[PATCH 2/2 v3] [libpq] Try to avoid manually masking SIGPIPEs on every send()

Currently, libpq will wrap each send() call on the connection with
two system calls to mask SIGPIPEs. This results in 3 syscalls instead
of one, and (on Linux) can lead to high contention on the signal
mask locks in threaded apps.

We have a couple of other methods to avoid SIGPIPEs:
sockopt(SO_NOSIGPIPE) and the MSG_NOSIGNAL flag to send().

This change attempts to use these if they're available at compile-
and run-time. If not, we drop back to manipulating the signal mask as
before.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

---src/interfaces/libpq/fe-connect.c |   40 ++++++++++++++++++src/interfaces/libpq/fe-secure.c  |   83
+++++++++++++++++++++++++++++---------src/interfaces/libpq/libpq-int.h |    2 3 files changed, 107 insertions(+), 18
deletions(-)

*** a/src/interfaces/libpq/fe-connect.c
--- b/src/interfaces/libpq/fe-connect.c
***************
*** 1085,1090 **** keep_going:                        /* We will come back to here until there is
--- 1085,1091 ----                 while (conn->addr_cur != NULL)                 {                     struct addrinfo
*addr_cur= conn->addr_cur;
 
+                     int optval;                      /* Remember current address for possible error msg */
        memcpy(&conn->raddr.addr, addr_cur->ai_addr,
 
***************
*** 1149,1154 **** keep_going:                        /* We will come back to here until there is
--- 1150,1194 ----                     } #endif   /* F_SETFD */ 
+                     /* We have three methods of blocking sigpipe during
+                      * send() calls to this socket:
+                      *
+                      *  - setsockopt(sock, SO_NOSIGPIPE)
+                      *  - send(sock, ..., MSG_NOSIGNAL)
+                      *  - setting the signal mask to SIG_IGN during send()
+                      *
+                      * The first two reduce the number of syscalls (for the
+                      * third, we require three syscalls to implement a send()),
+                      * so use them if they're available. Their availability is
+                      * flagged in the following members of PGconn:
+                      *
+                      * conn->sigpipe_so        - we have set up SO_NOSIGPIPE
+                      * conn->sigpipe_flag    - we're specifying MSG_NOSIGNAL
+                      *
+                      * If we can use SO_NOSIGPIPE, then set sigpipe_so here and
+                      * we don't need to care about anything else. Otherwise,
+                      * try MSG_NOSIGNAL by setting sigpipe_flag. If we get an
+                      * error with MSG_NOSIGNAL, we clear the flag and revert
+                      * to manual masking.
+                      */
+                     conn->sigpipe_so = false;
+ #ifdef MSG_NOSIGNAL
+                     conn->sigpipe_flag = true;
+ #else /* !MSG_NOSIGNAL */
+                     conn->sigpipe_flag = false;
+ #endif /* MSG_NOSIGNAL */
+ 
+ #ifdef SO_NOSIGPIPE
+                     optval = 1;
+                     if (!setsockopt(conn->sock, SOL_SOCKET, SO_NOSIGPIPE,
+                             (char *)&optval, sizeof(optval)))
+                     {
+                         conn->sigpipe_so = true;
+                         conn->sigpipe_flag = false;
+                     }
+ #endif /* SO_NOSIGPIPE */
+ 
+                      /*                      * Start/make connection.  This should not block, since we
     * are in nonblock mode.  If it does, well, too bad.
 
