Merge pull request #161 from pesco/sloballoc

add SLOB allocator

src/SConscript

@@ -66,7 +66,8 @@ misc_hammer_parts = [
     'hammer.c',
     'pprint.c',
     'registry.c',
-    'system_allocator.c']
+    'system_allocator.c',
+    'sloballoc.c']
 
 if env['PLATFORM'] == 'win32':
     misc_hammer_parts += [
@@ -82,6 +83,7 @@ ctests = ['t_benchmark.c',
           't_parser.c',
           't_grammar.c',
           't_misc.c',
+          't_mm.c',
           't_regression.c']
 
 

src/hammer.h

@@ -804,6 +804,9 @@ HTokenType h_get_token_type_number(const char* name);
 const char* h_get_token_type_name(HTokenType token_type);
 // }}}
 
+/// Make an allocator that draws from the given memory area.
+HAllocator *h_sloballoc(void *mem, size_t size);
+
 #ifdef __cplusplus
 }
 #endif

src/sloballoc.c

@@ -0,0 +1,216 @@
+// first-fit SLOB (simple list of blocks) allocator
+
+#include "sloballoc.h"
+#include <stdint.h>
+#include <assert.h>
+
+struct alloc {
+    size_t size;
+    uint8_t data[];
+};
+
+struct block {
+    size_t size; // read: struct alloc
+    struct block *next;
+};
+
+struct slob {
+    size_t size;
+    struct block *head;
+    uint8_t data[];
+};
+
+
+SLOB *slobinit(void *mem, size_t size)
+{
+    SLOB *slob = mem;
+
+    assert(size >= sizeof(SLOB) + sizeof(struct block));
+    assert(size < UINTPTR_MAX - (uintptr_t)mem);
+
+    slob = mem;
+    slob->size = size - sizeof(SLOB);
+    slob->head = (struct block *)((uint8_t *)mem + sizeof(SLOB));
+    slob->head->size = slob->size - sizeof(struct alloc);
+    slob->head->next = NULL;
+
+    return slob;
+}
+
+void *sloballoc(SLOB *slob, size_t size)
+{
+    struct block *b, **p;
+    size_t fitblock, remblock;
+
+    // size must be enough to extend to a struct block in case of free
+    fitblock = sizeof(struct block) - sizeof(struct alloc);
+    if(size < fitblock) size = fitblock;
+
+    // need this much to fit another block in the remaining space
+    remblock = size + sizeof(struct block);
+    if(remblock < size) return NULL;    // overflow
+
+    // scan list for the first block of sufficient size
+    for(p=&slob->head; (b=*p); p=&b->next) {
+        if(b->size >= remblock) {
+            // cut from the end of the block
+            b->size -= sizeof(struct alloc) + size;
+            struct alloc *a = (struct alloc *)(((struct alloc *)b)->data + b->size);
+            a->size = size;
+            return a->data;
+        } else if(b->size >= size) {
+            // when a block fills, it converts directly to a struct alloc
+            *p = b->next;       // unlink
+            return ((struct alloc *)b)->data;
+        }
+    }
+
+    return NULL;
+}
+
+void slobfree(SLOB *slob, void *a_)
+{
+    struct alloc *a = (struct alloc *)((uint8_t *)a_ - sizeof(struct alloc));
+    struct block *b, **p, *left=NULL, *right=NULL, **rightp=NULL;
+
+    // sanity check: a lies inside slob
+    assert((uint8_t *)a >= slob->data);
+    assert(a->data + a->size <= slob->data + slob->size);
+
+    // scan list for blocks adjacent to a
+    for(p=&slob->head; (b=*p); p=&b->next) {
+        if((uint8_t *)a == ((struct alloc *)b)->data + b->size) {
+            assert(!left);
+            left = b;
+        }
+        if(a->data + a->size == (uint8_t *)b) {
+            assert(!right);
+            right = b;
+            rightp = p;
+        }
