use hashtable instead of linked list to cache winsock errors

as discussed here:
https://github.com/libevent/libevent/pull/41#issuecomment-13611817

diff --git a/evutil.c b/evutil.c
index 655a5b9361db7f6ab8843a37f93d0e713a132d3a..ce39eda1a6e615bd1d316d560a19f9aa34d0990b 100644 (file)
--- a/evutil.c
+++ b/evutil.c
@@ -87,6 +87,8 @@
 #include "ipv6-internal.h"
 
 #ifdef _WIN32
+#define HT_NO_CACHE_HASH_VALUES
+#include "ht-internal.h"
 #define open _open
 #define read _read
 #define close _close
@@ -1620,32 +1622,70 @@ chomp (char *s)
  * only expect there to be a few dozen, and that should be fast enough.
  */
 
-struct cached_sock_errs {
+struct cached_sock_errs_entry {
+       HT_ENTRY(cached_sock_errs_entry) node;
        DWORD code;
        char *msg; /* allocated with LocalAlloc; free with LocalFree */
-       struct cached_sock_errs *next;
 };
 
+static inline unsigned
+hash_cached_sock_errs(const struct cached_sock_errs_entry *e)
+{
+       /* Use Murmur3's 32-bit finalizer as an integer hash function */
+       DWORD h = e->code;
+       h ^= h >> 16;
+       h *= 0x85ebca6b;
+       h ^= h >> 13;
+       h *= 0xc2b2ae35;
+       h ^= h >> 16;
+       return h;
+}
+
+static inline int
+eq_cached_sock_errs(const struct cached_sock_errs_entry *a,
+                   const struct cached_sock_errs_entry *b)
+{
+       return a->code == b->code;
+}
+
 #ifndef EVENT__DISABLE_THREAD_SUPPORT
 static void *windows_socket_errors_lock_ = NULL;
 #endif
 
-static struct cached_sock_errs *windows_socket_errors;
+static HT_HEAD(cached_sock_errs_map, cached_sock_errs_entry)
+     windows_socket_errors = HT_INITIALIZER();
+
+HT_PROTOTYPE(cached_sock_errs_map,
+            cached_sock_errs_entry,
+            node,
+            hash_cached_sock_errs,
+            eq_cached_sock_errs);
+
+HT_GENERATE(cached_sock_errs_map,
+           cached_sock_errs_entry,
+           node,
+           hash_cached_sock_errs,
+           eq_cached_sock_errs,
+           0.5,
+           mm_malloc,
+           mm_realloc,
+           mm_free);
 
 /** Equivalent to strerror, but for windows socket errors. */
 const char *
 evutil_socket_error_to_string(int errcode)
 {
-       struct cached_sock_errs *errs, *newerr;
+       struct cached_sock_errs_entry *errs, *newerr, find;
        char *msg = NULL;
 
        EVLOCK_LOCK(windows_socket_errors_lock_, 0);
 
-       for (errs = windows_socket_errors; errs != NULL; errs = errs->next)
-               if (errs->code == errcode) {
-                       msg = errs->msg;
-                       goto done;
-               }
+       find.code = errcode;
+       errs = HT_FIND(cached_sock_errs_map, &windows_socket_errors, &find);
+       if (errs) {
+               msg = errs->msg;
+               goto done;
+       }
 
        if (0 != FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM |
                               FORMAT_MESSAGE_IGNORE_INSERTS |
@@ -1663,8 +1703,8 @@ evutil_socket_error_to_string(int errcode)
                evutil_snprintf(msg, len, "winsock error 0x%08x", errcode);
        }
 
-       newerr = (struct cached_sock_errs *)
-               mm_malloc(sizeof (struct cached_sock_errs));
+       newerr = (struct cached_sock_errs_entry *)
+               mm_malloc(sizeof (struct cached_sock_errs_entry));
 
        if (!newerr) {
                LocalFree(msg);
@@ -1674,8 +1714,7 @@ evutil_socket_error_to_string(int errcode)
 
        newerr->code = errcode;
        newerr->msg = msg;
-       newerr->next = windows_socket_errors;
-       windows_socket_errors = newerr;
+       HT_INSERT(cached_sock_errs_map, &windows_socket_errors, newerr);
 
  done:
        EVLOCK_UNLOCK(windows_socket_errors_lock_, 0);
@@ -1695,16 +1734,19 @@ evutil_global_setup_locks_(const int enable_locks)
 static void
 evutil_free_sock_err_globals(void)
 {
-       struct cached_sock_errs *errs, *tofree;
+       struct cached_sock_errs_entry **errs, *tofree;
 
-       for (errs = windows_socket_errors; errs != NULL; ) {
-               LocalFree (errs->msg);
-               tofree = errs;
-               errs = errs->next;
-               mm_free (tofree);
+       for (errs = HT_START(cached_sock_errs_map, &windows_socket_errors)
+                    ; errs; ) {
+               tofree = *errs;
+               errs = HT_NEXT_RMV(cached_sock_errs_map,
+                                  &windows_socket_errors,
+                                  errs);
+               LocalFree(tofree->msg);
+               mm_free(tofree);
        }
 
-       windows_socket_errors = NULL;
+       HT_CLEAR(cached_sock_errs_map, &windows_socket_errors);
 
 #ifndef EVENT__DISABLE_THREAD_SUPPORT
        if (windows_socket_errors_lock_ != NULL) {