Re: Fix for non-blocking connections in libpq - Mailing list pgsql-patches

Patch applied.  Thanks.  I got it merged into the current CVS.

---------------------------------------------------------------------------


Bernhard Herzog wrote:
>
> Here's a patch against 7.1.3 that fixes a problem with sending larger
> queries over non-blocking connections with libpq. "Larger" here
> basically means that it doesn't fit into the output buffer.
>
> The basic strategy is to fix pqFlush and pqPutBytes.
>
> The problem with pqFlush as it stands now is that it returns EOF when an
> error occurs or when not all data could be sent. The latter case is
> clearly not an error for a non-blocking connection but the caller can't
> distringuish it from an error very well.
>
> The first part of the fix is therefore to fix pqFlush. This is done by
> to renaming it to pqSendSome which only differs from pqFlush in its
> return values to allow the caller to make the above distinction and a
> new pqFlush which is implemented in terms of pqSendSome and behaves
> exactly like the old pqFlush.
>
> The second part of the fix modifies pqPutBytes to use pqSendSome instead
> of pqFlush and to either send all the data or if not all data can be
> sent on a non-blocking connection to at least put all data into the
> output buffer, enlarging it if necessary. The callers of pqPutBytes
> don't have to be changed because from their point of view pqPutBytes
> behaves like before. It either succeeds in queueing all output data or
> fails with an error.
>
> I've also added a new API function PQsendSome which analogously to
> PQflush just calls pqSendSome. Programs using non-blocking queries
> should use this new function. The main difference is that this function
> will have to be called repeatedly (calling select() properly in between)
> until all data has been written.
>
> AFAICT, the code in CVS HEAD hasn't changed with respect to non-blocking
> queries and this fix should work there, too, but I haven't tested that
> yet.
>
>
>    Bernhard
>
> diff -rc -x *.o postgresql-7.1.3-orig/src/interfaces/libpq/fe-exec.c postgresql-7.1.3/src/interfaces/libpq/fe-exec.c
> *** postgresql-7.1.3-orig/src/interfaces/libpq/fe-exec.c    Sat Feb 10 03:31:30 2001
> --- postgresql-7.1.3/src/interfaces/libpq/fe-exec.c    Tue Jan 22 12:12:58 2002
> ***************
> *** 2214,2216 ****
> --- 2214,2224 ----
>
>       return (pqFlush(conn));
>   }
> +
> + /* try to force data out, really only useful for non-blocking users.
> +  * This implementation actually works for non-blocking connections */
> + int
> + PQsendSome(PGconn *conn)
> + {
> +     return pqSendSome(conn);
> + }
> diff -rc -x *.o postgresql-7.1.3-orig/src/interfaces/libpq/fe-misc.c postgresql-7.1.3/src/interfaces/libpq/fe-misc.c
> *** postgresql-7.1.3-orig/src/interfaces/libpq/fe-misc.c    Sun Apr  1 01:13:30 2001
> --- postgresql-7.1.3/src/interfaces/libpq/fe-misc.c    Tue Jan 22 12:07:25 2002
> ***************
> *** 90,144 ****
>   static int
>   pqPutBytes(const char *s, size_t nbytes, PGconn *conn)
>   {
> !     size_t        avail = Max(conn->outBufSize - conn->outCount, 0);
> !
> !     /*
> !      * if we are non-blocking and the send queue is too full to buffer
> !      * this request then try to flush some and return an error
>        */
> -     if (pqIsnonblocking(conn) && nbytes > avail && pqFlush(conn))
> -     {
>
> !         /*
> !          * even if the flush failed we may still have written some data,
> !          * recalculate the size of the send-queue relative to the amount
> !          * we have to send, we may be able to queue it afterall even
> !          * though it's not sent to the database it's ok, any routines that
> !          * check the data coming from the database better call pqFlush()
> !          * anyway.
> !          */
> !         if (nbytes > Max(conn->outBufSize - conn->outCount, 0))
> !         {
> !             printfPQExpBuffer(&conn->errorMessage,
> !                            "pqPutBytes --  pqFlush couldn't flush enough"
> !                          " data: space available: %d, space needed %d\n",
> !                       Max(conn->outBufSize - conn->outCount, 0), nbytes);
> !             return EOF;
> !         }
> !         /* fixup avail for while loop */
>           avail = Max(conn->outBufSize - conn->outCount, 0);
> !     }
>
> !     /*