+
+        if(left && right) {
+            // extend left and unlink right
+            left->size += sizeof(*a) + a->size +
+                          sizeof(struct alloc) + right->size;
+            *rightp = right->next;
+            return;
+        }
+    }
+
+    if(left) {
+        // extend left to absorb a
+        left->size += sizeof(*a) + a->size;
+    } else if(right) {
+        // shift and extend right to absorb a
+        right->size += sizeof(*a) + a->size;
+        *rightp = (struct block *)a; **rightp = *right;
+    } else {
+        // spawn new block over a
+        struct block *b = (struct block *)a;
+        b->next = slob->head; slob->head = b;
+    }
+}
+
+int slobcheck(SLOB *slob)
+{
+    // invariants:
+    // 1. memory area is divided seamlessly and exactly into n blocks
+    // 2. every block is large enough to hold a 'struct block'.
+    // 3. free list has at most n elements.
+    // 4. every element of the free list is one of the valid blocks.
+    // 5. every block appears at most once in the free list.
+
+    uint8_t *p;
+    size_t nblocks=0, nfree=0;
+
+    #define FORBLOCKS \
+        for(p = slob->data; \
+            p != slob->data + slob->size; \
+            p += sizeof(struct alloc) + ((struct alloc *)p)->size)
+
+    // 1. memory area is divided seamlessly and exactly into n blocks
+    FORBLOCKS {
+        if(p < slob->data)
+            return 1;
+        if(p > slob->data + slob->size)
+            return 2;
+        nblocks++;
+
+        struct alloc *a = (struct alloc *)p;
+        if(a->size > UINTPTR_MAX - (uintptr_t)p)
+            return 3;
+
+        // 2. every block is large enough to hold a 'struct block'.
+        if(a->size + sizeof(struct alloc) < sizeof(struct block))
+            return 4;
+    }
+
+    // 3. free list has at most n elements.
+    for(struct block *b=slob->head; b; b=b->next) {
+        nfree++;
+        if(nfree > nblocks)
+            return 5;
+
+        // 4. every element of the free list is one of the valid blocks.
+        FORBLOCKS
+            if(p == (uint8_t *)b) break;
+        if(!p)
+            return 6;
+    }
+
+    // 5. every block appears at most once in the free list.
+    FORBLOCKS {
+        size_t count=0;
+        for(struct block *b=slob->head; b; b=b->next)
+            if(p == (uint8_t *)b) count++;
+        if(count > 1)
+            return 7;
+    }
+
+    #undef FORBLOCKS
+    return 0;
+}
+
+
+// hammer interface
+
+#include "hammer.h"
+
+static void *h_slob_alloc(HAllocator *mm, size_t size)
+{
+    SLOB *slob = (SLOB *)(mm+1);
+    return sloballoc(slob, size);
+}
+
+static void h_slob_free(HAllocator *mm, void *p)
+{
+    SLOB *slob = (SLOB *)(mm+1);
+    slobfree(slob, p);
+}
+
+static void *h_slob_realloc(HAllocator *mm, void *p, size_t size)
+{
+    SLOB *slob = (SLOB *)(mm+1);
+
+    assert(((void)"XXX need realloc for SLOB allocator", 0));
+    return NULL;
+}
+
+HAllocator *h_sloballoc(void *mem, size_t size)
+{
+    if(size < sizeof(HAllocator))
+        return NULL;
+
+    HAllocator *mm = mem;
+    SLOB *slob = slobinit((uint8_t *)mem + sizeof(HAllocator), size - sizeof(HAllocator));
+    if(!slob)
+        return NULL;
+    assert(slob == (SLOB *)(mm+1));
+
+    mm->alloc = h_slob_alloc;
+    mm->realloc = h_slob_realloc;
+    mm->free = h_slob_free;
+
+    return mm;
+}

