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tree allocator routines



Talloc is a hierarchical memory pool system with destructors: you keep your objects in heirarchies reflecting their lifetime. Every pointer returned from talloc() is itself a valid talloc context, from which other talloc()s can be attached. This means you can do this:

 struct foo *X = talloc(mem_ctx, struct foo);
 X->name = talloc_strdup(X, "foo");

and the pointer X->name would be a "child" of the talloc context "X" which is itself a child of mem_ctx. So if you do talloc_free(mem_ctx) then it is all destroyed, whereas if you do talloc_free(X) then just X and X->name are destroyed, and if you do talloc_free(X->name) then just the name element of X is destroyed.

If you think about this, then what this effectively gives you is an n-ary tree, where you can free any part of the tree with talloc_free().

Talloc has been measured with a time overhead of around 4% over glibc malloc, and 48/80 bytes per allocation (32/64 bit).

This version is based on svn:// revision 23158.


#include <stdio.h>
#include <stdarg.h>
#include <err.h>
#include <ccan/talloc/talloc.h>

// A structure containing a popened command.
struct command
        FILE *f;
        const char *command;

// When struct command is freed, we also want to pclose pipe.
static int close_cmd(struct command *cmd)
        // 0 means "we succeeded, continue freeing"
        return 0;

// This function opens a writable pipe to the given command.
static struct command *open_output_cmd(const void *ctx,
                                       const char *fmt, ...)
        va_list ap;
        struct command *cmd = talloc(ctx, struct command);

        if (!cmd)
                return NULL;

        va_start(ap, fmt);
        cmd->command = talloc_vasprintf(cmd, fmt, ap);
        if (!cmd->command) {
                return NULL;

        cmd->f = popen(cmd->command, "w");
        if (!cmd->f) {
                return NULL;
        talloc_set_destructor(cmd, close_cmd);
        return cmd;

int main(int argc, char *argv[])
        struct command *cmd;

        if (argc != 2)
                errx(1, "Usage: %s <command>\n", argv[0]);

        cmd = open_output_cmd(NULL, "%s hello", argv[1]);
        if (!cmd)
                err(1, "Running '%s hello'", argv[1]);
        fprintf(cmd->f, "This is a test\n");
        return 0;


LGPL (v2.1 or any later version)