[DTrace-devel] [PATCH v2 10/20] Optimize dt_strtab_insert() for empty string

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>

On 6/3/21 11:17 AM, Kris Van Hees wrote:
> This patch also clarifies that the string table will always have the
> empty string at offset 0.
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_strtab.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/libdtrace/dt_strtab.c b/libdtrace/dt_strtab.c
> index 9f5ae23f..ff32606f 100644
> --- a/libdtrace/dt_strtab.c
> +++ b/libdtrace/dt_strtab.c
> @@ -1,6 +1,6 @@
>   /*
>    * Oracle Linux DTrace.
> - * Copyright (c) 2006, 2020, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2006, 2021, Oracle and/or its affiliates. All rights reserved.
>    * Licensed under the Universal Permissive License v 1.0 as shown at
>    * http://oss.oracle.com/licenses/upl.
>    */
> @@ -65,6 +65,11 @@ dt_strtab_create(size_t bufsz)
>   	if (dt_strtab_grow(sp) == -1)
>   		goto err;
>   
> +	/*
> +	 * Pre-populate the string table with the empty string as frist string,
> +	 * at offset 0.  We use this guarantee in dt_strtab_insert() and
> +	 * dt_strtab_index().
> +	 */
>   	*sp->str_ptr++ = '\0';
>   	return sp;
>   
> @@ -192,7 +197,7 @@ dt_strtab_index(dt_strtab_t *sp, const char *str)
>   	ulong_t h;
>   
>   	if (str == NULL || str[0] == '\0')
> -		return 0; /* we keep a \0 at offset 0 to simplify things */
> +		return 0;	/* The empty string is always at offset 0. */
>   
>   	h = dt_strtab_hash(str, &len) % sp->str_hashsz;
>   
> @@ -212,6 +217,9 @@ dt_strtab_insert(dt_strtab_t *sp, const char *str)
>   	ssize_t off;
>   	ulong_t h;
>   
> +	if (str == NULL || str[0] == '\0')
> +		return 0;	/* The empty string is always at offset 0. */
> +
>   	if ((off = dt_strtab_index(sp, str)) != -1)
>   		return off;
>