src/sloballoc.h

@@ -0,0 +1,15 @@
+#ifndef SLOBALLOC_H_SEEN
+#define SLOBALLOC_H_SEEN
+
+#include <stddef.h>
+
+typedef struct slob SLOB;
+
+SLOB *slobinit(void *mem, size_t size);
+void *sloballoc(SLOB *slob, size_t size);
+void slobfree(SLOB *slob, void *p);
+
+// consistency check (verify internal invariants); returns 0 on success
+int slobcheck(SLOB *slob);
+
+#endif // SLOBALLOC_H_SEEN

src/t_mm.c

@@ -0,0 +1,148 @@
+#include <glib.h>
+#include <string.h>
+#include "test_suite.h"
+#include "sloballoc.h"
+#include "hammer.h"
+
+#define check_sloballoc_invariants() do {                                   \
+    int err = slobcheck(slob);                                              \
+    if(err) {                                                               \
+      g_test_message("SLOB invariant check failed on line %d, returned %d", \
+                     __LINE__, err);                                        \
+      g_test_fail();                                                        \
+    }                                                                       \
+  } while(0)
+
+#define check_sloballoc(VAR, SIZE, OFFSET) do { \
+    check_sloballoc_invariants();               \
+    VAR = sloballoc(slob, (SIZE));              \
+    g_check_cmp_ptr(VAR, ==, mem + (OFFSET));     \
+  } while(0)
+
+#define check_sloballoc_fail(SIZE) do { \
+    check_sloballoc_invariants();       \
+    void *p = sloballoc(slob, (SIZE));  \
+    g_check_cmp_ptr(p, ==, NULL);         \
+  } while(0)
+
+#define check_slobfree(P) do {      \
+    check_sloballoc_invariants();   \
+    slobfree(slob, P);              \
+  } while(0)
+
+#define N 1024
+
+#define SLOBALLOC_FIXTURE                                                   \
+    static uint8_t mem[N] = {0x58};                                         \
+    SLOB *slob = slobinit(mem, N);                                          \
+    size_t max = N - 2*sizeof(size_t) - sizeof(void *);                     \
+    (void)max;  /* silence warning */                                       \
+    if(!slob) {                                                             \
+        g_test_message("SLOB allocator init failed on line %d", __LINE__);  \
+        g_test_fail();                                                      \
+    }
+
+static void test_sloballoc_size(void)
+{
+    SLOBALLOC_FIXTURE
+    void *p;
+
+    check_sloballoc(p, max, N-max);
+    check_slobfree(p);
+
+    check_sloballoc_fail(N);
+    check_sloballoc_fail(max+1);
+
+    check_sloballoc(p, max, N-max);
+    check_slobfree(p);
+
+    check_sloballoc_invariants();
+}
+
+static void test_sloballoc_merge(void)
+{
+    SLOBALLOC_FIXTURE
+    void *p, *q, *r;
+
+    check_sloballoc(p, 100, N-100);
+    check_slobfree(p);
+    check_sloballoc(p, max, N-max);
+    check_slobfree(p);
+
+    check_sloballoc(p, 100, N-100);
+    check_sloballoc(q, 100, N-200-sizeof(size_t));
+    check_slobfree(p);
+    check_sloballoc(p,  50, N-50);
+    check_sloballoc(r, 100, N-300-2*sizeof(size_t));
+    check_slobfree(q);
+    check_sloballoc(q, 150, N-200-sizeof(size_t));
+    check_slobfree(p);
+    check_slobfree(r);
+    check_slobfree(q);  // merge left and right
+
+    check_sloballoc_fail(max+1);
+    check_sloballoc(p, max, N-max);
+    check_slobfree(p);
+
+    check_sloballoc_invariants();
+}
+
+static void test_sloballoc_small(void)
+{
+    SLOBALLOC_FIXTURE
+    void *p, *q, *r;
+
+    check_sloballoc(p, 100, N-100);
+    check_sloballoc(q,   1, N-100-sizeof(size_t)-sizeof(void *));
+    check_sloballoc(r, 100, N-200-2*sizeof(size_t)-sizeof(void *));
+    check_slobfree(q);
+    check_sloballoc(q,   1, N-100-sizeof(size_t)-sizeof(void *));
+    check_slobfree(p);
+    check_slobfree(r);
+
+    check_sloballoc_invariants();
+}
+
+#define check_h_sloballoc(VAR, SIZE, OFFSET) do {   \
+    check_sloballoc_invariants();                   \
+    VAR = mm->alloc(mm, (SIZE));                    \
+    g_check_cmp_ptr(VAR, ==, mem + (OFFSET));         \
+  } while(0)
+
+#define check_h_slobfree(P) do {    \
+    check_sloballoc_invariants();   \
+    mm->free(mm, P);                \
+  } while(0)
+
+static void test_sloballoc_hammer(void)
+{
+    static uint8_t mem[N] = {0x58};
+    HAllocator *mm = h_sloballoc(mem, N); int line = __LINE__;
+    SLOB *slob = ((void *)mm) + sizeof(HAllocator);
+    void *p, *q, *r;
+
+    if(!mm) {
+        g_test_message("h_sloballoc() failed on line %d", line);
+        g_test_fail();
+    }
+
+    check_h_sloballoc(p, 100, N-100);
+    check_h_sloballoc(q,   1, N-100-sizeof(size_t)-sizeof(void *));
+    check_h_sloballoc(r, 100, N-200-2*sizeof(size_t)-sizeof(void *));
+    check_h_slobfree(q);
+    check_h_sloballoc(q,   1, N-100-sizeof(size_t)-sizeof(void *));
+    check_h_slobfree(p);
+    check_h_slobfree(r);
+
+    check_sloballoc_invariants();
+}
+
+#undef N
+
+void register_mm_tests(void) {
+    g_test_add_func("/core/mm/sloballoc/size", test_sloballoc_size);
+    g_test_add_func("/core/mm/sloballoc/merge", test_sloballoc_merge);
+    g_test_add_func("/core/mm/sloballoc/small", test_sloballoc_small);
+    g_test_add_func("/core/mm/sloballoc/hammer", test_sloballoc_hammer);
+}
+

src/test_suite.c

@@ -24,6 +24,7 @@ extern void register_bitwriter_tests();
 extern void register_parser_tests();
 extern void register_grammar_tests();
 extern void register_misc_tests();
+extern void register_mm_tests();
 extern void register_benchmark_tests();
 extern void register_regression_tests();
 
@@ -36,6 +37,7 @@ int main(int argc, char** argv) {
   register_parser_tests();
   register_grammar_tests();
   register_misc_tests();
+  register_mm_tests();
   register_regression_tests();
   if (g_test_slow() || g_test_perf())
     register_benchmark_tests();

src/test_suite.h

@@ -321,6 +321,7 @@
 #define g_check_cmp_int64(n1, op, n2) g_check_inttype("%" PRId64, int64_t, n1, op, n2)
 #define g_check_cmp_uint32(n1, op, n2) g_check_inttype("%u", uint32_t, n1, op, n2)
 #define g_check_cmp_uint64(n1, op, n2) g_check_inttype("%" PRIu64, uint64_t, n1, op, n2)
+#define g_check_cmp_ptr(n1, op, n2) g_check_inttype("%p", void *, n1, op, n2)
 #define g_check_cmpfloat(n1, op, n2) g_check_inttype("%g", float, n1, op, n2)
 #define g_check_cmpdouble(n1, op, n2) g_check_inttype("%g", double, n1, op, n2)