fix bug

Add test for arena_attach

.clang-format

@@ -1,2 +1,10 @@
 
 BasedOnStyle: WebKit
+
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: true
+AlignConsecutiveDeclarations: true
+AlignEscapedNewlines: Left
+AlignOperands: true
+AlignTrailingComments: false
+PointerAlignment: Right

.gitignore

@@ -1,5 +1,5 @@
 obj/
-test/
 *.o
 *.a
 *.so
+build/

CMakeLists.txt

@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.16)
+
+project("ArenaAllocator"
+	VERSION 1.0
+	LANGUAGES C
+	DESCRIPTION "Arena Allocator in C"
+)
+
+add_subdirectory(src)
+
+if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
+	message(STATUS "Building tests")
+	add_subdirectory(test)
+endif()
+

Makefile

@@ -1,72 +0,0 @@
-
-all:
-
-BUILD ?= debug
-COMPILER ?= gcc
-
-# ==== set compiler flags ====
-# credits Maxim Egorushkin:
-# https://stackoverflow.com/questions/48791883/best-practice-for-building-a-make-file/48793058#48793058
-
-CC := $(COMPILER)
-
-# -fsanitize={address,undefined}
-CFLAGS.gcc.debug := -Og -ggdb -pg -fsanitize=address -fno-omit-frame-pointer
-CFLAGS.gcc.release := -O3 -g -march=native -DNDEBUG
-CFLAGS.gcc := -fanalyzer
-
-CFLAGS.clang.debug :=-O0 -g3 -DBACKTRACE -rdynamic
-CFLAGS.clang.release :=-O3 -g -march=native -DNDEBUG
-CFLAGS.clang :=
-
-CFLAGS := ${CFLAGS.${COMPILER}} ${CFLAGS.${COMPILER}.${BUILD}} \
-		  -Iinclude \
-		  -std=c2x \
-		  -Wall -Wextra -Wpedantic -Werror
-
-BUILD_DIR := build
-BIN_DIR := lib
-TEST_DIR := test
-
-OBJS := $(BUILD_DIR)/arena.o
-FPIC_OBJS := $(BUILD_DIR)/fpic/arena.o
-
-all : static
-
-static : $(BIN_DIR)/libarena.a
-
-dynamic : $(BIN_DIR)/libarena.so
-
-tests : test/test_arena
-
-$(TEST_DIR)/test_arena : src/test_arena.c $(BIN_DIR)/libarena.a | $(TEST_DIR)
-	$(CC) -o $@ $(CFLAGS) $^
-
-$(BIN_DIR)/libarena.a : $(OBJS) | $(BIN_DIR)
-	ar cr $@ $^
-
-$(BIN_DIR)/libarena.so : $(FPIC_OBJS) | $(BIN_DIR)
-	$(CC) -o $@ -shared $(CFLAGS) $^
-
-$(BUILD_DIR)/%.o : src/%.c | $(BUILD_DIR)
-	$(CC) -o $@ -c $(CFLAGS) $<
-
-$(BUILD_DIR)/fpic/%.o : src/%.c  | $(BUILD_DIR)/fpic
-	$(CC) -o $@ -c -fPIC $(CFLAGS) $<
-
-$(BUILD_DIR):
-	mkdir -p $@
-
-$(BUILD_DIR)/fpic:
-	mkdir -p $@
-
-$(BIN_DIR) :
-	mkdir -p $@
-
-$(TEST_DIR) :
-	mkdir -p $@
-
-clean:
-	rm -rf $(BUILD_DIR) $(BIN_DIR) $(TEST_DIR)
-
-.PHONY: clean $(BUILD_DIR) test bin all

README.md

@@ -1,13 +1,65 @@
 
+# Arena Allocator
+
+Arena allocators are region based allocators that tie many allocations to a
+single region of memory. Benefits are massivly simplified allocation and
+deallocation for complex structures, increased performance due to improved
+cache locality, and reduced memory fragmentation as long as individual items
+don't need to be deallocated. For programs that need to micro-manage individual
+allocations this is not an ideal solution.
+
+Deallocating a region of memory with arenas is extremely fast, because the
+arena length is just set to 0. Allocating memory is also extremely fast.  This
+implementation also grows the arena on demand using mmap and mprotect.
+Extending the library with a new type of allocation strategy should be easy.
+
+# Reference
+
 
-`arena_t* arena_new()`
+## `arena_t arena_new()`
 
-Initializes and returns new arena
+Allocate a new arena.
 
