Reimplement the arena

example/arena.c

@@ -9,13 +9,13 @@ typedef struct {
 
 int main(void)
 {
-    Arena *arena = arena_make(sizeof(int));
-    defer { arena_destroy(arena); }
+    Arena arena = gebs_arena_get(4*1024);
+    defer { arena_destroy(&arena); }
 
     Ints ints = {0};
-    defer { list_free_alloc(arena, &ints); }
-    for (size_t i = 0; i < 1000; i++) {
-        list_append_alloc(arena, &ints, i);
+    for (size_t i = 0; i < 100; i++) {
+        list_append_alloc(&arena, &ints, i);
+        gebs_arena_reset(&arena);
     }
     for (size_t i = 0; i < ints.count; i++) {
         printf("%zu\n", i);

gebs.h

@@ -33,6 +33,7 @@
 #   include <sys/stat.h>
 #   include <sys/types.h>
 #   include <sys/wait.h>
+#   include <sys/mman.h>
 #else
 #   error "Unknown GEBS_PLATFORM"
 #endif
@@ -96,31 +97,32 @@ void gebs_default_allocator_free(void *self, void *memory);
 void *gebs_default_allocator_realloc(void *self, void *memory,
                                      size_t prev_size, size_t new_size);
 
-typedef struct Gebs_Arena_Allocation {
-    size_t index;
-    size_t size;
-    char *ptr;
-    struct Gebs_Arena_Allocation *next;
-} Gebs_Arena_Allocation;
-
 typedef struct {
     void *(*malloc)(void *self, size_t size);
     void (*free)(void *self, void *memory);
     void *(*realloc)(void *self, void *memory, size_t prev_size, size_t new_size);
 
-    char *region;
-    size_t index;
-    size_t size;
+    void *buffer;
+    void *end;
+    size_t capacity;
 } Gebs_Arena;
 
 void gebs_arena_reset(Gebs_Arena *a);
 void gebs_arena_destroy(Gebs_Arena *a);
-Gebs_Arena *gebs_arena_make(size_t size);
-Gebs_Arena *gebs_arena_expand(Gebs_Arena *a, size_t new_size);
 void *gebs_arena_malloc(void *self, size_t size);
 void gebs_arena_free(void *self, void *memory);
 void *gebs_arena_realloc(void *self, void *memory, size_t prev_size, size_t new_size);
 
+#define gebs_arena_get(cap) \
+({ \
+    Gebs_Arena __arena = {0}; \
+    __arena.malloc = &gebs_arena_malloc; \
+    __arena.realloc = &gebs_arena_realloc; \
+    __arena.free = &gebs_arena_free; \
+    __arena.capacity = (cap); \
+    __arena; \
+})
+
 // ----------------------------------------------------------------------------
 // Dynamic list
 // ----------------------------------------------------------------------------
@@ -301,7 +303,7 @@ void gebs_rebuild_self1_alloc(Gebs_Allocator *alloc, int argc, char ** argv,
 #   define GEBS_SCRATCH_ARENA_SIZE 4096
 #endif
 
-extern Gebs_Arena *gebs_scratch_arena;
+extern Gebs_Arena gebs_scratch_arena;
 
 char *gebs_fmt(const char *fmt, ...);
 void gebs_scratch_arena_reset(void);
@@ -316,6 +318,7 @@ int gebs_cmd_run_sync_alloc(Gebs_Allocator *alloc, Gebs_Cmd *cmd)
 {
     Gebs_String_Builder sb = {0};
     gebs_nsl_join_alloc(alloc, cmd, &sb, " ");
+    gebs_sb_finish_alloc(alloc, &sb);
     GEBS_LOGI("cmd `%s`\n", sb.items);
 
 #if GEBS_PLATFORM == GEBS_PLATFORM_POSIX
@@ -363,6 +366,7 @@ int gebs_cmd_run_sync_collect_alloc(Gebs_Allocator *alloc, Gebs_Cmd *cmd, Gebs_S
 {
     Gebs_String_Builder sb = {0};
     gebs_nsl_join_alloc(alloc, cmd, &sb, " ");
+    gebs_sb_finish_alloc(alloc, &sb);
     GEBS_LOGI("cmd `%s`\n", sb.items);
 
 #if GEBS_PLATFORM == GEBS_PLATFORM_POSIX
@@ -449,68 +453,23 @@ void *gebs_default_allocator_realloc(discard void *self, void *memory,
     return p;
 }
 