*** a/src/interfaces/libpq/fe-secure.c
--- b/src/interfaces/libpq/fe-secure.c
***************
*** 122,127 **** static long win32_ssl_create_mutex = 0;
--- 122,139 ----  */  #ifndef WIN32
+ 
+ static inline int sigpipe_masked(PGconn *conn)
+ {
+     /* If we're on an SSL connection, we can only use SO_NOSIGPIPE masking.
+      * Otherwise, we can handle SO_NOSIGPIPE or the MSG_NOSIGNAL flag */
+ #ifdef USE_SSL
+     if (conn->ssl)
+         return conn->sigpipe_so;
+ #endif
+     return conn->sigpipe_so || conn->sigpipe_flag;
+ }
+  #ifdef ENABLE_THREAD_SAFETY  struct sigpipe_info {
***************
*** 130,137 **** struct sigpipe_info {     bool        got_epipe; }; 
! static inline int disable_sigpipe(struct sigpipe_info *info) {     info->got_epipe = false;     return
pq_block_sigpipe(&info->oldsigmask,&info->sigpipe_pending) < 0; }
 
--- 142,152 ----     bool        got_epipe; }; 
! static inline int disable_sigpipe(PGconn *conn, struct sigpipe_info *info) {
+     if (sigpipe_masked(conn))
+         return 0;
+      info->got_epipe = false;     return pq_block_sigpipe(&info->oldsigmask, &info->sigpipe_pending) < 0; }
***************
*** 142,149 **** static inline void remember_epipe(struct sigpipe_info *info, bool cond)         info->got_epipe =
true;} 
 
! static inline void restore_sigpipe(struct sigpipe_info *info) {     pq_reset_sigpipe(&info->oldsigmask,
info->sigpipe_pending,info->got_epipe); } 
 
--- 157,167 ----         info->got_epipe = true; } 
! static inline void restore_sigpipe(PGconn *conn, struct sigpipe_info *info) {
+     if (sigpipe_masked(conn))
+         return;
+      pq_reset_sigpipe(&info->oldsigmask, info->sigpipe_pending, info->got_epipe); } 
***************
*** 153,161 **** struct sigpipe_info {     pqsigfunc    oldhandler; }; 
! static inline int disable_sigpipe(struct sigpipe_info *info) {
!     info->oldhandler = pqsignal(SIGPIPE, SIG_IGN);     return 0; } 
--- 171,180 ----     pqsigfunc    oldhandler; }; 
! static inline int disable_sigpipe(PGconn *conn, struct sigpipe_info *info) {
!     if (!sigpipe_masked(conn))
!         info->oldhandler = pqsignal(SIGPIPE, SIG_IGN);     return 0; } 
***************
*** 163,180 **** static inline void remember_epipe(struct sigpipe_info *info, bool cond) { } 
! static inline void restore_sigpipe(struct sigpipe_info *info) {
!     pqsignal(SIGPIPE, info->oldhandler); }  #endif    /* ENABLE_THREAD_SAFETY */ #else    /* WIN32 */  struct
sigpipe_info{ };
 
! static inline int disable_sigpipe(struct sigpipe_info *info) { return 0; } static inline void remember_epipe(struct
sigpipe_info*info, bool cond) { }
 
! static inline void restore_sigpipe(struct sigpipe_info *info) { }  #endif    /* WIN32 */ 
--- 182,203 ---- { } 
! static inline void restore_sigpipe(PGconn *conn, struct sigpipe_info *info) {
!     if (!sigpipe_masked(conn))
!         pqsignal(SIGPIPE, info->oldhandler); }  #endif    /* ENABLE_THREAD_SAFETY */ #else    /* WIN32 */  struct
sigpipe_info{ };
 
! static inline int disable_sigpipe(PGConn *conn, struct sigpipe_info *info)
! {
!     return 0;
! } static inline void remember_epipe(struct sigpipe_info *info, bool cond) { }
! static inline void restore_sigpipe(PGConn *conn, struct sigpipe_info *info) { }  #endif    /* WIN32 */ 
***************
*** 306,312 **** pqsecure_read(PGconn *conn, void *ptr, size_t len)         struct sigpipe_info info;          /*
SSL_readcan write to the socket, so we need to disable SIGPIPE */
 
!         if (disable_sigpipe(&info))             return -1;  rloop:
--- 329,335 ----         struct sigpipe_info info;          /* SSL_read can write to the socket, so we need to disable
SIGPIPE*/
 