-`void arena_reset(arena_t *a)`
+If `arena_new()` fails, the struct member `data` is set to NULL.  This can be
+checked with `arena_new_failed()`
 
-Free memory allocated in arena
 
-`void* arena_alloc(arena_t *a, size_t len)`
+## `bool arena_new_failed(arena_t *a)`
+
+Returns true if creating a new arena failed
+
+
+## `int arena_delete(arena_t *a)`
+
+Delete underlying buffer of arena.  Should only be used with arenas from
+`arena_new()`.
+
+Returns 0 on success, -1 on failure
+
+
+## `arena_t arena_attach(void *ptr, size_t size)`
+
+Attach an arena to an existing memory region.  The arena will not expand if
+capacity is exceeded.
+
+
+## `void *arena_detatch(arena_t arena)`
+
+Detach an arena from an existing memory region. Returns the underlying data.
+
+
+## `void arena_reset(arena_t *a)`
+
+Resets an arena.
+
+
+## `void *arena_alloc(arena_t *a, size_t len)`
+
+Allocate memory with an arena. Returns NULL and sets errno on failure.
+
+
+## `void *arena_calloc(arena_t *a, size_t nmemb, size_t size)`
+
+Allocate and zero memory with an arena.  Returns NULL and sets errno on
+failure.
 
-Allocate new memory using arena

include/arena.h

@@ -1,24 +1,81 @@
 
+#pragma once
 #ifndef ARENA_H
 #define ARENA_H
 
-#include <stddef.h> // ptrdiff_t
+#include <stdbool.h>
-#include <stdint.h> // uintptr_t
+#include <stddef.h>
 
-#define _WORD_SIZE (sizeof(intptr_t))
+// flags = 0 should be considered the default
+enum arena_flags {
+    ARENA_GROW      = 1 << 0,
+    ARENA_DONTALIGN = 1 << 1,
+};
 
-// linked list terminology:
-// https://web.archive.org/web/20230604145332/https://i.stack.imgur.com/2FbXf.png
 typedef struct arena {
-    struct page *head, *last;
+    char*  data;
-} __attribute__((aligned(_WORD_SIZE))) arena_t;
+    size_t size;
+    size_t cap;
+    char   flags;
+} arena_t;
 
-arena_t arena_new(void);
+/**
-void arena_reset(arena_t* a);
+ * Allocate a new arena.
+ * The underlying memory is allocated with mmap.
+ * Errors can be checked with `arena_new_failed()`
+ */
+arena_t arena_new();
+
+/**
+ * Delete memory mapped for arena.
+ * Should only be used with arenas from arena_new().
+ * Returns 0 on success, -1 on failure
+ */
+int arena_delete(arena_t *a);
+
+/**
+ * Attach an arena to an existing memory region.
+ * The arena will not expand the region if space is exceeded.
+ */
+static inline arena_t arena_attach(void *ptr, size_t size)
+{
+    return (arena_t) { .data = ptr, .size = 0, .cap = size, .flags = 0 };
+}
+
+/**
+ * Detach an arena from an existing memory region.
+ */
+static inline void *arena_detatch(arena_t arena)
+{
+    return arena.data;
+}
+
+/**
+ * Returns true if creating new arena failed
+ */
+static inline bool arena_new_failed(arena_t *a)
+{
+    return a->data == NULL;
+}
+
+/**
+ * Reset an arena.
+ */
+static inline void arena_reset(arena_t *a)
+{
+    a->size = 0;
+}
+
+/**
+ * Allocate memory from an arena.
+ * Returns NULL and sets errno on failure.
+ */
 void *arena_alloc(arena_t *a, size_t len);
+
+/**
+ * Allocate and zero memory from an arena.
+ * Returns NULL and sets errno on failure.
+ */
 void *arena_calloc(arena_t *a, size_t nmemb, size_t size);
-void* arena_realloc_tail(arena_t* a, size_t len);
-void arena_delete(arena_t* a);
-void arena_free(arena_t* a, void* p);
 
 #endif

include/knob.h

@@ -0,0 +1,6 @@
+
+#pragma once
+
+#define KNOB_MMAP_SIZE (1UL << 36UL)
+#define KNOB_ALIGNMENT (sizeof(char*))
+

src/CMakeLists.txt

@@ -0,0 +1,4 @@
+
+add_library(arena arena.c)
+
+target_include_directories(arena PUBLIC ../include)

src/arena.c

@@ -1,158 +1,125 @@
 
 #include "arena.h"
+#include "knob.h"
 
