Implement git_pool paged memory allocator

This adds a `git_pool` object that can do simple paged memory
allocation with free for the entire pool at once.  Using this,
you can replace many small allocations with large blocks that
can then cheaply be doled out in small pieces.  This is best
used when you plan to free the small blocks all at once - for
example, if they represent the parsed state from a file or data
stream that are either all kept or all discarded.

There are two real patterns of usage for `git_pools`: either
for "string" allocation, where the item size is a single byte
and you end up just packing the allocations in together, or for
"fixed size" allocation where you are allocating a large object
(e.g. a `git_oid`) and you generally just allocation single
objects that can be tightly packed.  Of course, you can use it
for other things, but those two cases are the easiest.

src/blob.c

@@ -139,12 +139,12 @@ static int write_symlink(
 	read_len = p_readlink(path, link_data, link_size);
 	if (read_len != (ssize_t)link_size) {
 		giterr_set(GITERR_OS, "Failed to create blob.  Can't read symlink '%s'", path);
-		free(link_data);
+		git__free(link_data);
 		return -1;
 	}
 
 	error = git_odb_write(oid, odb, (void *)link_data, link_size, GIT_OBJ_BLOB);
-	free(link_data);
+	git__free(link_data);
 	return error;
 }
 

src/buffer.c

@@ -159,7 +159,7 @@ int git_buf_printf(git_buf *buf, const char *format, ...)
 		va_end(arglist);
 
 		if (len < 0) {
-			free(buf->ptr);
+			git__free(buf->ptr);
 			buf->ptr = &git_buf__oom;
 			return -1;
 		}

src/config_file.c

@@ -370,7 +370,7 @@ static int config_set_multivar(git_config_file *cfg, const char *name, const cha
 
 	result = regcomp(&preg, regexp, REG_EXTENDED);
 	if (result < 0) {
-		free(key);
+		git__free(key);
 		giterr_set_regex(&preg, result);
 		return -1;
 	}
@@ -380,7 +380,7 @@ static int config_set_multivar(git_config_file *cfg, const char *name, const cha
 			char *tmp = git__strdup(value);
 			GITERR_CHECK_ALLOC(tmp);
 
-			free(var->value);
+			git__free(var->value);
 			var->value = tmp;
 			replaced = 1;
 		}
@@ -409,7 +409,7 @@ static int config_set_multivar(git_config_file *cfg, const char *name, const cha
 
 	result = config_write(b, key, &preg, value);
 
-	free(key);
+	git__free(key);
 	regfree(&preg);
 
 	return result;
@@ -426,7 +426,7 @@ static int config_delete(git_config_file *cfg, const char *name)
 		return -1;
 
 	var = git_hashtable_lookup(b->values, key);
-	free(key);
+	git__free(key);
 
 	if (var == NULL)
 		return GIT_ENOTFOUND;
@@ -1275,7 +1275,7 @@ static int parse_variable(diskfile_backend *cfg, char **var_name, char **var_val
 			char *proc_line = fixup_line(value_start, 0);
 			GITERR_CHECK_ALLOC(proc_line);
 			git_buf_puts(&multi_value, proc_line);
-			free(proc_line);
+			git__free(proc_line);
 			if (parse_multiline_variable(cfg, &multi_value, quote_count) < 0 || git_buf_oom(&multi_value)) {
 				git__free(*var_name);
 				git__free(line);

src/errors.c

@@ -173,7 +173,7 @@ void giterr_set_str(int error_class, const char *string)
 {
 	git_error *error = &GIT_GLOBAL->error_t;
 
-	free(error->message);
+	git__free(error->message);
 
 	error->message = git__strdup(string);
 	error->klass = error_class;

src/filter.c

@@ -111,7 +111,7 @@ void git_filters_free(git_vector *filters)
 		if (filter->do_free != NULL)
 			filter->do_free(filter);
 		else
-			free(filter);
+			git__free(filter);
 	}
 
 	git_vector_free(filters);

src/global.c

@@ -62,7 +62,7 @@ git_global_st *git__global_state(void)
 	if ((ptr = TlsGetValue(_tls_index)) != NULL)
 		return ptr;
 
