks come from malloc; we use them */
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struct mp_chunk_t {
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unsigned long magic; /**< Must be MP_CHUNK_MAGIC if this chunk is valid. */
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mp_chunk_t *next; /**< The next free, used, or full chunk in sequence. */
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mp_chunk_t *prev; /**< The previous free, used, or full chunk in sequence. */
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mp_pool_t *pool; /**< The pool that this chunk is part of */
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/** First free item in the freelist for this chunk. Note that this may be
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* NULL even if this chunk is not at capacity: if so, the free memory at
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* next_mem has not yet been carved into items.
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*/
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mp_allocated_t *first_free;
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int n_allocated; /**< Number of currently allocated items in this chunk */
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int capacity; /**< Largest number of items that can be fit into this chunk */
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size_t mem_size; /**< Number of usable bytes in mem. */
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char *next_mem; /**< Pointer into part of <b>mem</b> not yet carved up. */
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char mem[1]; /**< Storage for this chunk. (Not actual size.) */
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};
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/** Number of extra bytes needed beyond mem_size to allocate a chunk. */
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#define CHUNK_OVERHEAD (sizeof(mp_chunk_t)-1)
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/** DOCDOC */
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/** Given a pointer to a mp_allocated_t, return a pointer to the memory
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* item it holds. */
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#define A2M(a) (&(a)->mem[0])
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/** DOCDOC */
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/** Given a pointer to a memory_item_t, return a pointer to its enclosing
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* mp_allocated_t. */
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#define M2A(p) ( ((char*)p) - STRUCT_OFFSET(mp_allocated_t, mem) )
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/* INVARIANT: every chunk can hold 2 or more items. */
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#ifdef ALLOC_CAN_RETURN_NULL
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/** If our ALLOC() macro can return NULL, check whether <b>x</b> is NULL,
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* and if so, return NULL. */
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#define CHECK_ALLOC(x) \
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if (PREDICT_UNLIKELY(!x)) { return NULL; }
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#else
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/** If our ALLOC() macro can't return NULL, do nothing. */
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#define CHECK_ALLOC(x)
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#endif
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/** DOCDOC */
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/** Helper: Allocate and return a new memory chunk for <b>pool</b>. Does not
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* link the chunk into any list. */
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static mp_chunk_t *
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mp_chunk_new(mp_pool_t *pool)
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{
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size_t sz = pool->new_chunk_capacity * pool->item_alloc_size;
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mp_chunk_t *chunk = ALLOC(CHUNK_OVERHEAD + sz);
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CHECK_ALLOC(chunk);
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memset(chunk, 0, sizeof(mp_chunk_t)); /* Doesn't clear the whole thing. */
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chunk->magic = MP_CHUNK_MAGIC;
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chunk->capacity = pool->new_chunk_capacity;
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@ -115,29 +178,44 @@ mp_chunk_new(mp_pool_t *pool)
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return chunk;
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}
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/** DOCDOC */
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/** Return an newly allocated item from <b>pool</b>. */
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void *
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mp_pool_get(mp_pool_t *pool)
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{
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mp_chunk_t *chunk;
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mp_allocated_t *allocated;
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if (PREDICT_LIKELY(pool->used_chunks != NULL)) {
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/* Common case: there is some chunk that is neither full nor empty. Use
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* that one. (We can't use the full ones, obviously, and we should fill
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* up the used ones before we start on any empty ones. */
