--- /dev/null
+#include <stdio.h>
+#include <string.h>
+#include "config.h"
+
+/**
+ * talloc_link - link helper for talloc
+ *
+ * Talloc references can be confusing and buggy. In the cases where an object
+ * needs multiple parents, all parents need to be aware of the situation; thus
+ * talloc_link is a helper where all "parents" talloc_link an object they
+ * agree to share ownership of.
+ *
+ * Example:
+ * // Silly program which keeps a cache of uppercased strings.
+ * // The cache wants to keep strings around even after they may have
+ * // been "freed" by the caller.
+ * #include <stdio.h>
+ * #include <err.h>
+ * #include <string.h>
+ * #include <ctype.h>
+ * #include <ccan/talloc/talloc.h>
+ * #include <ccan/talloc_link/talloc_link.h>
+ *
+ * struct upcache {
+ * const char *str;
+ * const char *upstr;
+ * };
+ *
+ * static struct upcache *cache;
+ * static unsigned int cache_hits = 0;
+ * #define CACHE_SIZE 4
+ * void init_upcase(void)
+ * {
+ * cache = talloc_zero_array(NULL, struct upcache, CACHE_SIZE);
+ * }
+ *
+ * static struct upcache *lookup_upcase(const char *str)
+ * {
+ * unsigned int i;
+ * for (i = 0; i < CACHE_SIZE; i++)
+ * if (cache[i].str && !strcmp(cache[i].str, str)) {
+ * cache_hits++;
+ * return &cache[i];
+ * }
+ * return NULL;
+ * }
+ *
+ * static struct upcache *new_upcase(const char *str)
+ * {
+ * unsigned int i;
+ * char *upstr;
+ *
+ * upstr = talloc_linked(cache, talloc_strdup(NULL, str));
+ * if (!upstr)
+ * return NULL;
+ *
+ * i = random() % CACHE_SIZE;
+ *
+ * // Throw out old: works fine if cache[i].upstr is NULL.
+ * talloc_delink(cache, cache[i].upstr);
+ *
+ * // Replace with new.
+ * cache[i].str = str;
+ * cache[i].upstr = upstr;
+ * while (*upstr) {
+ * *upstr = toupper(*upstr);
+ * upstr++;
+ * }
+ * return &cache[i];
+ * }
+ *
+ * // If you want to keep the result, talloc_link it.
+ * const char *get_upcase(const char *str)
+ * {
+ * struct upcache *uc = lookup_upcase(str);
+ * if (!uc)
+ * uc = new_upcase(str);
+ * if (!uc)
+ * return NULL;
+ * return uc->upstr;
+ * }
+ *
+ * void exit_upcase(void)
+ * {
+ * talloc_free(cache);
+ * printf("Cache hits: %u\n", cache_hits);
+ * }
+ *
+ * int main(int argc, char *argv[])
+ * {
+ * unsigned int i;
+ * const char **values;
+ *
+ * // Will dump any memory leaks to stderr on exit.
+ * talloc_enable_leak_report();
+ *
+ * // Initialize cache.
+ * init_upcase();
+ *
+ * // Throw values in.
+ * values = talloc_array(NULL, const char *, argc);
+ * for (i = 1; i < argc; i++) {
+ * values[i-1] = talloc_link(values, get_upcase(argv[i]));
+ * if (!values[i-1])
+ * err(1, "Out of memory");
+ * }
+ * // This will free all the values, but cache will still work.
+ * talloc_free(values);
+ *
+ * // Repeat!
+ * values = talloc_array(NULL, const char *, argc);
+ * for (i = 1; i < argc; i++) {
+ * values[i-1] = talloc_link(values, get_upcase(argv[i]));
+ * if (!values[i-1])
+ * err(1, "Out of memory");
+ * }
+ *
+ * // This will remove cache links, but we still have a link.
+ * exit_upcase();
+ *
+ * // Show values, so we output something.
+ * for (i = 0; i < argc - 1; i++)
+ * printf("%s ", values[i]);
+ * printf("\n");
+ *
+ * // This will finally free the upcase strings (last link).