-	ptr = malloc(sizeof(git_global_st));
+	ptr = git__malloc(sizeof(git_global_st));
 	if (!ptr)
 		return NULL;
 
@@ -78,7 +78,7 @@ static int _tls_init = 0;
 
 static void cb__free_status(void *st)
 {
-	free(st);
+	git__free(st);
 }
 
 void git_threads_init(void)
@@ -103,7 +103,7 @@ git_global_st *git__global_state(void)
 	if ((ptr = pthread_getspecific(_tls_key)) != NULL)
 		return ptr;
 
-	ptr = malloc(sizeof(git_global_st));
+	ptr = git__malloc(sizeof(git_global_st));
 	if (!ptr)
 		return NULL;
 

src/odb.c

@@ -169,7 +169,7 @@ int git_odb__hashlink(git_oid *out, const char *path)
 		}
 
 		result = git_odb_hash(out, link_data, (size_t)size, GIT_OBJ_BLOB);
-		free(link_data);
+		git__free(link_data);
 	} else { 
 		int fd = git_futils_open_ro(path);
 		if (fd < 0)

src/pool.c

+#include "pool.h"
+#ifndef GIT_WIN32
+#include <unistd.h>
+#endif
+
+struct git_pool_page {
+	git_pool_page *next;
+	uint32_t size;
+	uint32_t avail;
+	char data[GIT_FLEX_ARRAY];
+};
+
+#define GIT_POOL_MIN_USABLE	4
+#define GIT_POOL_MIN_PAGESZ	2 * sizeof(void*)
+
+static int pool_alloc_page(git_pool *pool, uint32_t size, void **ptr);
+static void pool_insert_page(git_pool *pool, git_pool_page *page);
+
+int git_pool_init(
+	git_pool *pool, uint32_t item_size, uint32_t items_per_page)
+{
+	assert(pool);
+
+	if (!item_size)
+		item_size = 1;
+	/* round up item_size for decent object alignment */
+	if (item_size > 4)
+		item_size = (item_size + 7) & ~7;
+	else if (item_size == 3)
+		item_size = 4;
+
+	if (!items_per_page) {
+		uint32_t page_bytes =
+			git_pool__system_page_size() - sizeof(git_pool_page);
+		items_per_page = page_bytes / item_size;
+	}
+	if (item_size * items_per_page < GIT_POOL_MIN_PAGESZ)
+		items_per_page = (GIT_POOL_MIN_PAGESZ + item_size - 1) / item_size;
+
+	memset(pool, 0, sizeof(git_pool));
+	pool->item_size = item_size;
+	pool->page_size = item_size * items_per_page;
+
+	return 0;
+}
+
+void git_pool_clear(git_pool *pool)
+{
+	git_pool_page *scan, *next;
+
+	for (scan = pool->open; scan != NULL; scan = next) {
+		next = scan->next;
+		git__free(scan);
+	}
+	pool->open = NULL;
+
+	for (scan = pool->full; scan != NULL; scan = next) {
+		next = scan->next;
+		git__free(scan);
+	}
+	pool->full = NULL;
+
+	pool->free_list = NULL;
+
+	pool->has_string_alloc     = 0;
+	pool->has_multi_item_alloc = 0;
+	pool->has_large_page_alloc = 0;
+}
+
+static void pool_insert_page(git_pool *pool, git_pool_page *page)
+{
+	git_pool_page *scan;
+
+	/* If there are no open pages or this page has the most open space,
+	 * insert it at the beginning of the list.  This is the common case.
+	 */
+	if (pool->open == NULL || pool->open->avail < page->avail) {
+		page->next = pool->open;
+		pool->open = page;
+		return;
+	}
+
+	/* Otherwise insert into sorted position. */
+	for (scan = pool->open;
+		 scan->next && scan->next->avail > page->avail;
+		 scan = scan->next);
+	page->next = scan->next;
+	scan->next = page;
+}
+
+static int pool_alloc_page(
+	git_pool *pool, uint32_t size, void **ptr)
+{
+	git_pool_page *page;
+	uint32_t alloc_size;
+
+	if (size <= pool->page_size)
+		alloc_size = pool->page_size;
+	else {
+		alloc_size = size;
+		pool->has_large_page_alloc = 1;
+	}
+
+	page = git__calloc(1, alloc_size + sizeof(git_pool_page));
+	if (!page)
+		return -1;
+
+	page->size  = alloc_size;
+	page->avail = alloc_size - size;
+
