Robert Iakobashvili re-arranged the internal hash code to work with a custom

hash function for different hashes, and also expanded the default size for
the socket hash table used in multi handles to greatly enhance speed when
very many connections are added and the socket API is used.

lib/multi.c

@@ -50,6 +50,15 @@
 /* The last #include file should be: */
 #include "memdebug.h"
 
+/*
+  CURL_SOCKET_HASH_TABLE_SIZE should be a prime number. Increasing it from 97
+  to 911 takes on a 32-bit machine 4 x 804 = 3211 more bytes.  Still, every
+  CURL handle takes 45-50 K memory, therefore this 3K are not significant.
+*/
+#ifndef CURL_SOCKET_HASH_TABLE_SIZE
+#define CURL_SOCKET_HASH_TABLE_SIZE 911
+#endif
+
 struct Curl_message {
   /* the 'CURLMsg' is the part that is visible to the external user */
   struct CURLMsg extmsg;
@@ -305,6 +314,21 @@ static void sh_freeentry(void *freethis)
   free(p);
 }
 
+static size_t fd_key_compare(void*k1, size_t k1_len, void*k2, size_t k2_len)
+{
+  (void) k1_len; (void) k2_len;
+
+  return ((*((int* ) k1)) == (*((int* ) k2))) ? 1 : 0;
+}
+
+static size_t hash_fd(void* key, size_t key_length, size_t slots_num)
+{
+  int fd = * ((int* ) key);
+  (void) key_length;
+
+  return (fd % (int)slots_num);
+}
+
 /*
  * sh_init() creates a new socket hash and returns the handle for it.
  *
@@ -325,7 +349,8 @@ static void sh_freeentry(void *freethis)
  */
 static struct curl_hash *sh_init(void)
 {
-  return Curl_hash_alloc(97, sh_freeentry);
+  return Curl_hash_alloc(CURL_SOCKET_HASH_TABLE_SIZE, hash_fd, fd_key_compare,
+                         sh_freeentry);
 }
 
 CURLM *curl_multi_init(void)