+ * talloc_free(values);
+ *
+ * return 0;
+ * }
+ *
+ * Licence: GPL (2 or any later version)
+ */
+int main(int argc, char *argv[])
+{
+ if (argc != 2)
+ return 1;
+
+ if (strcmp(argv[1], "depends") == 0) {
+ printf("ccan/talloc\n");
+ printf("ccan/list\n");
+ return 0;
+ }
+
+ return 1;
+}
--- /dev/null
+#include <ccan/list/list.h>
+#include <ccan/talloc/talloc.h>
+#include <ccan/talloc_link/talloc_link.h>
+#include <assert.h>
+
+/* Fake parent, if they care. */
+static void *talloc_links = NULL;
+
+/* This is the parent of the linked object, so we can implement delink. */
+struct talloc_linked {
+ struct list_head links;
+ const void *obj;
+};
+
+/* This is a child of the linker, but not a parent of ref. */
+struct talloc_link {
+ struct list_node list;
+ struct talloc_linked *linked;
+};
+
+static int destroy_link(struct talloc_link *link)
+{
+ list_del(&link->list);
+ if (list_empty(&link->linked->links))
+ talloc_free(link->linked);
+ return 0;
+}
+
+static bool add_link(const void *ctx, struct talloc_linked *linked)
+{
+ struct talloc_link *link = talloc(ctx, struct talloc_link);
+ if (!link)
+ return false;
+
+ link->linked = linked;
+ list_add(&linked->links, &link->list);
+ talloc_set_destructor(link, destroy_link);
+ return true;
+}
+
+void *_talloc_linked(const void *ctx, const void *newobj)
+{
+ struct talloc_linked *linked;
+
+ if (talloc_parent(newobj)) {
+ /* Assume leak reporting is on: create dummy parent. */
+ if (!talloc_links)
+ talloc_links = talloc_named_const(NULL, 0,
+ "talloc_links");
+ /* This should now have same pseudo-NULL parent. */
+ assert(talloc_parent(newobj) == talloc_parent(talloc_links));
+ }
+
+ linked = talloc(talloc_links, struct talloc_linked);
+ if (!linked) {
+ talloc_free(newobj);
+ return NULL;
+ }
+ list_head_init(&linked->links);
+ linked->obj = talloc_steal(linked, newobj);
+
+ if (!add_link(ctx, linked)) {
+ talloc_free(linked);
+ return NULL;
+ }
+
+ return (void *)newobj;
+}
+
+void *_talloc_link(const void *ctx, const void *obj)
+{
+ struct talloc_linked *linked;
+
+ linked = talloc_get_type(talloc_parent(obj), struct talloc_linked);
+ assert(!list_empty(&linked->links));
+ return add_link(ctx, linked) ? (void *)obj : NULL;
+}
+
+void talloc_delink(const void *ctx, const void *obj)
+{
+ struct talloc_linked *linked;
+ struct talloc_link *i;
+
+ if (!obj)
+ return;
+
+ linked = talloc_get_type(talloc_parent(obj), struct talloc_linked);
+ list_for_each(&linked->links, i, list) {
+ if (talloc_is_parent(i, ctx)) {
+ talloc_free(i);
+ return;
+ }
+ }
+ abort();
+}
--- /dev/null
+#ifndef TALLOC_LINK_H
+#define TALLOC_LINK_H
+#include <ccan/talloc/talloc.h>
+
+/**
+ * talloc_linked - set up an object with an initial link.
+ * @ctx - the context to initially link to
+ * @newobj - the newly allocated object (with a NULL parent)
+ *
+ * The object will be freed when @ctx is freed (or talloc_delink(ctx,
+ * newobj) is called), unless more links are added using
+ * talloc_link().
+ *
+ * For convenient chaining, it returns @newobj on success, or frees
+ * @newobj and returns NULL.
+ */
+#define talloc_linked(ctx, newobj) \
+ ((_TALLOC_TYPEOF(newobj))_talloc_linked((ctx), (newobj)))
+
+/**
+ * talloc_link - add another link to a linkable object.
+ * @ctx - the context to link to
+ * @obj - the object previously made linkable with talloc_linked().
+ *
+ * The @obj will only be freed when all contexts linked to it are
+ * freed (or talloc_delink()ed).
+ *
+ * Returns @obj, or NULL on failure (out of memory).