+	if (page->avail > 0)
+		pool_insert_page(pool, page);
+	else {
+		page->next = pool->full;
+		pool->full = page;
+	}
+
+	*ptr = page->data;
+
+	return 0;
+}
+
+GIT_INLINE(void) pool_remove_page(
+	git_pool *pool, git_pool_page *page, git_pool_page *prev)
+{
+	if (prev == NULL)
+		pool->open = page->next;
+	else
+		prev->next = page->next;
+}
+
+int git_pool_malloc(git_pool *pool, uint32_t items, void **ptr)
+{
+	git_pool_page *scan = pool->open, *prev;
+	uint32_t size = items * pool->item_size;
+
+	pool->has_string_alloc = 0;
+	if (items > 1)
+		pool->has_multi_item_alloc = 1;
+	else if (pool->free_list != NULL) {
+		*ptr = pool->free_list;
+		pool->free_list = *((void **)pool->free_list);
+	}
+
+	/* just add a block if there is no open one to accomodate this */
+	if (size >= pool->page_size || !scan || scan->avail < size)
+		return pool_alloc_page(pool, size, ptr);
+
+	/* find smallest block in free list with space */
+	for (scan = pool->open, prev = NULL;
+		 scan->next && scan->next->avail >= size;
+		 prev = scan, scan = scan->next);
+
+	/* allocate space from the block */
+	*ptr = &scan->data[scan->size - scan->avail];
+	scan->avail -= size;
+
+	/* move to full list if there is almost no space left */
+	if (scan->avail < pool->item_size || scan->avail < GIT_POOL_MIN_USABLE) {
+		pool_remove_page(pool, scan, prev);
+		scan->next = pool->full;
+		pool->full = scan;
+	}
+	/* reorder list if block is now smaller than the one after it */
+	else if (scan->next != NULL && scan->next->avail > scan->avail) {
+		pool_remove_page(pool, scan, prev);
+		pool_insert_page(pool, scan);
+	}
+
+	return 0;
+}
+
+char *git_pool_strndup(git_pool *pool, const char *str, size_t n)
+{
+	void *ptr = NULL;
+
+	assert(pool && str && pool->item_size == sizeof(char));
+
+	if (!git_pool_malloc(pool, n, &ptr))
+		memcpy(ptr, str, n);
+	pool->has_string_alloc = 1;
+
+	return ptr;
+}
+
+char *git_pool_strdup(git_pool *pool, const char *str)
+{
+	assert(pool && str && pool->item_size == sizeof(char));
+
+	return git_pool_strndup(pool, str, strlen(str) + 1);
+}
+
+void git_pool_free(git_pool *pool, void *ptr)
+{
+	assert(pool && ptr && pool->item_size >= sizeof(void*));
+
+	*((void **)ptr) = pool->free_list;
+	pool->free_list = ptr;
+}
+
+uint32_t git_pool__open_pages(git_pool *pool)
+{
+	uint32_t ct = 0;
+	git_pool_page *scan;
+	for (scan = pool->open; scan != NULL; scan = scan->next) ct++;
+	return ct;
+}
+
+uint32_t git_pool__full_pages(git_pool *pool)
+{
+	uint32_t ct = 0;
+	git_pool_page *scan;
+	for (scan = pool->full; scan != NULL; scan = scan->next) ct++;
+	return ct;
+}
+
+bool git_pool__ptr_in_pool(git_pool *pool, void *ptr)
+{
+	git_pool_page *scan;
+	for (scan = pool->open; scan != NULL; scan = scan->next)
+		if ( ((void *)scan->data) <= ptr &&
+			(((void *)scan->data) + scan->size) > ptr)
+			return true;
+	for (scan = pool->full; scan != NULL; scan = scan->next)
+		if ( ((void *)scan->data) <= ptr &&
+			(((void *)scan->data) + scan->size) > ptr)
+			return true;
+	return false;
+}
+
+uint32_t git_pool__system_page_size(void)
+{
+	static uint32_t size = 0;
+
+	if (!size) {
+#ifdef GIT_WIN32
+		SYSTEM_INFO info;
+		GetSystemInfo(&info);
+		size = (uint32_t)info.dwPageSize;
+#else
+		size = (uint32_t)sysconf(_SC_PAGE_SIZE);
+#endif
+
+		size -= 2 * sizeof(void *); /* allow space for malloc overhead */
+	}
+
+	return size;
+}
+