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chunk = pool->used_chunks;
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} else if (pool->empty_chunks) {
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/* Put the most recently emptied chunk on the used list. */
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/* We have no used chunks, but we have an empty chunk that we haven't
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* freed yet: use that. (We pull from the front of the list, which should
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* get us the most recently emptied chunk.) */
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chunk = pool->empty_chunks;
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/* Remove the chunk from the empty list. */
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pool->empty_chunks = chunk->next;
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if (chunk->next)
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chunk->next->prev = NULL;
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/* Put the chunk on the 'used' list*/
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chunk->next = pool->used_chunks;
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if (chunk->next)
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chunk->next->prev = chunk;
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pool->used_chunks = chunk;
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ASSERT(!chunk->prev);
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--pool->n_empty_chunks;
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} else {
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/* Allocate a new chunk and add it to the used list. */
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/* We have no used or empty chunks: allocate a new chunk. */
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chunk = mp_chunk_new(pool);
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CHECK_ALLOC(chunk);
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/* Add the new chunk to the used list. */
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chunk->next = pool->used_chunks;
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if (chunk->next)
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chunk->next->prev = chunk;
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@ -148,40 +226,52 @@ mp_pool_get(mp_pool_t *pool)
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ASSERT(chunk->n_allocated < chunk->capacity);
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if (chunk->first_free) {
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/* If there's anything on the chunk's freelist, unlink it and use it. */
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allocated = chunk->first_free;
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chunk->first_free = allocated->next_free;
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allocated->next_free = NULL; /* debugging */
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allocated->next_free = NULL; /* For debugging; not really needed. */
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ASSERT(allocated->in_chunk == chunk);
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} else {
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/* Otherwise, the chunk had better have some free space left on it. */
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ASSERT(chunk->next_mem + pool->item_alloc_size <=
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chunk->mem + chunk->mem_size);
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/* Good, it did. Let's carve off a bit of that free space, and use
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* that. */
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allocated = (void*)chunk->next_mem;
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chunk->next_mem += pool->item_alloc_size;
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allocated->in_chunk = chunk;
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allocated->next_free = NULL; /* For debugging; not really needed. */
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}
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++chunk->n_allocated;
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if (PREDICT_UNLIKELY(chunk->n_allocated == chunk->capacity)) {
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/* This is now a full chunk. */
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/* This chunk just became full. */
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ASSERT(chunk == pool->used_chunks);
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ASSERT(chunk->prev == NULL);
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/* Take it off the used list. */
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pool->used_chunks = chunk->next;
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if (chunk->next)
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chunk->next->prev = NULL;
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/* Put it on the full list. */
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chunk->next = pool->full_chunks;
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if (chunk->next)
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chunk->next->prev = chunk;
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pool->full_chunks = chunk;
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}
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/* And return the memory portion of the mp_allocated_t. */
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return A2M(allocated);
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}
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/** DOCDOC */