-Gebs_Arena *gebs_arena_make(size_t size)
-{
-    Gebs_Arena *a;
-    if (size == 0) {
-        return NULL;
-    }
-
-    a = malloc(sizeof(*a));
-    if (a == NULL) {
-        return NULL;
-    }
-
-    a->malloc = &gebs_arena_malloc;
-    a->free = &gebs_arena_free;
-    a->realloc = &gebs_arena_realloc;
-
-    a->region = malloc(size);
-    if (a->region == NULL) {
-        free(a);
-        return NULL;
-    }
-
-    a->index = 0;
-    a->size = size;
-    return a;
-}
-
-Gebs_Arena *gebs_arena_expand(Gebs_Arena *a, size_t new_size)
-{
-    if (a == NULL || new_size <= a->size) {
-        return NULL;
-    }
-
-    a->region = realloc(a->region, new_size);
-    if (a->region == NULL) {
-        return NULL;
-    }
-
-    a->size = new_size;
-    return a;
-}
-
 void *gebs_arena_malloc(void *self, size_t size)
 {
     Gebs_Arena *a = (Gebs_Arena *)self;
-    unsigned int offset;
 
-    if (size == 0) {
-        return NULL;
+    if (a->buffer == NULL) {
+#if GEBS_PLATFORM == GEBS_PLATFORM_POSIX
+        int prot = PROT_READ | PROT_WRITE;
+        int vis = MAP_SHARED | MAP_ANONYMOUS;
+        a->buffer = mmap(0, a->capacity, prot, vis, -1, 0);
+#else
+#   error "gebs_arena_malloc unknown platform"
+#endif
+        a->end = a->buffer;
     }
-
-    if (a == NULL || a->region == NULL) {
-        return NULL;
-    }
-
-    offset = 0;
-    if (a->size - (a->index + offset) < size) {
-        return NULL;
-    }
-
-    a->index += size;
-    return a->region + (a->index - size);
+    void *p = a->end;
+    a->end = (void *)((uintptr_t)a->end + size);
+    return p;
 }
 
 void gebs_arena_free(discard void *self, discard void *memory)
@@ -518,53 +477,45 @@ void gebs_arena_free(discard void *self, discard void *memory)
 }
 
 void *gebs_arena_realloc(void *self, void *memory,
-                         discard size_t prev_size, size_t new_size)
+                         size_t prev_size, size_t new_size)
 {
     Gebs_Arena *a = (Gebs_Arena *)self;
 
-    uintptr_t offset = (char *)memory - a->region;
-    gebs_arena_expand(a, a->size + new_size);
-    return a->region + offset;
+    void *new = gebs_arena_malloc(a, new_size);
+    memcpy(new, memory, prev_size);
+    return new;
 }
 
 void gebs_arena_reset(Gebs_Arena *a)
 {
-    if (a == NULL) {
-        return;
-    }
-
-    a->index = 0;
+    a->end = a->buffer;
 }
 
 void gebs_arena_destroy(Gebs_Arena *a)
 {
-    if (a == NULL) {
-        return;
-    }
-
-    if (a->region != NULL) {
-        free(a->region);
-    }
-
-    free(a);
+#if GEBS_PLATFORM == GEBS_PLATFORM_POSIX
+    munmap(a->buffer, a->capacity);
+#else
+#   error "gebs_arena_destroy unknown platform"
+#endif
 }
 
 // ----------------------------------------------------------------------------
 // Scratch arena
 // ----------------------------------------------------------------------------
 
-Gebs_Arena *gebs_scratch_arena;
+Gebs_Arena gebs_scratch_arena;
 
 __attribute__((constructor))
 void gebs_scratch_areana_init(void)
 {
-    gebs_scratch_arena = gebs_arena_make(GEBS_SCRATCH_ARENA_SIZE);
+    gebs_scratch_arena = gebs_arena_get(4*1024);
 }
 
 __attribute__((destructor))
 void gebs_scratch_areana_free(void)
 {
-    gebs_arena_destroy(gebs_scratch_arena);
+    gebs_arena_destroy(&gebs_scratch_arena);
 }
 
 char *gebs_fmt(const char *fmt, ...)
@@ -577,7 +528,7 @@ char *gebs_fmt(const char *fmt, ...)
     size_t size = vsnprintf(NULL, 0, fmt, list_copy);
     va_end(list_copy);
 
-    char *buf = gebs_malloc(gebs_scratch_arena, size+1);
+    char *buf = gebs_malloc(&gebs_scratch_arena, size+1);
     vsprintf(buf, fmt, list);
     va_end(list);
     return buf;
@@ -585,7 +536,7 @@ char *gebs_fmt(const char *fmt, ...)
 
 void gebs_scratch_arena_reset(void)
 {
-    gebs_arena_reset(gebs_scratch_arena);
+    gebs_arena_reset(&gebs_scratch_arena);
 }
 
 // ----------------------------------------------------------------------------