Convert package filelists to an array instead of linked list

This accomplishes quite a few things with one rather invasive change.

1. Iteration is much more performant, due to a reduction in pointer
   chasing and linear item access.
2. Data structures are smaller- we no longer have the overhead of the
   linked list as the file struts are now laid out consecutively in
   memory.
3. Memory allocation has been massively reworked. Before, we would
   allocate three different pieces of memory per file item- the list
   struct, the file struct, and the copied filename. What this resulted
   in was massive fragmentation of memory when loading filelists since
   the memory allocator had to leave holes all over the place. The new
   situation here now removes the need for any list item allocation;
   allocates the file structs in contiguous memory (and reallocs as
   necessary), leaving only the strings as individually allocated. Tests
   using valgrind (massif) show some pretty significant memory
   reductions on the worst case `pacman -Ql > /dev/null` (366387 files
   on my machine):

   Before:
     Peak heap:   54,416,024 B
	 Useful heap: 36,840,692 B
	 Extra heap:  17,575,332 B

   After:
     Peak heap:   38,004,352 B
	 Useful heap: 28,101,347 B
	 Extra heap:   9,903,005 B

Several small helper methods have been introduced, including a list to
array conversion helper as well as a filelist merge sort that works
directly on arrays.

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 73 insertions, 13 deletions

diff --git a/lib/libalpm/be_package.c b/lib/libalpm/be_package.c
index 46bdaed0..0edaa5a3 100644
--- a/lib/libalpm/be_package.c
+++ b/lib/libalpm/be_package.c
@@ -223,6 +223,53 @@ static int parse_descfile(alpm_handle_t *handle, struct archive *a, alpm_pkg_t *
 	return 0;
 }
 
+static void files_merge(alpm_file_t a[], alpm_file_t b[], alpm_file_t c[],
+		size_t m, size_t n)
+{
+	size_t i = 0, j = 0, k = 0;
+	while(i < m && j < n) {
+		if(strcmp(a[i].name, b[j].name) < 0) {
+			c[k++] = a[i++];
+		} else {
+			c[k++] = b[j++];
+		}
+	}
+	while(i < m) {
+		c[k++] = a[i++];
+	}
+	while(j < n) {
+		c[k++] = b[j++];
+	}
+}
+
+static alpm_file_t *files_msort(alpm_file_t *files, size_t n)
+{
+	alpm_file_t *work;
+	size_t blocksize = 1;
+
+	CALLOC(work, n, sizeof(alpm_file_t), return NULL);
+
+	for(blocksize = 1; blocksize < n; blocksize *= 2) {
+		size_t i, max_extent = 0;
+		for(i = 0; i < n - blocksize; i += 2 * blocksize) {
+			/* this limits our actual merge to the length of the array, since we will
+			 * not likely be a perfect power of two. */
+			size_t right_blocksize = blocksize;
+			if(i + blocksize * 2 > n) {
+				right_blocksize = n - i - blocksize;
+			}
+			files_merge(files + i, files + i + blocksize, work + i,
+					blocksize, right_blocksize);
+			max_extent = i + blocksize + right_blocksize;
+		}
+		/* ensure we only copy what we actually touched on this merge pass,
+		 * no more, no less */
+		memcpy(files, work, max_extent * sizeof(alpm_file_t));
+	}
+	free(work);
+	return files;
+}
+
 /**
  * Load a package and create the corresponding alpm_pkg_t struct.
  * @param handle the context handle
@@ -241,7 +288,8 @@ alpm_pkg_t *_alpm_pkg_load_internal(alpm_handle_t *handle, const char *pkgfile,
 	struct archive_entry *entry;
 	alpm_pkg_t *newpkg = NULL;
 	struct stat st;
-	size_t files_count = 0;
+	size_t files_count = 0, files_size = 0;
+	alpm_file_t *files = NULL;
 
 	if(pkgfile == NULL || strlen(pkgfile) == 0) {
 		RET_ERR(handle, ALPM_ERR_WRONG_ARGS, NULL);
@@ -326,12 +374,26 @@ alpm_pkg_t *_alpm_pkg_load_internal(alpm_handle_t *handle, const char *pkgfile,
 			 * already been handled (for future possibilities) */
 		} else if(full) {
 			/* Keep track of all files for filelist generation */
-			alpm_file_t *file;
-			CALLOC(file, 1, sizeof(alpm_file_t), goto error);
-			STRDUP(file->name, entry_name, goto error);
-			file->size = archive_entry_size(entry);
-			file->mode = archive_entry_mode(entry);
-			newpkg->files = alpm_list_add(newpkg->files, file);
+			if(files_count >= files_size) {
+				size_t old_size = files_size;
+				if(files_size == 0) {
+					files_size = 4;
+				} else {
+					files_size *= 2;
+				}
+				files = realloc(files, sizeof(alpm_file_t) * files_size);
+				if(!files) {
+					ALLOC_FAIL(sizeof(alpm_file_t) * files_size);
+					goto error;
+				}
+				/* ensure all new memory is zeroed out, in both the initial
+				 * allocation and later reallocs */
+				memset(files + old_size, 0,
+						sizeof(alpm_file_t) * (files_size - old_size));
+			}
+			STRDUP(files[files_count].name, entry_name, goto error);
+			files[files_count].size = archive_entry_size(entry);
+			files[files_count].mode = archive_entry_mode(entry);
 			files_count++;
 		}
 
@@ -369,16 +431,14 @@ alpm_pkg_t *_alpm_pkg_load_internal(alpm_handle_t *handle, const char *pkgfile,
 	newpkg->handle = handle;
 
 	if(full) {
+		/* attempt to hand back any memory we don't need */
+		files = realloc(files, sizeof(alpm_file_t) * files_count);
 		/* "checking for conflicts" requires a sorted list, ensure that here */
 		_alpm_log(handle, ALPM_LOG_DEBUG, "sorting package filelist for %s\n", pkgfile);
-		newpkg->files = alpm_list_msort(newpkg->files, files_count,
-				_alpm_files_cmp);
+		newpkg->files.files = files_msort(files, files_count);
+		newpkg->files.count = files_count;
 		newpkg->infolevel = INFRQ_ALL;
 	} else {
-		/* get rid of any partial filelist we may have collected, it is invalid */
-		alpm_list_free_inner(newpkg->files, (alpm_list_fn_free)_alpm_files_free);
-		alpm_list_free(newpkg->files);
-		newpkg->files = NULL;
 		newpkg->infolevel = INFRQ_BASE | INFRQ_DESC;
 	}