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/** Return an allocated memory item to its memory pool. */
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void
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mp_pool_release(void *_item)
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mp_pool_release(void *item)
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{
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mp_allocated_t *allocated = (void*) M2A(_item);
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mp_allocated_t *allocated = (void*) M2A(item);
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mp_chunk_t *chunk = allocated->in_chunk;
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ASSERT(chunk);
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@ -194,7 +284,7 @@ mp_pool_release(void *_item)
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if (PREDICT_UNLIKELY(chunk->n_allocated == chunk->capacity)) {
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/* This chunk was full and is about to be used. */
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mp_pool_t *pool = chunk->pool;
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/* unlink from full */
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/* unlink from the full list */
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if (chunk->prev)
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chunk->prev->next = chunk->next;
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if (chunk->next)
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@ -202,7 +292,7 @@ mp_pool_release(void *_item)
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if (chunk == pool->full_chunks)
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pool->full_chunks = chunk->next;
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/* link to used */
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/* link to the used list. */
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chunk->next = pool->used_chunks;
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chunk->prev = NULL;
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if (chunk->next)
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@ -211,7 +301,8 @@ mp_pool_release(void *_item)
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} else if (PREDICT_UNLIKELY(chunk->n_allocated == 1)) {
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/* This was used and is about to be empty. */
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mp_pool_t *pool = chunk->pool;
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/* unlink from used */
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/* Unlink from the used list */
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if (chunk->prev)
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chunk->prev->next = chunk->next;
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if (chunk->next)
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@ -219,23 +310,26 @@ mp_pool_release(void *_item)
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if (chunk == pool->used_chunks)
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pool->used_chunks = chunk->next;
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/* link to empty */
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/* Link to the empty list */
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chunk->next = pool->empty_chunks;
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chunk->prev = NULL;
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if (chunk->next)
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chunk->next->prev = chunk;
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pool->empty_chunks = chunk;
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/* reset guts to defragment this chunk. */
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/* Reset the guts of this chunk to defragment it, in case it gets
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* used again. */
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chunk->first_free = NULL;
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chunk->next_mem = chunk->mem;
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++pool->n_empty_chunks;
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}
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--chunk->n_allocated;
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}
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/** DOCDOC */
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/** Allocate a new memory pool to hold items of size <b>item_size</b>. We'll
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* try to fit about <b>chunk_capacity</b> items in each chunk. */
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mp_pool_t *
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mp_pool_new(size_t item_size, size_t chunk_capacity)
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{
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@ -243,29 +337,35 @@ mp_pool_new(size_t item_size, size_t chunk_capacity)
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size_t alloc_size;
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pool = ALLOC(sizeof(mp_pool_t));
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CHECK_ALLOC(pool);
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memset(pool, 0, sizeof(mp_pool_t));
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/* First, minimal size with overhead. */
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/* First, we figure out how much space to allow per item. We'll want to
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* use make sure we have enough for the overhead plus the item size. */
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alloc_size = STRUCT_OFFSET(mp_allocated_t, mem) + item_size;