-#include <errno.h>
+#include <errno.h> // errno
-#include <stdint.h>
+#include <stdbool.h>
-#include <stdlib.h>
+#include <stdio.h> // fprintf
-#include <string.h>
+#include <string.h> // strerror
+#include <sys/mman.h>
 #include <unistd.h>
 
-// (sizeof(intptr_t) isn't guaranteed to be the machine word size but on most
-// compilers it is)
-#define SYS_PAGE_SIZE ((size_t)sysconf(_SC_PAGE_SIZE))
 
-#define BIG_PAGE (SYS_PAGE_SIZE + 1)
+#ifndef NDEBUG
+#define arena_err(msg) \
+    fprintf(stderr, "%s (%s:%d): %s\n", msg, __func__, __LINE__, strerror(errno))
+#else
+#define arena_err(msg)
+#endif
 
-typedef unsigned char byte_t;
+static bool arena_grow(struct arena *a, size_t min_size)
-
-struct page {
-    void* data;
-    size_t offset, prev_offset;
-    struct page* next;
-};
-
-// linked list terminology:
-// https://web.archive.org/web/20230604145332/https://i.stack.imgur.com/2FbXf.png
-
-arena_t arena_new(void)
 {
-    struct page* p = malloc(sizeof *p);
+    if (!(a->flags & ARENA_GROW)) {
+        return false;
+    }
 
-    if (p == NULL)
+    size_t new_cap = a->cap * 2;
-        exit(errno);
+    while (new_cap < min_size) {
+        new_cap *= 2;
+    }
 
-    p->next = NULL;
+    int ok = mprotect(
-    p->offset = 0;
+        a->data + a->cap,
-    p->prev_offset = 0;
+        new_cap - a->cap,
-    p->data = malloc(SYS_PAGE_SIZE);
+        PROT_READ | PROT_WRITE
+    );
 
-    if (p->data == NULL)
+    if (ok == -1) {
-        exit(errno);
+        arena_err("mprotect");
+        return false;
+    }
 
-    arena_t a = {
+    a->cap = new_cap;
-        .head = p,
+
-        .last = p,
+    return true;
+}
+
+
+arena_t arena_new()
+{
+    size_t size = sysconf(_SC_PAGE_SIZE);
+    if (size == -1) {
+        arena_err("sysconf");
+        goto sysconf_failed;
+    }
+
+    void *p = mmap(NULL, KNOB_MMAP_SIZE, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    if (p == MAP_FAILED) {
+        arena_err("mmap");
+        goto mmap_failed;
+    }
+
+    int ok = mprotect(p, size, PROT_READ | PROT_WRITE);
+    if (ok == -1) {
+        arena_err("mprotect");
+        goto mprotect_failed;
+    }
+
+    struct arena a = {
+        .data = p,
+        .size = 0,
+        .cap = size,
+        .flags = ARENA_GROW,
     };
 
     return a;
+
+mprotect_failed:
+    ok = munmap(p, KNOB_MMAP_SIZE);
+    if (ok == -1) {
+        arena_err("munmap");
     }
-
+mmap_failed:
-void _arena_new_page(arena_t* a, size_t size)
+sysconf_failed:
-{
+    return (arena_t) { 0 };
-    /* potentially reuse page from previously
-       reset arena */
-    if (a->head->next != NULL) {
-        a->head = a->head->next;
-        a->head->offset = 0;
-        a->head->prev_offset = 0;
-        return;
-    }
-
-    void* tmp = calloc(1, sizeof *(a->head->next));
-
-    if (tmp == NULL)
-        exit(errno);
-
-    a->head->next = tmp;
-
-    a->head = a->head->next;
-    a->head->data = malloc(size);
-
-    if (a->head->data == NULL)
-        exit(errno);
-}
-
-void arena_reset(arena_t* a)
-{
-    a->head = a->last;
-    a->head->offset = 0;
-    a->head->prev_offset = 0;
-}
-
-void* _arena_big_alloc(arena_t* a, size_t size)
-{
-    _arena_new_page(a, size);
-    a->head->offset = BIG_PAGE;
-    a->head->prev_offset = BIG_PAGE;
-
-    return a->head->data;
 }
 
 void* arena_alloc(arena_t *a, size_t size)
 {
-    if (size > SYS_PAGE_SIZE)
+    // align
-        return _arena_big_alloc(a, size);
+    if (!(a->flags & ARENA_DONTALIGN)) {
-
+        size = (size + KNOB_ALIGNMENT - 1) & ~(KNOB_ALIGNMENT - 1);
-    // align size to machine word size
-    size = (size + _WORD_SIZE - 1) & ~(_WORD_SIZE - 1);
-
-    if (a->head->offset > SYS_PAGE_SIZE - size) {
-        _arena_new_page(a, SYS_PAGE_SIZE);
-        return arena_alloc(a, size);
     }
 
