-
-
Notifications
You must be signed in to change notification settings - Fork 694
/
quantizer.d
331 lines (300 loc) · 11.4 KB
/
quantizer.d
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
// Written in the D programming language.
/**
Source: $(PHOBOSSRC std/experimental/allocator/building_blocks/quantizer.d)
*/
module std.experimental.allocator.building_blocks.quantizer;
import std.experimental.allocator.common;
/**
This allocator sits on top of `ParentAllocator` and quantizes allocation sizes,
usually from arbitrary positive numbers to a small set of round numbers (e.g.
powers of two, page sizes etc). This technique is commonly used to:
$(UL
$(LI Preallocate more memory than requested such that later on, when
reallocation is needed (e.g. to grow an array), expansion can be done quickly
in place. Reallocation to smaller sizes is also fast (in-place) when the new
size requested is within the same quantum as the existing size. Code that's
reallocation-heavy can therefore benefit from fronting a generic allocator with
a `Quantizer`. These advantages are present even if `ParentAllocator` does not
support reallocation at all.)
$(LI Improve behavior of allocators sensitive to allocation sizes, such as
`FreeList` and `FreeTree`. Rounding allocation requests up makes for smaller
free lists/trees at the cost of slack memory (internal fragmentation).)
)
The following methods are forwarded to the parent allocator if present:
`allocateAll`, `owns`, `deallocateAll`, `empty`.
Preconditions: `roundingFunction` must satisfy three constraints. These are
not enforced (save for the use of `assert`) for the sake of efficiency.
$(OL
$(LI $(D roundingFunction(n) >= n) for all `n` of type `size_t`;)
$(LI `roundingFunction` must be monotonically increasing, i.e. $(D
roundingFunction(n1) <= roundingFunction(n2)) for all $(D n1 < n2);)
$(LI `roundingFunction` must be `nothrow`, `@safe`, `@nogc` and `pure`, i.e.
always return the same value for a given `n`.)
)
*/
struct Quantizer(ParentAllocator, alias roundingFunction)
{
import std.traits : hasMember;
/**
The parent allocator. Depending on whether `ParentAllocator` holds state
or not, this is a member variable or an alias for
`ParentAllocator.instance`.
*/
static if (stateSize!ParentAllocator)
{
ParentAllocator parent;
}
else
{
alias parent = ParentAllocator.instance;
__gshared Quantizer instance;
}
/**
Returns `roundingFunction(n)`.
*/
size_t goodAllocSize(size_t n)
{
auto result = roundingFunction(n);
assert(result >= n);
return result;
}
/**
Alignment is identical to that of the parent.
*/
enum alignment = ParentAllocator.alignment;
/**
Gets a larger buffer `buf` by calling
`parent.allocate(goodAllocSize(n))`. If `buf` is `null`, returns
`null`. Otherwise, returns $(D buf[0 .. n]).
*/
void[] allocate(size_t n)
{
auto result = parent.allocate(goodAllocSize(n));
return result.ptr ? result.ptr[0 .. n] : null;
}
static if (hasMember!(ParentAllocator, "allocateZeroed"))
package(std) void[] allocateZeroed()(size_t n)
{
auto result = parent.allocateZeroed(goodAllocSize(n));
return result.ptr ? result.ptr[0 .. n] : null;
}
/**
Defined only if `parent.alignedAllocate` exists and works similarly to
`allocate` by forwarding to
$(D parent.alignedAllocate(goodAllocSize(n), a)).
*/
static if (hasMember!(ParentAllocator, "alignedAllocate"))
void[] alignedAllocate(size_t n, uint a)
{
auto result = parent.alignedAllocate(goodAllocSize(n), a);
return result.ptr ? result.ptr[0 .. n] : null;
}
/**
First checks whether there's enough slack memory preallocated for `b`
by evaluating $(D b.length + delta <= goodAllocSize(b.length)). If that's
the case, expands `b` in place. Otherwise, attempts to use
`parent.expand` appropriately if present.
*/
bool expand(ref void[] b, size_t delta)
{
if (!b || delta == 0) return delta == 0;
immutable allocated = goodAllocSize(b.length),
needed = b.length + delta,
neededAllocation = goodAllocSize(needed);
assert(b.length <= allocated);
assert(needed <= neededAllocation);
assert(allocated <= neededAllocation);
// Second test needed because expand must work for null pointers, too.
if (allocated == neededAllocation)
{
// Nice!
b = (() @trusted => b.ptr[0 .. needed])();
return true;
}
// Hail Mary
static if (hasMember!(ParentAllocator, "expand"))
{
// Expand to the appropriate quantum
auto original = (() @trusted => b.ptr[0 .. allocated])();
assert(goodAllocSize(needed) >= allocated);
if (!parent.expand(original, neededAllocation - allocated))
return false;
// Dial back the size
b = (() @trusted => original.ptr[0 .. needed])();
return true;
}
else
{
return false;
}
}
/**
Expands or shrinks allocated block to an allocated size of $(D
goodAllocSize(s)). Expansion occurs in place under the conditions required
by `expand`. Shrinking occurs in place if $(D goodAllocSize(b.length)
== goodAllocSize(s)).
