In libpq for Windows, call WSAStartup once and WSACleanup not at all.

The Windows documentation insists that every WSAStartup call should
have a matching WSACleanup call.  However, if that ever had actual
relevance, it wasn't in this century.  Every remotely-modern Windows
kernel is capable of cleaning up when a process exits without doing
that, and must be so to avoid resource leaks in case of a process
crash.  Moreover, Postgres backends have done WSAStartup without
WSACleanup since commit 4cdf51e64 in 2004, and we've never seen any
indication of a problem with that.

libpq's habit of doing WSAStartup during connection start and
WSACleanup during shutdown is also rather inefficient, since a
series of non-overlapping connection requests leads to repeated,
quite expensive DLL unload/reload cycles.  We document a workaround
for that (having the application call WSAStartup for itself), but
that's just a kluge.  It's also worth noting that it's far from
uncommon for applications to exit without doing PQfinish, and
we've not heard reports of trouble from that either.

However, the real reason for acting on this is that recent
experiments by Alexander Lakhin show that calling WSACleanup
during PQfinish is triggering the symptom we occasionally see
that a process using libpq fails to emit expected stdio output.

Therefore, let's change libpq so that it calls WSAStartup only
once per process, during the first connection attempt, and never
calls WSACleanup at all.

While at it, get rid of the only other WSACleanup call in our code
tree, in pg_dump/parallel.c; that presumably is equally useless.

Back-patch of HEAD commit 7d00a6b2d.

Discussion: https://postgr.es/m/ac976d8c-03df-d6b8-025c-15a2de8d9af1@postgrespro.ru

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 85a9955542b5e464623ca9590166c81ed52c3d92..a88577c7b7c246eb88825b340f3cf5bfd31a75a4 100644 (file)
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -91,21 +91,6 @@
     </para>
    </warning>
 
-   <note>
-    <para>
-     On Windows, there is a way to improve performance if a single
-     database connection is repeatedly started and shutdown.  Internally,
-     libpq calls <function>WSAStartup()</> and <function>WSACleanup()</> for connection startup
-     and shutdown, respectively.  <function>WSAStartup()</> increments an internal
-     Windows library reference count which is decremented by <function>WSACleanup()</>.
-     When the reference count is just one, calling <function>WSACleanup()</> frees
-     all resources and all DLLs are unloaded.  This is an expensive
-     operation.  To avoid this, an application can manually call
-     <function>WSAStartup()</> so resources will not be freed when the last database
-     connection is closed.
-    </para>
-   </note>
-
    <variablelist>
     <varlistentry id="libpq-pqconnectdbparams">
      <term><function>PQconnectdbParams</function><indexterm><primary>PQconnectdbParams</></></term>

diff --git a/src/bin/pg_dump/parallel.c b/src/bin/pg_dump/parallel.c
index 12f714374ca30fe4143b850021bab1248d401146..fa95c2d5e651ecbec3c9089e39e8f71a25cb6962 100644 (file)
--- a/src/bin/pg_dump/parallel.c
+++ b/src/bin/pg_dump/parallel.c
@@ -192,19 +192,6 @@ static char *readMessageFromPipe(int fd);
        (strcmp(msg, pattern) == 0)
 
 
-/*
- * Shutdown callback to clean up socket access
- */
-#ifdef WIN32
-static void
-shutdown_parallel_dump_utils(int code, void *unused)
-{
-       /* Call the cleanup function only from the main thread */
-       if (mainThreadId == GetCurrentThreadId())
-               WSACleanup();
-}
-#endif
-
 /*
  * Initialize parallel dump support --- should be called early in process
  * startup.  (Currently, this is called whether or not we intend parallel
@@ -230,8 +217,7 @@ init_parallel_dump_utils(void)
                        fprintf(stderr, _("%s: WSAStartup failed: %d\n"), progname, err);
                        exit_nicely(1);
                }
-               /* ... and arrange to shut it down at exit */
-               on_exit_nicely(shutdown_parallel_dump_utils, NULL);
+
                parallel_init_done = true;
        }
 #endif

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 894162efd84e162f72ccddac5ab7cd376bd5a76a..26d489944c79839892b2181a30c0f870cd67f710 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2911,23 +2911,30 @@ makeEmptyPGconn(void)
 #ifdef WIN32
 
        /*
-        * Make sure socket support is up and running.
+        * Make sure socket support is up and running in this process.
+        *
+        * Note: the Windows documentation says that we should eventually do a
+        * matching WSACleanup() call, but experience suggests that that is at
+        * least as likely to cause problems as fix them.  So we don't.
         */
-       WSADATA         wsaData;
+       static bool wsastartup_done = false;
 
-       if (WSAStartup(MAKEWORD(1, 1), &wsaData))
-               return NULL;
+       if (!wsastartup_done)
+       {
+               WSADATA         wsaData;
+
+               if (WSAStartup(MAKEWORD(1, 1), &wsaData) != 0)
+                       return NULL;
+               wsastartup_done = true;
+       }
+
+       /* Forget any earlier error */
        WSASetLastError(0);
-#endif
+#endif                                                 /* WIN32 */
 
        conn = (PGconn *) malloc(sizeof(PGconn));
        if (conn == NULL)
-       {
-#ifdef WIN32
-               WSACleanup();
-#endif
                return conn;
-       }
 
        /* Zero all pointers and booleans */
        MemSet(conn, 0, sizeof(PGconn));
@@ -3076,10 +3083,6 @@ freePGconn(PGconn *conn)
        termPQExpBuffer(&conn->workBuffer);
 
        free(conn);
-
-#ifdef WIN32
-       WSACleanup();
-#endif
 }
 
 /*