fix bug

Add test for arena_attach

.clang-format

@@ -0,0 +1,10 @@
+
+BasedOnStyle: WebKit
+
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: true
+AlignConsecutiveDeclarations: true
+AlignEscapedNewlines: Left
+AlignOperands: true
+AlignTrailingComments: false
+PointerAlignment: Right

.gitignore

@@ -0,0 +1,5 @@
+obj/
+*.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

@@ -1,27 +0,0 @@
-
-CC := gcc
-CFLAGS := -ggdb -O0 -std=c99 -Wall -Wextra -Wpedantic
-
-OBJS := obj/arena.o obj/alloc_backend.o
-
-all : test/test_arena
-
-test/test_arena : src/test_arena.c $(OBJS) | test
-	$(CC) -o $@ $(CFLAGS) $^
-
-obj/%.o : src/%.c | obj
-	$(CC) -o $@ -c $(CFLAGS) $<
-
-obj:
-	mkdir -p $@
-
-bin:
-	mkdir -p $@
-
-test:
-	mkdir -p $@
-
-clean:
-	rm -rf obj bin test
-
-.PHONY: clean obj test bin all

README.md

@@ -0,0 +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()`
+
+Allocate a new arena.
+
+If `arena_new()` fails, the struct member `data` is set to NULL.  This can be
+checked with `arena_new_failed()`
+
+
+## `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.
+

compile_flags.txt

@@ -0,0 +1,5 @@
+-Wall
+-Wextra
+-Wpedantic
+-std=c2x
+-Iinclude

include/arena.h

@@ -0,0 +1,81 @@
+
+#pragma once
+#ifndef ARENA_H
+#define ARENA_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+// flags = 0 should be considered the default
+enum arena_flags {
+    ARENA_GROW      = 1 << 0,
+    ARENA_DONTALIGN = 1 << 1,
+};
+
+typedef struct arena {
+    char*  data;
+    size_t size;
+    size_t cap;
+    char   flags;
+} arena_t;
+
+/**
+ * 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);
+
+#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/alloc_backend.c

@@ -1,30 +0,0 @@
-
-#include "alloc_backend.h"
-
-#define _GNU_SOURCE
-#include <sys/mman.h>
-
-/*
- * Separate function to make switching
- * allocation backend easier
- *
- * must take size_t size as an argument
- * must return NULL on failure
- */
-void* call_alloc_backend(size_t size)
-{
-    void *p = mmap(
-            NULL,
-            size,
-            PROT_READ | PROT_WRITE, 
-            MAP_ANONYMOUS | MAP_PRIVATE,
-            -1, /* man mmap(2): "[...], some implementations require fd to be
-                   -1 if MAP_ANONYMOUS is specified [...]" */
-            0
-    );
-
-    if (p == MAP_FAILED)
-        return NULL;
-
-    return p;
-}

src/alloc_backend.h

@@ -1,9 +0,0 @@
-
-#ifndef ALLOC_BACKEND_H
-#define ALLOC_BACKEND_H
-
-#include <stddef.h>
-
-void* call_alloc_backend(size_t size);
-
-#endif

src/arena.c

@@ -1,60 +1,125 @@
 
-
 #include "arena.h"
-#include "alloc_backend.h"
+#include "knob.h"
 
-#include <errno.h>
+#include <errno.h> // errno
+#include <stdbool.h>
+#include <stdio.h> // fprintf
+#include <string.h> // strerror
+#include <sys/mman.h>
 #include <unistd.h>
-#include <string.h>
 
-#define ARENA_SIZE ((size_t)(128*sysconf(_SC_PAGE_SIZE)))
 
