Re: [PATCH 2/4] short circuit out of a few places where we would allocate zero bytes

From: Junio C Hamano <junkio@cox.net>
Date: Dec 28, 2005, 05:07 UTC
Message-ID: <7vpsnh24j3.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <Pine.LNX.4.64.0512272036380.14098@g5.osdl.org>

Linus Torvalds <torvalds@osdl.org> writes:

> That said, I think that would be preferable to changing the source code to 
> unnecessarily avoid zero-sized allocations.

Yes, that has essentially been the plan (according to the discussion lead to 7e4a2a848377241b8fb4f624d1151bbf2f8d5814 commit on the list).

After eradicating zero-sized allocations where that change makes the overall code cleaner (which Johannes and Eric did most of the heavylifting and I think mostly done), we would apply something like this, instead of doing x*alloc(size ? size : 1) at the calling site.

About die(), I think the current code structure is fine. If we were doing a library, propagating NULL from C library *alloc() back to our caller and having the caller deal with it is the right thing, but most of the callers of x*alloc() are our main programs and there aren't much they can do when we run out of memory.

---

diff --git a/git-compat-util.h b/git-compat-util.h
index 0c98c99..a71728e 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -63,6 +63,8 @@ extern char *gitstrcasestr(const char *h
 static inline void *xmalloc(size_t size)
 {
 	void *ret = malloc(size);
+	if (!ret && !size)
+		ret = malloc(1); /* funny c library */
 	if (!ret)
 		die("Out of memory, malloc failed");
 	return ret;
@@ -71,6 +73,8 @@ static inline void *xmalloc(size_t size)
 static inline void *xrealloc(void *ptr, size_t size)
 {
 	void *ret = realloc(ptr, size);
+	if (!ret && !size)
+		ret = realloc(ptr, 1); /* funny c library */
 	if (!ret)
 		die("Out of memory, realloc failed");
 	return ret;
@@ -79,6 +83,8 @@ static inline void *xrealloc(void *ptr, 
 static inline void *xcalloc(size_t nmemb, size_t size)
 {
 	void *ret = calloc(nmemb, size);
+	if (!ret && (!nmemb || !size))
+		ret = calloc(1, 1); /* funny c library */
 	if (!ret)
 		die("Out of memory, calloc failed");
 	return ret;