network: response stacking for all commands

This change refactors most of memcached's networking frontend code. The
goals with this change:

- Decouple buffer memory from client connections where plausible,
reducing memory usage for currently inactive TCP sessions.
- Allow easy response stacking for all protocols. Previously every
binary command generates a syscall during response. This is no longer
true when multiple commands are read off the wire at once. The new meta
protocol and most text protocol commands are similar.
- Reduce code complexity for network handling. Remove automatic buffer
adjustments, error checking, and so on.

This is accomplished by removing the iovec, msg, and "write buffer"
structures from connection objects. A `mc_resp` object is now used to
represent an individual response. These objects contain small iovec's
and enough detail to be late-combined on transmit. As a side effect,
UDP mode now works with extstore :)

Adding to the iovec always had a remote chance of memory failure, so
every call had to be checked for an error. Now once a response object
is allocated, most manipulations can happen without any checking. This
is both a boost to code robustness and performance for some hot paths.

This patch is the first in a series, focusing on the client response.

1 files changed, 2 insertions, 1 deletions

diff --git a/cache.c b/cache.c
index 0ccda9c..ea3115a 100644
--- a/cache.c
+++ b/cache.c
@@ -92,6 +92,7 @@ void* do_cache_alloc(cache_t *cache) {
                 free(ret);
                 object = NULL;
             }
+            cache->total++;
         }
     }
 
@@ -148,7 +149,7 @@ void do_cache_free(cache_t *cache, void *ptr) {
                 cache->destructor(ptr, NULL);
             }
             free(ptr);
-
+            cache->total--;
         }
     }
 }