-    a->head->prev_offset = a->head->offset;
+    void *p = a->data + a->size;
-    a->head->offset += size;
+    if (a->size + size > a->cap) {
-
+        if (!arena_grow(a, a->size))
-    return (byte_t*)(a->head->data) + a->head->prev_offset;
+            return NULL;
+    }
+    a->size += size;
+    return p;
 }
 
 void* arena_calloc(arena_t *a, size_t nmemb, size_t size)
 {
     void *p = arena_alloc(a, nmemb * size);
+    if (p == NULL)
+        return p;
     memset(p, 0, nmemb * size);
     return p;
 }
 
-void* arena_realloc_tail(arena_t* a, size_t len)
+int arena_delete(struct arena *a)
 {
-    if (len <= (a->head->offset - a->head->prev_offset)) {
+    if (!(a->flags & ARENA_GROW)) {
-        a->head->offset = a->head->prev_offset + len;
+        return -1;
-        return (byte_t*)(a->head->data) + a->head->prev_offset;
     }
-
+    int ok = munmap(a->data, KNOB_MMAP_SIZE);
-    if (a->head->offset == BIG_PAGE) {
+    if (ok == -1) {
-        void* tmp = realloc(a->head->data, len);
+        arena_err("munmap");
-
+        return -1;
-        if (tmp == NULL)
-            exit(errno);
-
-        a->head->data = tmp;
-
-        return tmp;
     }
-
+    a->cap  = -1;
-    a->head->offset = a->head->prev_offset;
+    a->size = -1;
-
+    return 0;
-    return arena_alloc(a, len);
-}
-
-void arena_delete(arena_t* a)
-{
-    struct page* p = a->last;
-
-    while (p != NULL) {
-        struct page* next = p->next;
-        free(p->data);
-        free(p);
-        p = next;
-    }
-}
-
-// included for completeness
-void arena_free(arena_t* a, void* p)
-{
-    (void)p;
-    (void)a;
-    return;
 }

src/test_arena.c

@@ -1,42 +0,0 @@
-
-
-// _start test_arena_alloc.c
-#include "arena.h"
-
-#include <err.h>
-#include <errno.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
-
-int main()
-{
-    arena_t default_arena = arena_new();
-
-    printf("\nAttempting to allocate and write to 1 byte 1024 times");
-    for (size_t i = 0; i < 1024; i++) {
-        char* c = arena_alloc(&default_arena, sizeof *c);
-
-        if (c == NULL)
-            err(EXIT_FAILURE, "failed to allocate memory");
-
-        *c = i & 0xFF;
-    }
-    printf("\n    OK!\n");
-
-    printf("\nAttempting to allocate and write to `_SC_PAGESIZE+1` bytes");
-    size_t psz = sysconf(_SC_PAGESIZE) + 1;
-    char* c = arena_alloc(&default_arena, psz);
-
-    if (c == NULL)
-        err(EXIT_FAILURE, "failed to allocate memory");
-
-    for (size_t i = 0; i < psz; i++)
-        *c = i & 0xFF;
-
-    printf("\n    OK!\n");
-
-    arena_delete(&default_arena);
-
-    return 0;
-}

test/CMakeLists.txt

@@ -0,0 +1,6 @@
+
+include_directories(${CMAKE_SOURCE_DIR}/include)
+
+add_executable(test_arena test_arena.c)
+
+target_link_libraries(test_arena arena)

test/README

@@ -0,0 +1,6 @@
+
+run compiled test in conjunction with other tools, e.g.
+
+/usr/bin/time strace -e trace=\!write ./test/test_arena
+
+ 

