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refactor and improve atomic bitmap usage

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This commit is contained in:
daan 2019-11-07 10:26:52 -08:00
parent b09282bc0d
commit 378716c467
10 changed files with 183 additions and 131 deletions
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110
src/bitmap.inc.c
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@ -1,41 +1,30 @@
/* ----------------------------------------------------------------------------
Copyright (c) 2019, Microsoft Research, Daan Leijen
This is free software; you can redistribute it and/or modify it under the
terms of the MIT license. A copy of the license can be found in the file
"LICENSE" at the root of this distribution.
-----------------------------------------------------------------------------*/
/* ----------------------------------------------------------------------------
This file is meant to be included in other files for efficiency.
It implements a bitmap that can set/reset sequences of bits atomically
and is used to concurrently claim memory ranges.
A bitmap is an array of fields where each field is a machine word (`uintptr_t`)
A current limitation is that the bit sequences cannot cross fields
and that the sequence must be smaller or equal to the bits in a field.
---------------------------------------------------------------------------- */
#pragma once
#ifndef MI_BITMAP_H
#define MI_BITMAP_H
#ifndef MI_BITMAP_C
#define MI_BITMAP_C
#include "mimalloc.h"
#include "mimalloc-internal.h"
// Use bit scan forward to quickly find the first zero bit if it is available
#if defined(_MSC_VER)
#define MI_HAVE_BITSCAN
#include <intrin.h>
static inline size_t mi_bsf(uintptr_t x) {
if (x==0) return 8*MI_INTPTR_SIZE;
DWORD idx;
MI_64(_BitScanForward)(&idx, x);
return idx;
}
static inline size_t mi_bsr(uintptr_t x) {
if (x==0) return 8*MI_INTPTR_SIZE;
DWORD idx;
MI_64(_BitScanReverse)(&idx, x);
return idx;
}
#elif defined(__GNUC__) || defined(__clang__)
#define MI_HAVE_BITSCAN
#if (INTPTR_MAX == LONG_MAX)
# define MI_L(x) x##l
#else
# define MI_L(x) x##ll
#endif
static inline size_t mi_bsf(uintptr_t x) {
return (x==0 ? 8*MI_INTPTR_SIZE : MI_L(__builtin_ctz)(x));
}
static inline size_t mi_bsr(uintptr_t x) {
return (x==0 ? 8*MI_INTPTR_SIZE : (8*MI_INTPTR_SIZE - 1) - MI_L(__builtin_clz)(x));
}
#endif
/* -----------------------------------------------------------
Bitmap definition
----------------------------------------------------------- */
#define MI_BITMAP_FIELD_BITS (8*MI_INTPTR_SIZE)
#define MI_BITMAP_FIELD_FULL (~((uintptr_t)0)) // all bits set
@ -63,14 +52,59 @@ static inline size_t mi_bitmap_index_bit_in_field(mi_bitmap_index_t bitmap_idx)
return (bitmap_idx % MI_BITMAP_FIELD_BITS);
}
// Get the full bit index
static inline size_t mi_bitmap_index_bit(mi_bitmap_index_t bitmap_idx) {
return bitmap_idx;
}
// The bit mask for a given number of blocks at a specified bit index.
static uintptr_t mi_bitmap_mask_(size_t count, size_t bitidx) {
mi_assert_internal(count + bitidx <= MI_BITMAP_FIELD_BITS);
return ((((uintptr_t)1 << count) - 1) << bitidx);
}
// Try to atomically claim a sequence of `count` bits in a single field at `idx` in `bitmap`.
// Returns `true` on success.
/* -----------------------------------------------------------
Use bit scan forward/reverse to quickly find the first zero bit if it is available
----------------------------------------------------------- */
#if defined(_MSC_VER)
#define MI_HAVE_BITSCAN
#include <intrin.h>
static inline size_t mi_bsf(uintptr_t x) {
if (x==0) return 8*MI_INTPTR_SIZE;
DWORD idx;
MI_64(_BitScanForward)(&idx, x);
return idx;
}
static inline size_t mi_bsr(uintptr_t x) {
if (x==0) return 8*MI_INTPTR_SIZE;
DWORD idx;
MI_64(_BitScanReverse)(&idx, x);
return idx;
}
#elif defined(__GNUC__) || defined(__clang__)
#include <limits.h> // LONG_MAX
#define MI_HAVE_BITSCAN
#if (INTPTR_MAX == LONG_MAX)
# define MI_L(x) x##l
#else
# define MI_L(x) x##ll
#endif
static inline size_t mi_bsf(uintptr_t x) {
return (x==0 ? 8*MI_INTPTR_SIZE : MI_L(__builtin_ctz)(x));
}
static inline size_t mi_bsr(uintptr_t x) {
return (x==0 ? 8*MI_INTPTR_SIZE : (8*MI_INTPTR_SIZE - 1) - MI_L(__builtin_clz)(x));
}
#endif
/* -----------------------------------------------------------
Claim a bit sequence atomically
----------------------------------------------------------- */
// Try to atomically claim a sequence of `count` bits in a single
// field at `idx` in `bitmap`. Returns `true` on success.
static inline bool mi_bitmap_try_claim_field(mi_bitmap_t bitmap, size_t idx, const size_t count, mi_bitmap_index_t* bitmap_idx)
{
mi_assert_internal(bitmap_idx != NULL);
@ -93,7 +127,7 @@ static inline bool mi_bitmap_try_claim_field(mi_bitmap_t bitmap, size_t idx, con
while (bitidx <= bitidx_max) {
if ((map & m) == 0) { // are the mask bits free at bitidx?
mi_assert_internal((m >> bitidx) == mask); // no overflow?
uintptr_t newmap = map | m;
const uintptr_t newmap = map | m;
mi_assert_internal((newmap^map) >> bitidx == mask);
if (!mi_atomic_cas_weak(field, newmap, map)) { // TODO: use strong cas here?
// no success, another thread claimed concurrently.. keep going
@ -109,10 +143,10 @@ static inline bool mi_bitmap_try_claim_field(mi_bitmap_t bitmap, size_t idx, con
else {
// on to the next bit range
#ifdef MI_HAVE_BITSCAN
size_t shift = (count == 1 ? 1 : mi_bsr(map & m) - bitidx + 1);
const size_t shift = (count == 1 ? 1 : mi_bsr(map & m) - bitidx + 1);
mi_assert_internal(shift > 0 && shift <= count);
#else
size_t shift = 1;
const size_t shift = 1;
#endif
bitidx += shift;
m <<= shift;