!         if (disable_sigpipe(conn, &info))             return -1;  rloop:
***************
*** 370,376 **** rloop:                 break;         } 
!         restore_sigpipe(&info);     }     else #endif
--- 393,399 ----                 break;         } 
!         restore_sigpipe(conn, &info);     }     else #endif
***************
*** 388,401 **** pqsecure_write(PGconn *conn, const void *ptr, size_t len)     ssize_t        n;     struct
sigpipe_infoinfo; 
 
-     if (disable_sigpipe(&info))
-         return -1;
-  #ifdef USE_SSL     if (conn->ssl)     {         int            err;          n = SSL_write(conn->ssl, ptr, len);
   err = SSL_get_error(conn->ssl, n);         switch (err)
 
--- 411,424 ----     ssize_t        n;     struct sigpipe_info info;  #ifdef USE_SSL     if (conn->ssl)     {
int           err; 
 
+         if (disable_sigpipe(conn, &info))
+             return -1;
+          n = SSL_write(conn->ssl, ptr, len);         err = SSL_get_error(conn->ssl, n);         switch (err)
***************
*** 458,468 **** pqsecure_write(PGconn *conn, const void *ptr, size_t len)     else #endif     {
!         n = send(conn->sock, ptr, len, 0);
!         remember_epipe(&info, n < 0 && SOCK_ERRNO == EPIPE);     } 
!     restore_sigpipe(&info);      return n; }
--- 481,515 ----     else #endif     {
!         int flags = 0;
! 
! #ifdef MSG_NOSIGNAL
!         if (!conn->sigpipe_so && conn->sigpipe_flag)
!             flags |= MSG_NOSIGNAL;
! #endif /* MSG_NOSIGNAL */
! 
! retry_masked:
!         if (disable_sigpipe(conn, &info))
!             return -1;
! 
!         n = send(conn->sock, ptr, len, flags);
! 
!         if (n < 0) {
!             /* if we see an EINVAL, it may be because MSG_NOSIGNAL isn't
!              * available on this machine. So, clear sigpipe_flag so we don't
!              * try this flag again, and retry the send().
!              */
!             if (flags != 0 && SOCK_ERRNO == EINVAL) {
!                 conn->sigpipe_flag = false;
!                 flags = 0;
!                 goto retry_masked;
!             }
! 
!             remember_epipe(&info, SOCK_ERRNO == EPIPE);
!         }     } 
!     restore_sigpipe(conn, &info);      return n; }
***************
*** 1219,1232 **** close_SSL(PGconn *conn)     if (conn->ssl)     {         struct sigpipe_info info;
!         disable_sigpipe(&info);         SSL_shutdown(conn->ssl);         SSL_free(conn->ssl);         conn->ssl =
NULL;        pqsecure_destroy();         /* We have to assume we got EPIPE */         remember_epipe(&info, true);
 
!         restore_sigpipe(&info);     }      if (conn->peer)
--- 1266,1279 ----     if (conn->ssl)     {         struct sigpipe_info info;
!         disable_sigpipe(conn, &info);         SSL_shutdown(conn->ssl);         SSL_free(conn->ssl);         conn->ssl
=NULL;         pqsecure_destroy();         /* We have to assume we got EPIPE */         remember_epipe(&info, true);
 
!         restore_sigpipe(conn, &info);     }      if (conn->peer)
*** a/src/interfaces/libpq/libpq-int.h
--- b/src/interfaces/libpq/libpq-int.h
***************
*** 336,341 **** struct pg_conn
--- 336,343 ----     ProtocolVersion pversion;    /* FE/BE protocol version in use */     int            sversion;
 /* server version, e.g. 70401 for 7.4.1 */     bool        password_needed;    /* true if server demanded a password
*/
+     bool        sigpipe_so;        /* have we masked sigpipes via SO_NOSIGPIPE? */
+     bool        sigpipe_flag;    /* can we mask sigpipes via MSG_NOSIGNAL? */      /* Transient state needed while
establishingconnection */     struct addrinfo *addrlist;    /* list of possible backend addresses */