src/pool.h

+/*
+ * Copyright (C) 2012 the libgit2 contributors
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_pool_h__
+#define INCLUDE_pool_h__
+
+#include "common.h"
+
+typedef struct git_pool_page git_pool_page;
+
+/**
+ * Chunked allocator.
+ *
+ * A `git_pool` can be used when you want to cheaply allocate
+ * multiple items of the same type and are willing to free them
+ * all together with a single call.  The two most common cases
+ * are a set of fixed size items (such as lots of OIDs) or a
+ * bunch of strings.
+ *
+ * Internally, a `git_pool` allocates pages of memory and then
+ * deals out blocks from the trailing unused portion of each page.
+ * The pages guarantee that the number of actual allocations done
+ * will be much smaller than the number of items needed.
+ *
+ * For examples of how to set up a `git_pool` see `git_pool_init`.
+ */
+typedef struct {
+	git_pool_page *open; /* pages with space left */
+	git_pool_page *full; /* pages with no space left */
+	void *free_list;     /* optional: list of freed blocks */
+	uint32_t item_size;  /* size of single alloc unit in bytes */
+	uint32_t page_size;  /* size of page in bytes */
+	unsigned has_string_alloc : 1; /* was the strdup function used */
+	unsigned has_multi_item_alloc : 1; /* was items ever > 1 in malloc */
+	unsigned has_large_page_alloc : 1; /* are any pages > page_size */
+} git_pool;
+
+/**
+ * Initialize a pool.
+ *
+ * To allocation strings, use like this:
+ *
+ *     git_pool_init(&string_pool, 1, 0);
+ *     my_string = git_pool_strdup(&string_pool, your_string);
+ *
+ * To allocate items of fixed size, use like this:
+ *
+ *     git_pool_init(&pool, sizeof(item), 0);
+ *     git_pool_malloc(&pool, 1, &my_item_ptr);
+ *
+ * Of course, you can use this in other ways, but those are the
+ * two most common patterns.
+ */
+extern int git_pool_init(
+	git_pool *pool, uint32_t item_size, uint32_t items_per_page);
+
+/**
+ * Free all items in pool
+ */
+extern void git_pool_clear(git_pool *pool);
+
+/**
+ * Allocate space for one or more items from a pool.
+ */
+extern int git_pool_malloc(git_pool *pool, uint32_t items, void **ptr);
+
+/**
+ * Allocate space and duplicate string data into it.
+ *
+ * This is allowed only for pools with item_size == sizeof(char)
+ */
+extern char *git_pool_strndup(git_pool *pool, const char *str, size_t n);
+
+/**
+ * Allocate space and duplicate a string into it.
+ *
+ * This is allowed only for pools with item_size == sizeof(char)
+ */
+extern char *git_pool_strdup(git_pool *pool, const char *str);
+
+/**
+ * Push a block back onto the free list for the pool.
+ *
+ * This is allowed only if the item_size is >= sizeof(void*).
+ *
+ * In some cases, it is helpful to "release" an allocated block
+ * for reuse.  Pools don't support a general purpose free, but
+ * they will keep a simple free blocks linked list provided the
+ * native block size is large enough to hold a void pointer
+ */
+extern void git_pool_free(git_pool *pool, void *ptr);
+
+/*
+ * Misc utilities
+ */
+
+extern uint32_t git_pool__open_pages(git_pool *pool);
+
+extern uint32_t git_pool__full_pages(git_pool *pool);
+
+extern bool git_pool__ptr_in_pool(git_pool *pool, void *ptr);
+
+extern uint32_t git_pool__system_page_size(void);
+
+#endif

