global_init: move the IPv6 works status bool to multi handle

Previously it was stored in a global state which contributed to
curl_global_init's thread unsafety. This boolean is now instead figured
out in curl_multi_init() and stored in the multi handle. Less effective,
but thread safe.

Closes #4851

8 files changed, 27 insertions, 25 deletions

diff --git a/lib/asyn-ares.c b/lib/asyn-ares.c
index ed52a740b..b76e66548 100644
--- a/lib/asyn-ares.c
+++ b/lib/asyn-ares.c
@@ -669,7 +669,7 @@ Curl_addrinfo *Curl_resolver_getaddrinfo(struct connectdata *conn,
     res->last_status = ARES_ENOTFOUND;
 #ifdef ENABLE_IPV6 /* CURLRES_IPV6 */
     if(family == PF_UNSPEC) {
-      if(Curl_ipv6works()) {
+      if(Curl_ipv6works(conn)) {
         res->num_pending = 2;
 
         /* areschannel is already setup in the Curl_open() function */
diff --git a/lib/asyn-thread.c b/lib/asyn-thread.c
index d11573860..6a6dce107 100644
--- a/lib/asyn-thread.c
+++ b/lib/asyn-thread.c
@@ -743,7 +743,7 @@ Curl_addrinfo *Curl_resolver_getaddrinfo(struct connectdata *conn,
     break;
   }
 
-  if((pf != PF_INET) && !Curl_ipv6works())
+  if((pf != PF_INET) && !Curl_ipv6works(conn))
     /* The stack seems to be a non-IPv6 one */
     pf = PF_INET;
 #endif /* CURLRES_IPV6 */
diff --git a/lib/easy.c b/lib/easy.c
index 0ad33c02b..98646c9c4 100644
--- a/lib/easy.c
+++ b/lib/easy.c
@@ -185,8 +185,6 @@ static CURLcode global_init(long flags, bool memoryfuncs)
     goto fail;
   }
 
-  (void)Curl_ipv6works();
-
 #if defined(USE_SSH)
   if(Curl_ssh_init()) {
     goto fail;
diff --git a/lib/hostip.h b/lib/hostip.h
index e0597ea96..a1c343ad7 100644
--- a/lib/hostip.h
+++ b/lib/hostip.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -96,9 +96,9 @@ int Curl_resolv_timeout(struct connectdata *conn, const char *hostname,
 /*
  * Curl_ipv6works() returns TRUE if IPv6 seems to work.
  */
-bool Curl_ipv6works(void);
+bool Curl_ipv6works(struct connectdata *conn);
 #else
-#define Curl_ipv6works() FALSE
+#define Curl_ipv6works(x) FALSE
 #endif
 
 /*
diff --git a/lib/hostip6.c b/lib/hostip6.c
index e0e0c58df..41ff98696 100644
--- a/lib/hostip6.c
+++ b/lib/hostip6.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -62,13 +62,19 @@
 /*
  * Curl_ipv6works() returns TRUE if IPv6 seems to work.
  */
-bool Curl_ipv6works(void)
+bool Curl_ipv6works(struct connectdata *conn)
 {
-  /* the nature of most system is that IPv6 status doesn't come and go
-     during a program's lifetime so we only probe the first time and then we
-     have the info kept for fast re-use */
-  static int ipv6_works = -1;
-  if(-1 == ipv6_works) {
+  if(conn) {
+    /* the nature of most system is that IPv6 status doesn't come and go
+       during a program's lifetime so we only probe the first time and then we
+       have the info kept for fast re-use */
+    DEBUGASSERT(conn);
+    DEBUGASSERT(conn->data);
+    DEBUGASSERT(conn->data->multi);
+    return conn->data->multi->ipv6_works;
+  }
+  else {
+    int ipv6_works = -1;
     /* probe to see if we have a working IPv6 stack */
     curl_socket_t s = socket(PF_INET6, SOCK_DGRAM, 0);
     if(s == CURL_SOCKET_BAD)
@@ -78,8 +84,8 @@ bool Curl_ipv6works(void)
       ipv6_works = 1;
       Curl_closesocket(NULL, s);
     }
+    return (ipv6_works>0)?TRUE:FALSE;
   }
-  return (ipv6_works>0)?TRUE:FALSE;
 }
 
 /*
@@ -89,7 +95,7 @@ bool Curl_ipv6works(void)
 bool Curl_ipvalid(struct connectdata *conn)
 {
   if(conn->ip_version == CURL_IPRESOLVE_V6)
-    return Curl_ipv6works();
+    return Curl_ipv6works(conn);
 
   return TRUE;
 }
@@ -159,7 +165,7 @@ Curl_addrinfo *Curl_getaddrinfo(struct connectdata *conn,
     break;
   }
 
-  if((pf != PF_INET) && !Curl_ipv6works())
+  if((pf != PF_INET) && !Curl_ipv6works(conn))
     /* The stack seems to be a non-IPv6 one */
     pf = PF_INET;
 
diff --git a/lib/multi.c b/lib/multi.c
index 1b79d42a4..b641074d4 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -370,6 +370,7 @@ struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
   /* -1 means it not set by user, use the default value */
   multi->maxconnects = -1;
   multi->max_concurrent_streams = 100;
+  multi->ipv6_works = Curl_ipv6works(NULL);
 
 #ifdef ENABLE_WAKEUP
   if(Curl_socketpair(AF_UNIX, SOCK_STREAM, 0, multi->wakeup_pair) < 0) {
diff --git a/lib/multihandle.h b/lib/multihandle.h
index b0cd0b821..91eca16c4 100644
--- a/lib/multihandle.h
+++ b/lib/multihandle.h
@@ -119,11 +119,6 @@ struct Curl_multi {
      same actual socket) */
   struct curl_hash sockhash;
 
-  /* multiplexing wanted */
-  bool multiplexing;
-
-  bool recheckstate; /* see Curl_multi_connchanged */
-
   /* Shared connection cache (bundles)*/
   struct conncache conn_cache;
 
@@ -141,13 +136,17 @@ struct Curl_multi {
   void *timer_userp;
   struct curltime timer_lastcall; /* the fixed time for the timeout for the
                                     previous callback */
-  bool in_callback;            /* true while executing a callback */
   unsigned int max_concurrent_streams;
 
 #ifdef ENABLE_WAKEUP
   curl_socket_t wakeup_pair[2]; /* socketpair() used for wakeup
                                    0 is used for read, 1 is used for write */
 #endif
+  /* multiplexing wanted */
+  bool multiplexing;
+  bool recheckstate; /* see Curl_multi_connchanged */
+  bool in_callback;            /* true while executing a callback */
+  bool ipv6_works;
 };
 
 #endif /* HEADER_CURL_MULTIHANDLE_H */
diff --git a/tests/data/test558 b/tests/data/test558
index 49ef1c70b..dccb8080a 100644
--- a/tests/data/test558
+++ b/tests/data/test558
@@ -36,8 +36,6 @@ nothing
 # Verify data after the test has been "shot"
 <verify>
 <file name="log/memdump">
-FD hostip6.c: socket()
-FD connect.c: sclose()
 MEM lib558.c: malloc()
 MEM lib558.c: free()
 MEM escape.c: malloc()