Hadrian: bump Cabal submodule, install extra dynamic flavours of RTS
[ghc.git] / rts / Arena.c
1 /* -----------------------------------------------------------------------------
2 (c) The University of Glasgow 2001
3
4 Arena allocation. Arenas provide fast memory allocation at the
5 expense of fine-grained recycling of storage: memory may be
6 only be returned to the system by freeing the entire arena, it
7 isn't possible to return individual objects within an arena.
8
9 Do not assume that sequentially allocated objects will be adjacent
10 in memory.
11
12 Quirks: this allocator makes use of the RTS block allocator. If
13 the current block doesn't have enough room for the requested
14 object, then a new block is allocated. This means that allocating
15 large objects will tend to result in wasted space at the end of
16 each block. In the worst case, half of the allocated space is
17 wasted. This allocator is therefore best suited to situations in
18 which most allocations are small.
19 -------------------------------------------------------------------------- */
20
21 #include "PosixSource.h"
22 #include "Rts.h"
23
24 #include "RtsUtils.h"
25 #include "Arena.h"
26
27 // Each arena struct is allocated using malloc().
28 struct _Arena {
29 bdescr *current;
30 StgWord *free; // ptr to next free byte in current block
31 StgWord *lim; // limit (== last free byte + 1)
32 };
33
34 // We like to keep track of how many blocks we've allocated for
35 // Storage.c:memInventory().
36 static long arena_blocks = 0;
37
38 // Begin a new arena
39 Arena *
40 newArena( void )
41 {
42 Arena *arena;
43
44 arena = stgMallocBytes(sizeof(Arena), "newArena");
45 arena->current = allocBlock_lock();
46 arena->current->link = NULL;
47 arena->free = arena->current->start;
48 arena->lim = arena->current->start + BLOCK_SIZE_W;
49 arena_blocks++;
50
51 return arena;
52 }
53
54 // The minimum alignment of an allocated block.
55 #define MIN_ALIGN 8
56
57 /* 'n' is assumed to be a power of 2 */
58 #define ROUNDUP(x,n) (((x)+((n)-1))&(~((n)-1)))
59 #define B_TO_W(x) ((x) / sizeof(W_))
60
61 // Allocate some memory in an arena
62 void *
63 arenaAlloc( Arena *arena, size_t size )
64 {
65 void *p;
66 uint32_t size_w;
67 uint32_t req_blocks;
68 bdescr *bd;
69
70 // round up to nearest alignment chunk.
71 size = ROUNDUP(size,MIN_ALIGN);
72
73 // size of allocated block in words.
74 size_w = B_TO_W(size);
75
76 if ( arena->free + size_w < arena->lim ) {
77 // enough room in the current block...
78 p = arena->free;
79 arena->free += size_w;
80 return p;
81 } else {
82 // allocate a fresh block...
83 req_blocks = (W_)BLOCK_ROUND_UP(size) / BLOCK_SIZE;
84 bd = allocGroup_lock(req_blocks);
85 arena_blocks += req_blocks;
86
87 bd->gen_no = 0;
88 bd->gen = NULL;
89 bd->dest_no = 0;
90 bd->flags = 0;
91 bd->free = bd->start;
92 bd->link = arena->current;
93 arena->current = bd;
94 arena->free = bd->free + size_w;
95 arena->lim = bd->free + bd->blocks * BLOCK_SIZE_W;
96 return bd->start;
97 }
98 }
99
100 // Free an entire arena
101 void
102 arenaFree( Arena *arena )
103 {
104 bdescr *bd, *next;
105
106 for (bd = arena->current; bd != NULL; bd = next) {
107 next = bd->link;
108 arena_blocks -= bd->blocks;
109 ASSERT(arena_blocks >= 0);
110 freeGroup_lock(bd);
111 }
112 stgFree(arena);
113 }
114
115 unsigned long
116 arenaBlocks( void )
117 {
118 return arena_blocks;
119 }