-/*
+#ifndef NDEBUG
- * Allocates and returns new arena
+#define arena_err(msg) \
- */
+    fprintf(stderr, "%s (%s:%d): %s\n", msg, __func__, __LINE__, strerror(errno))
-struct arena* arena_new()
+#else
+#define arena_err(msg)
+#endif
+
+static bool arena_grow(struct arena *a, size_t min_size)
 {
-    size_t size = ARENA_SIZE;
+    if (!(a->flags & ARENA_GROW)) {
-
+        return false;
-    unsigned char *p = call_alloc_backend(size);
-
-    if (p == NULL)
-        return NULL;
-
-    struct arena a = {
-        .begin = p + sizeof(struct arena),
-        .next  = p + sizeof(struct arena),
-        .cap   = size
-    };
-
-    memcpy(p, &a, sizeof a);
-
-    return (struct arena*)p;
-}
-
-
-/*
- * Frees all memory in arena
- */
-void arena_reset(struct arena *a)
-{
-    a->next = a->begin;
-}
-
-
-/*
- * Allocate new memory using arena
- */
-void* arena_alloc(struct arena *a, size_t len)
-{
-    void *p = a->next;
-    a->next += len;
-
-    if (a->next - a->begin >= a->cap) {
-        errno = ENOMEM;
-        return NULL;
     }
 
+    size_t new_cap = a->cap * 2;
+    while (new_cap < min_size) {
+        new_cap *= 2;
+    }
+
+    int ok = mprotect(
+        a->data + a->cap,
+        new_cap - a->cap,
+        PROT_READ | PROT_WRITE
+    );
+
+    if (ok == -1) {
+        arena_err("mprotect");
+        return false;
+    }
+
+    a->cap = new_cap;
+
+    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:
+sysconf_failed:
+    return (arena_t) { 0 };
+}
+
+void* arena_alloc(arena_t *a, size_t size)
+{
+    // align
+    if (!(a->flags & ARENA_DONTALIGN)) {
+        size = (size + KNOB_ALIGNMENT - 1) & ~(KNOB_ALIGNMENT - 1);
+    }
+
+    void *p = a->data + a->size;
+    if (a->size + size > a->cap) {
+        if (!arena_grow(a, a->size))
+            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;
+}
+
+int arena_delete(struct arena *a)
+{
+    if (!(a->flags & ARENA_GROW)) {
+        return -1;
+    }
+    int ok = munmap(a->data, KNOB_MMAP_SIZE);
+    if (ok == -1) {
+        arena_err("munmap");
+        return -1;
+    }
+    a->cap  = -1;
+    a->size = -1;
+    return 0;
+}

src/arena.h

@@ -1,19 +0,0 @@
-
-#ifndef ARENA_H
-#define ARENA_H
-
-
-#include <stddef.h> // ptrdiff_t
-
-struct arena {
-    unsigned char *begin,
-                  *next;
-    ptrdiff_t cap;
-};
-
-struct arena* arena_new();
-void arena_reset(struct arena *a);
-void* arena_alloc(struct arena *a, size_t len);
-
-
-#endif

src/test_arena.c

@@ -1,44 +0,0 @@
-
-
-
-// _start test_arena_alloc.c
-#include "arena.h"
-#include <err.h>
-#include <stdio.h>
-#include <errno.h>
-
-static struct arena *default_arena = NULL;
-
-int main()
-{
-    default_arena = arena_new();
-
-    if (default_arena == NULL) {
-        err(errno, "failed to allocate arena");
-    }
-
-	printf("\n%p\n", default_arena->next);
-
-    char *ten_A = arena_alloc(default_arena, 11 * sizeof *ten_A);
-    char *ten_B = arena_alloc(default_arena, 11 * sizeof *ten_B);
-    char *ten_C = arena_alloc(default_arena, 11 * sizeof *ten_C);
-
-    for (size_t i=0; i<10; ++i) {
-        ten_A[i] = 'A';
-        ten_B[i] = 'B';
-        ten_C[i] = 'C';
-    }
-
-    ten_A[10] = '\0';
-    ten_B[10] = '\0';
-    ten_C[10] = '\0';
-
-    printf("\n%s %s %s", ten_A, ten_B, ten_C);
-	printf("\n%p\n", default_arena->next);
-
-	arena_reset(default_arena);
-
-	printf("\n%p\n", default_arena->next);
-
-    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;
+}