test/test_arena.c

@@ -0,0 +1,153 @@
+
+#include "arena.h"
+#include "knob.h"
+
+#include <signal.h>
+#include <stdio.h>  // fprintf
+#include <stdlib.h> // exit, EXIT_FAILURE
+#include <string.h> // memset
+#include <sys/wait.h> // waitpid
+#include <unistd.h> // sysconf
+
+int main()
+{
+    size_t page_size = sysconf(_SC_PAGE_SIZE);
+    if (page_size == -1) {
+        perror("sysconf");
+        exit(EXIT_FAILURE);
+    }
+
+    /*
+     * test arena from arena_new();
+     * ===============================
+     */
+    {
+        fprintf(stderr, "creating new arena with arena_new()\n    ");
+        arena_t a = arena_new();
+        if (arena_new_failed(&a)) {
+            fprintf(stderr, "arena_new failed\n");
+            exit(EXIT_FAILURE);
+        }
+        fprintf(stderr, "OK\n");
+
+        fprintf(stderr, "attempting many small allocations\n    ");
+        for (int i = 0; i < page_size * 8; i++) {
+            char* s = arena_alloc(&a, 4 * sizeof *s);
+            if (!s) {
+                fprintf(stderr, "arena_alloc failed\n");
+                exit(EXIT_FAILURE);
+            }
+            memset(s, 'a', 4);
+        }
+        fprintf(stderr, "OK\n");
+
+        fprintf(stderr, "testing allocations of cap * 3 + 123\n    ");
+        for (int i = 0; i < 2; i++) {
+            size_t n = a.cap * 3 + 123;
+            volatile char* s = arena_alloc(&a, n);
+            if (!s) {
+                fprintf(stderr, "arena_alloc failed\n");
+                exit(EXIT_FAILURE);
+            }
+        }
+        fprintf(stderr, "OK\n");
+
+        fprintf(stderr, "calling arena_delete() on arena from arena_new()\n    ");
+        int ok = arena_delete(&a);
+        if (ok == -1) {
+            fprintf(stderr, "arena_delete failed\n");
+            exit(EXIT_FAILURE);
+        }
+        fprintf(stderr, "OK\n");
+    }
+
+    /*
+     * test arena made by arena_attach();
+     * ===============================
+     */
+    {
+        fprintf(stderr, "creating new arena with arena_attach() and malloc()\n    ");
+        char* p = malloc(page_size);
+        if (!p) {
+            perror("malloc");
+            exit(EXIT_FAILURE);
+        }
+        arena_t a = arena_attach(p, page_size);
+        fprintf(stderr, "OK\n");
+
+        bool failed = false;
+
+        fprintf(stderr, "try to grow more than the buffer size (should fail)\n    ");
+        int i;
+        for (i=0; i < page_size + 1; i++) {
+            char* s = arena_alloc(&a, 8);
+            if (!s) {
+                failed = true;
+                break;
+            }
+        }
+        if (!failed) {
+            fprintf(stderr, "allocation was supposed to fail, but didn't\n");
+            exit(EXIT_FAILURE);
+        } else if (i != page_size / KNOB_ALIGNMENT ) {
+            fprintf(stderr, "allocation failed after %d allocations, but should fail after %d!\n", i, page_size/sizeof(void*));
+            exit(EXIT_FAILURE);
+        }
+        fprintf(stderr, "OK\n");
+
+        fprintf(stderr, "deleting an arena not made with arena_new (should fail)\n    ");
+        int ok = arena_delete(&a);
+        if (ok != -1) {
+            fprintf(stderr, "arena_delete was supposed to fail, but didn't\n");
+            exit(EXIT_FAILURE);
+        }
+        fprintf(stderr, "OK\n");
+
+        free(arena_detatch(a));
+    }
+
+    /*
+     * test the memory protection
+     * ===============================
+     */
+    {
+        fprintf(stderr, "attempting to access memory beyond arena cap (should sigsegv)\n    ");
+        pid_t p;
+        switch (p = fork()) {
+        case -1: /* error */
+            perror("fork()");
+            exit(EXIT_FAILURE);
+
+        case 0: /* child */
+            arena_t a = arena_new();
+            if (arena_new_failed(&a)) {
+                fprintf(stderr, "arena_new failed\n");
+                exit(EXIT_FAILURE);
+            }
+
+            char* s = arena_alloc(&a, 12345);
+            if (!s) {
+                fprintf(stderr, "arena_alloc failed\n");
+                exit(EXIT_FAILURE);
+            }
+
+            // should sigsegv
+            a.data[a.cap] = 1;
+            exit(EXIT_SUCCESS);
+        }
+
+        int status;
+        int ok = waitpid(p, &status, 0);
+        if (!ok) {
+            perror("waitpid");
+        }
+
+        if (!( WIFSIGNALED(status) && WTERMSIG(status) == SIGSEGV)) {
+            fprintf(stderr, "allocating beyond arena cap succeeded when it shouldn't!\n");
+            exit(EXIT_FAILURE);
+        }
+        fprintf(stderr, "OK\n");
+    }
+
+    return EXIT_SUCCESS;
+}