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/* If the item_size is less than sizeof(next_free), we need to make
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* the allocation bigger. */
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if (alloc_size < sizeof(mp_allocated_t))
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alloc_size = sizeof(mp_allocated_t);
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/* Then, round up to alignment. */
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/* If we're not an even multiple of ALIGNMENT, round up. */
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if (alloc_size % ALIGNMENT) {
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alloc_size = alloc_size + ALIGNMENT - (alloc_size % ALIGNMENT);
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}
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if (alloc_size < ALIGNMENT)
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alloc_size = ALIGNMENT;
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ASSERT((alloc_size % ALIGNMENT) == 0);
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/* Now we figure out how many items fit in each chunk. We need to fit at
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* least 2 items per chunk. No chunk can be more than MAX_CHUNK bytes long,
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* or less than MIN_CHUNK. */
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/* XXXX020 Try a bit harder here: we want to be a bit less than a power of
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2, not a bit over. */
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if (chunk_capacity > MAX_CHUNK)
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chunk_capacity = MAX_CHUNK;
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if (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)
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chunk_capacity = alloc_size * 2 + CHUNK_OVERHEAD;
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if (chunk_capacity < MIN_CHUNK) /* Guess system page size. */
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if (chunk_capacity < MIN_CHUNK)
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chunk_capacity = MIN_CHUNK;
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pool->new_chunk_capacity = (chunk_capacity-CHUNK_OVERHEAD) / alloc_size;
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@ -274,23 +374,33 @@ mp_pool_new(size_t item_size, size_t chunk_capacity)
|
||||
return pool;
|
||||
}
|
||||
|
||||
/** DOCDOC */
|
||||
/** If there are more than <b>n</b> empty chunks in <b>pool</b>, free the
|
||||
* exces ones that have been empty for the longest. */
|
||||
void
|
||||
mp_pool_clean(mp_pool_t *pool)
|
||||
mp_pool_clean(mp_pool_t *pool, int n)
|
||||
{
|
||||
if (pool->empty_chunks) {
|
||||
mp_chunk_t *next, *chunk = pool->empty_chunks->next;
|
||||
while (chunk) {
|
||||
next = chunk->next;
|
||||
FREE(chunk);
|
||||
chunk = next;
|
||||
}
|
||||
pool->empty_chunks->next = NULL;
|
||||
pool->n_empty_chunks = 1;
|
||||
mp_chunk_t *chunk, **first_to_free;
|
||||
first_to_free = &pool->empty_chunks;
|
||||
while (*first_to_free && n > 0) {
|
||||
first_to_free = &(*first_to_free)->next;
|
||||
--n;
|
||||
}
|
||||
if (!*first_to_free)
|
||||
return;
|
||||
|
||||
chunk = *first_to_free;
|
||||
while (chunk) {
|
||||
mp_chunk_t *next = chunk->next;
|
||||
chunk->magic = 0xdeadbeef;
|
||||
FREE(chunk);
|
||||
--pool->n_empty_chunks;
|
||||
chunk = next;
|
||||
}
|
||||
|
||||
*first_to_free = NULL;
|
||||
}
|
||||
|
||||
/** DOCDOC */
|
||||
/** Helper: Given a list of chunks, free all the chunks in the list. */
|
||||
static void
|
||||
destroy_chunks(mp_chunk_t *chunk)
|
||||
{
|
||||
@ -303,7 +413,8 @@ destroy_chunks(mp_chunk_t *chunk)
|
||||
}
|
||||
}
|
||||
|
||||
/** DOCDOC */
|
||||
/** Free all space held in <b>pool</b> This makes all pointers returned from
|
||||
* mp_pool_get(<b>pool</b>) invalid. */
|
||||
void
|
||||
mp_pool_destroy(mp_pool_t *pool)
|
||||
{
|
||||
@ -314,6 +425,7 @@ mp_pool_destroy(mp_pool_t *pool)
|
||||
FREE(pool);
|
||||
}
|
||||
|
||||
/** Helper: make sure that a given chunk list is not corrupt. */
|
||||
static int
|
||||
assert_chunks_ok(mp_pool_t *pool, mp_chunk_t *chunk, int empty, int full)
|
||||
{
|
||||
@ -353,6 +465,7 @@ assert_chunks_ok(mp_pool_t *pool, mp_chunk_t *chunk, int empty, int full)
|
||||
return n;
|
||||
}
|
||||
|
||||
/** Fail with an assertion if <b>pool</b> is not internally consistent. */
|
||||
void
|
||||
mp_pool_assert_ok(mp_pool_t *pool)
|
||||
{
|
||||
|
@ -1,6 +1,6 @@
|
||||
/* Copyright 2007 Nick Mathewson */
|
||||
/* See LICENSE for licensing information */
|
||||
/* $Id: /tor/trunk/src/common/util.c 12153 2007-03-12T03:11:12.797278Z nickm $ */
|
||||
/* $Id$ */
|
||||
|
||||
/**
|
||||
* \file util.h
|
||||
@ -10,25 +10,38 @@
|
||||
#ifndef MEMPOOL_H
|
||||
#define MEMPOOL_H
|
||||
|
||||
/** A memory pool is a context in which a large number of fixed-sized
|
||||
* objects can be allocated efficiently. See mempool.c for implementation
|
||||
* details. */
|
||||
typedef struct mp_pool_t mp_pool_t;
|
||||
|
||||
void *mp_pool_get(mp_pool_t *pool);
|
||||
void mp_pool_release(void *item);
|
||||
mp_pool_t *mp_pool_new(size_t item_size, unsigned int n_per_chunk);
|
||||
void mp_pool_clean(mp_pool_t *pool);
|
||||
void mp_pool_clean(mp_pool_t *pool, int n);
|
||||
void mp_pool_destroy(mp_pool_t *pool);
|
||||
void mp_pool_assert_ok(mp_pool_t *pool);
|
||||
|
||||
#ifdef MEMPOOL_PRIVATE
|
||||
typedef struct mp_chunk_t mp_chunk_t;
|
||||
/* These declarations are only used by mempool.c and test.c */
|
||||
|
||||
/** DOCDOC */
|
||||
struct mp_pool_t {
|
||||
mp_chunk_t *empty_chunks;
|
||||
mp_chunk_t *used_chunks;
|
||||
mp_chunk_t *full_chunks;
|
||||
/** Doubly-linked list of chunks in which no items have been allocated.