src/refs.c

@@ -268,7 +268,7 @@ static int loose_lookup_to_packfile(
 
 	if (loose_parse_oid(&ref->oid, &ref_file) < 0) {
 		git_buf_free(&ref_file);
-		free(ref);
+		git__free(ref);
 		return -1;
 	}
 

src/remote.c

@@ -436,7 +436,7 @@ int git_remote_list(git_strarray *remotes_list, git_repository *repo)
 		size_t i;
 		char *elem;
 		git_vector_foreach(&list, i, elem) {
-			free(elem);
+			git__free(elem);
 		}
 
 		git_vector_free(&list);

src/repository.c

@@ -850,7 +850,7 @@ int git_repository_set_workdir(git_repository *repo, const char *workdir)
 	if (git_path_prettify_dir(&path, workdir, NULL) < 0)
 		return -1;
 
-	free(repo->workdir);
+	git__free(repo->workdir);
 
 	repo->workdir = git_buf_detach(&path);
 	repo->is_bare = 0;

tests-clar/core/pool.c

+#include "clar_libgit2.h"
+#include "pool.h"
+#include "git2/oid.h"
+
+void test_core_pool__0(void)
+{
+	int i;
+	git_pool p;
+	void *ptr;
+
+	cl_git_pass(git_pool_init(&p, 1, 4000));
+
+	for (i = 1; i < 10000; i *= 2) {
+		cl_git_pass(git_pool_malloc(&p, i, &ptr));
+		cl_assert(ptr != NULL);
+
+		cl_assert(git_pool__ptr_in_pool(&p, ptr));
+		cl_assert(!git_pool__ptr_in_pool(&p, &i));
+	}
+
+	/* 1+2+4+8+16+32+64+128+256+512+1024 -> original block */
+	/* 2048 -> 1 block */
+	/* 4096 -> 1 block */
+	/* 8192 -> 1 block */
+
+	cl_assert(git_pool__open_pages(&p) + git_pool__full_pages(&p) == 4);
+
+	git_pool_clear(&p);
+}
+
+void test_core_pool__1(void)
+{
+	int i;
+	git_pool p;
+	void *ptr;
+
+	cl_git_pass(git_pool_init(&p, 1, 4000));
+
+	for (i = 2010; i > 0; i--)
+		cl_git_pass(git_pool_malloc(&p, i, &ptr));
+
+	/* with fixed page size, allocation must end up with these values */
+	cl_assert(git_pool__open_pages(&p) == 1);
+	cl_assert(git_pool__full_pages(&p) == 505);
+
+	git_pool_clear(&p);
+
+	cl_git_pass(git_pool_init(&p, 1, 4100));
+
+	for (i = 2010; i > 0; i--)
+		cl_git_pass(git_pool_malloc(&p, i, &ptr));
+
+	/* with fixed page size, allocation must end up with these values */
+	cl_assert(git_pool__open_pages(&p) == 1);
+	cl_assert(git_pool__full_pages(&p) == 492);
+
+	git_pool_clear(&p);
+}
+
+static char to_hex[] = "0123456789abcdef";
+
+void test_core_pool__2(void)
+{
+	git_pool p;
+	char oid_hex[GIT_OID_HEXSZ];
+	git_oid *oid;
+	int i, j;
+
+	memset(oid_hex, '0', sizeof(oid_hex));
+
+	cl_git_pass(git_pool_init(&p, sizeof(git_oid), 100));
+
+	for (i = 1000; i < 10000; i++) {
+		cl_git_pass(git_pool_malloc(&p, 1, (void **)&oid));
+		for (j = 0; j < 8; j++)
+			oid_hex[j] = to_hex[(i >> (4 * j)) & 0x0f];
+		cl_git_pass(git_oid_fromstr(oid, oid_hex));
+	}
+
+	/* with fixed page size, allocation must end up with these values */
+	cl_assert(git_pool__open_pages(&p) == 0);
+	cl_assert(git_pool__full_pages(&p) == 90);
+
+	git_pool_clear(&p);
+}