*/
bool reallocate(ref void[] b, size_t s)
{
if (!b.ptr)
{
b = allocate(s);
return b.length == s;
}
if (s >= b.length && expand(b, s - b.length)) return true;
immutable toAllocate = goodAllocSize(s),
allocated = goodAllocSize(b.length);
// Are the lengths within the same quantum?
if (allocated == toAllocate)
{
// Reallocation (whether up or down) will be done in place
b = b.ptr[0 .. s];
return true;
}
// Defer to parent (or global) with quantized size
auto original = b.ptr[0 .. allocated];
if (!parent.reallocate(original, toAllocate)) return false;
b = original.ptr[0 .. s];
return true;
}
/**
Defined only if `ParentAllocator.alignedAllocate` exists. Expansion
occurs in place under the conditions required by `expand`. Shrinking
occurs in place if $(D goodAllocSize(b.length) == goodAllocSize(s)).
*/
static if (hasMember!(ParentAllocator, "alignedAllocate"))
bool alignedReallocate(ref void[] b, size_t s, uint a)
{
if (!b.ptr)
{
b = alignedAllocate(s, a);
return b.length == s;
}
if (s >= b.length && b.ptr.alignedAt(a) && expand(b, s - b.length)) return true;
immutable toAllocate = goodAllocSize(s),
allocated = goodAllocSize(b.length);
// Are the lengths within the same quantum?
if (allocated == toAllocate && b.ptr.alignedAt(a))
{
assert(b.ptr); // code above must have caught this
// Reallocation (whether up or down) will be done in place
b = b.ptr[0 .. s];
return true;
}
// Defer to parent (or global) with quantized size
auto original = b.ptr[0 .. allocated];
if (!parent.alignedReallocate(original, toAllocate, a)) return false;
b = original.ptr[0 .. s];
return true;
}
/**
Defined if `ParentAllocator.deallocate` exists and forwards to
$(D parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)])).
*/
static if (hasMember!(ParentAllocator, "deallocate"))
bool deallocate(void[] b)
{
if (!b.ptr) return true;
return parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)]);
}
// Forwarding methods
mixin(forwardToMember("parent",
"allocateAll", "owns", "deallocateAll", "empty"));
}
///
@system unittest
{
import std.experimental.allocator.building_blocks.free_tree : FreeTree;
import std.experimental.allocator.gc_allocator : GCAllocator;
size_t roundUpToMultipleOf(size_t s, uint base)
{
auto rem = s % base;
return rem ? s + base - rem : s;
}
// Quantize small allocations to a multiple of cache line, large ones to a
// multiple of page size
alias MyAlloc = Quantizer!(
FreeTree!GCAllocator,
n => roundUpToMultipleOf(n, n <= 16_384 ? 64 : 4096));
MyAlloc alloc;
const buf = alloc.allocate(256);
assert(buf.ptr);
}
@system unittest
{
import std.experimental.allocator.gc_allocator : GCAllocator;
alias MyAlloc = Quantizer!(GCAllocator,
(size_t n) => n.roundUpToMultipleOf(64));
testAllocator!(() => MyAlloc());
assert((() pure nothrow @safe @nogc => MyAlloc().goodAllocSize(1))() == 64);
auto a = MyAlloc();
auto b = a.allocate(42);
assert(b.length == 42);
// Inplace expand, since goodAllocSize is 64
assert((() @safe => a.expand(b, 22))());
//assert((() nothrow @safe => a.expand(b, 22))());
assert(b.length == 64);
// Trigger parent.expand, which may or may not succed
//() nothrow @safe { a.expand(b, 1); }();
() @safe { a.expand(b, 1); }();
assert(a.reallocate(b, 100));
assert(b.length == 100);
// Ensure deallocate inherits from parent
() nothrow @nogc { a.deallocate(b); }();
}
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.mallocator : Mallocator;
import std.typecons : Ternary;
alias Alloc = Quantizer!(Region!(Mallocator),
(size_t n) => n.roundUpToMultipleOf(64));
auto a = Alloc(Region!Mallocator(1024 * 64));
const b = a.allocate(42);
assert(b.length == 42);
// Check that owns inherits from parent, i.e. Region
assert((() pure nothrow @safe @nogc => a.owns(b))() == Ternary.yes);
assert((() pure nothrow @safe @nogc => a.owns(null))() == Ternary.no);
auto c = a.allocate(42);
assert(c.length == 42);
assert((() pure nothrow @safe @nogc => a.owns(c))() == Ternary.yes);
// Inplace expand, since goodAllocSize is 64
assert((() nothrow @safe => a.expand(c, 22))());
assert(c.length == 64);
// Trigger parent.expand
assert((() nothrow @safe => a.expand(c, 1))());
assert(c.length == 65);
// Check that reallocate inherits from parent
assert((() nothrow @nogc => a.reallocate(c, 100))());
assert(c.length == 100);
}
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.mallocator : Mallocator;
alias MyAlloc = Quantizer!(Region!(Mallocator),
(size_t n) => n.roundUpToMultipleOf(64));
testAllocator!(() => MyAlloc(Region!Mallocator(1024 * 64)));
auto a = MyAlloc(Region!Mallocator(1024 * 64));
void[] b;
assert((() nothrow @nogc => a.alignedReallocate(b, 42, 16))());
assert(b.length == 42);
assert(alignedAt(&b[0], 16));
}
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.typecons : Ternary;
alias MyAlloc = Quantizer!(Region!(),
(size_t n) => n.roundUpToMultipleOf(64));
testAllocator!(() => MyAlloc(Region!()(new ubyte[1024 * 64])));
auto a = MyAlloc(Region!()(new ubyte[1024 * 64]));
// Check that empty inherits from parent
assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
auto b = a.allocate(42);
assert(b.length == 42);
assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.no);
// Check that deallocateAll inherits from parent
assert((() nothrow @nogc => a.deallocateAll())());
assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
}