|
||||
* The front of the list is the most recently emptied chunk. */
|
||||
struct mp_chunk_t *empty_chunks;
|
||||
/** Doubly-linked list of chunks in which some items have been allocated,
|
||||
* but which are not yet full. The front of the list is the chunk that has
|
||||
* most recently been modified. */
|
||||
struct mp_chunk_t *used_chunks;
|
||||
/** Doubly-linked list of chunks in which no more items can be allocated.
|
||||
* The front of the list is the chunk that has most recently become full. */
|
||||
struct mp_chunk_t *full_chunks;
|
||||
/** Length of <b>empty_chunks</b>. */
|
||||
int n_empty_chunks;
|
||||
/** Size of each chunk (in items). */
|
||||
int new_chunk_capacity;
|
||||
/** Size to allocate for each item, including overhead and alignment
|
||||
* padding. */
|
||||
size_t item_alloc_size;
|
||||
};
|
||||
#endif
|
||||
|
@ -1479,8 +1479,8 @@ circuit_consider_sending_sendme(circuit_t *circ, crypt_path_t *layer_hint)
|
||||
#endif
|
||||
|
||||
#ifdef ENABLE_CELL_POOL
|
||||
static mp_pool_t *cell_pool;
|
||||
/* DOCDOC */
|
||||
static mp_pool_t *cell_pool = NULL;
|
||||
/** Allocate structures to hold cells. */
|
||||
void
|
||||
init_cell_pool(void)
|
||||
{
|
||||
@ -1488,7 +1488,7 @@ init_cell_pool(void)
|
||||
cell_pool = mp_pool_new(sizeof(packed_cell_t), 64);
|
||||
}
|
||||
|
||||
/* DOCDOC */
|
||||
/** Free all storage used to hold cells. */
|
||||
void
|
||||
free_cell_pool(void)
|
||||
{
|
||||
@ -1497,20 +1497,22 @@ free_cell_pool(void)
|
||||
cell_pool = NULL;
|
||||
}
|
||||
|
||||
/** Release storage held by <b>cell</b> */
|
||||
/** Release storage held by <b>cell</b>. */
|
||||
static INLINE void
|
||||
packed_cell_free(packed_cell_t *cell)
|
||||
{
|
||||
mp_pool_release(cell);
|
||||
}
|
||||
|
||||
/* DOCDOC */
|
||||
static INLINE packed_cell_t*
|
||||
/** Allocate and return a new packed_cell_t. */
|
||||
static INLINE packed_cell_t *
|
||||
packed_cell_alloc(void)
|
||||
{
|
||||
return mp_pool_get(cell_pool);
|
||||
}
|
||||
#else
|
||||
/* ENABLE_CELL_POOL isn't defined: here are some stubs to use tor_malloc()
|
||||
* and tor_free() instead. */
|
||||
void
|
||||
init_cell_pool(void)
|
||||
{
|
||||
|
@ -2142,13 +2142,15 @@ test_mempool(void)
|
||||
//mp_pool_assert_ok(pool);
|
||||
}
|
||||
if (crypto_rand_int(777)==0)
|
||||
mp_pool_clean(pool);
|
||||
mp_pool_clean(pool, 2);
|
||||
|
||||
if (i % 777)
|
||||
mp_pool_assert_ok(pool);
|
||||
}
|
||||
SMARTLIST_FOREACH(allocated, void *, m, mp_pool_release(m));
|
||||
mp_pool_assert_ok(pool);
|
||||
mp_pool_clean(pool, 0);
|
||||
mp_pool_assert_ok(pool);
|
||||
mp_pool_destroy(pool);
|
||||
smartlist_free(allocated);
|
||||
}
|
||||
|
Loading…
Reference in New Issue
Block a user