+ */
+#define talloc_link(ctx, obj) \
+ ((_TALLOC_TYPEOF(obj))_talloc_link((ctx), (obj)))
+
+/**
+ * talloc_delink - explicitly remove a link from a linkable object.
+ * @ctx - the context previously used for talloc_link/talloc_linked
+ * @obj - the object previously used for talloc_link/talloc_linked
+ *
+ * Explicitly remove a link: normally it is implied by freeing @ctx.
+ * Removing the last link frees the object.
+ */
+void talloc_delink(const void *ctx, const void *linked);
+
+/* Internal helpers. */
+void *_talloc_link(const void *ctx, const void *linked);
+void *_talloc_linked(const void *ctx, const void *linked);
+
+#endif /* TALLOC_LINK_H */
--- /dev/null
+#include "talloc_link/talloc_link.h"
+#include "tap/tap.h"
+#include "talloc_link/talloc_link.c"
+#include <stdlib.h>
+#include <err.h>
+
+static unsigned int destroy_count = 0;
+static int destroy_obj(void *obj)
+{
+ destroy_count++;
+ return 0;
+}
+
+int main(int argc, char *argv[])
+{
+ void *obj, *p1, *p2, *p3;
+
+ plan_tests(16);
+
+ talloc_enable_leak_report();
+
+ /* Single parent case. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+
+ ok(destroy_count == 0, "destroy_count = %u", destroy_count);
+ talloc_free(p1);
+ ok(destroy_count == 1, "destroy_count = %u", destroy_count);
+
+ /* Dual parent case. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+ p2 = talloc(NULL, char);
+ talloc_link(p2, obj);
+
+ talloc_free(p1);
+ ok(destroy_count == 1, "destroy_count = %u", destroy_count);
+ talloc_free(p2);
+ ok(destroy_count == 2, "destroy_count = %u", destroy_count);
+
+ /* Triple parent case. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+
+ p2 = talloc(NULL, char);
+ p3 = talloc(NULL, char);
+
+ talloc_link(p2, obj);
+ talloc_link(p3, obj);
+
+ talloc_free(p1);
+ ok(destroy_count == 2, "destroy_count = %u", destroy_count);
+ talloc_free(p2);
+ ok(destroy_count == 2, "destroy_count = %u", destroy_count);
+ talloc_free(p3);
+ ok(destroy_count == 3, "destroy_count = %u", destroy_count);
+
+ /* Single delink case. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+
+ ok(destroy_count == 3, "destroy_count = %u", destroy_count);
+ talloc_delink(p1, obj);
+ ok(destroy_count == 4, "destroy_count = %u", destroy_count);
+ talloc_free(p1);
+
+ /* Double delink case. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+
+ p2 = talloc(NULL, char);
+ talloc_link(p2, obj);
+
+ talloc_delink(p1, obj);
+ ok(destroy_count == 4, "destroy_count = %u", destroy_count);
+ talloc_delink(p2, obj);
+ ok(destroy_count == 5, "destroy_count = %u", destroy_count);
+ talloc_free(p1);
+ talloc_free(p2);
+
+ /* Delink and free. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+ p2 = talloc(NULL, char);
+ talloc_link(p2, obj);
+
+ talloc_delink(p1, obj);
+ ok(destroy_count == 5, "destroy_count = %u", destroy_count);
+ talloc_free(p2);
+ ok(destroy_count == 6, "destroy_count = %u", destroy_count);
+ talloc_free(p1);
+
+ /* Free and delink. */
+ p1 = talloc(NULL, char);
+ obj = talloc_linked(p1, talloc(NULL, char));
+ talloc_set_destructor(obj, destroy_obj);
+ p2 = talloc(NULL, char);
+ talloc_link(p2, obj);
+
+ talloc_free(p1);
+ ok(destroy_count == 6, "destroy_count = %u", destroy_count);
+ talloc_delink(p2, obj);
+ ok(destroy_count == 7, "destroy_count = %u", destroy_count);
+ talloc_free(p2);
+
+ /* No leaks? */
+ ok1(talloc_total_size(NULL) == 0);
+
+ return exit_status();
+}
projects / ccan / commitdiff