> !      * is the amount of data to be sent is larger than the size of the
> !      * output buffer then we must flush it to make more room.
> !      *
> !      * the code above will make sure the loop conditional is never true for
> !      * non-blocking connections
> !      */
> !     while (nbytes > avail)
> !     {
> !         memcpy(conn->outBuffer + conn->outCount, s, avail);
> !         conn->outCount += avail;
> !         s += avail;
> !         nbytes -= avail;
> !         if (pqFlush(conn))
> !             return EOF;
> !         avail = conn->outBufSize;
> !     }
>
> !     memcpy(conn->outBuffer + conn->outCount, s, nbytes);
> !     conn->outCount += nbytes;
>
>       return 0;
>   }
> --- 90,163 ----
>   static int
>   pqPutBytes(const char *s, size_t nbytes, PGconn *conn)
>   {
> !     /* Strategy to handle blocking and non-blocking connections: Fill
> !      * the output buffer and flush it repeatedly until either all data
> !      * has been sent or is at least queued in the buffer.
> !      *
> !      * For non-blocking connections, grow the buffer if not all data
> !      * fits into it and the buffer can't be sent because the socket
> !      * would block.
>        */
>
> !     while (nbytes)
> !     {
> !         size_t avail, remaining;
> !
> !         /* fill the output buffer */
>           avail = Max(conn->outBufSize - conn->outCount, 0);
> !         remaining = Min(avail, nbytes);
> !         memcpy(conn->outBuffer + conn->outCount, s, remaining);
> !         conn->outCount += remaining;
> !         s += remaining;
> !         nbytes -= remaining;
> !
> !         /* if the data didn't fit completely into the buffer, try to
> !          * flush the buffer */
> !         if (nbytes)
> !         {
> !             int send_result = pqSendSome(conn);
>
> !             /* if there were errors, report them */
> !             if (send_result < 0)
> !                 return EOF;
>
> !             /* if not all data could be sent, increase the output
> !              * buffer, put the rest of s into it and return
> !              * successfully. This case will only happen in a
> !              * non-blocking connection
> !              */
> !             if (send_result > 0)
> !             {
> !                 /* try to grow the buffer.
> !                  * FIXME: The new size could be chosen more
> !                  * intelligently.
> !                  */
> !                 size_t buflen = conn->outCount + nbytes;
> !                 if (buflen > conn->outBufSize)
> !                 {
> !                     char * newbuf = realloc(conn->outBuffer, buflen);
> !                     if (!newbuf)
> !                     {
> !                         /* realloc failed. Probably out of memory */
> !                         printfPQExpBuffer(&conn->errorMessage,
> !                                 "cannot allocate memory for output buffer\n");
> !                         return EOF;
> !                     }
> !                     conn->outBuffer = newbuf;
> !                     conn->outBufSize = buflen;
> !                 }
> !                 /* put the data into it */
> !                 memcpy(conn->outBuffer + conn->outCount, s, nbytes);
> !                 conn->outCount += nbytes;
> !
> !                 /* report success. */
> !                 return 0;
> !             }
> !         }
> !
> !         /* pqSendSome was able to send all data. Continue with the next
> !          * chunk of s. */
> !     } /* while */
>
>       return 0;
>   }
> ***************
> *** 575,584 ****
>   }
>
>   /* --------------------------------------------------------------------- */
> ! /* pqFlush: send any data waiting in the output buffer
>    */
>   int
> ! pqFlush(PGconn *conn)
>   {
>       char       *ptr = conn->outBuffer;
>       int            len = conn->outCount;
> --- 594,615 ----
>   }
>
>   /* --------------------------------------------------------------------- */
> ! /* pqSendSome: send any data waiting in the output buffer and return 0
> !  * if all data was sent, -1 if an error occurred or 1 if not all data
> !  * could be written because the socket would have blocked.
> !  *
> !  * For a blocking connection all data will be sent unless an error
> !  * occurrs. -1 will only be returned if the connection is non-blocking.
> !  *
> !  * Internally, the case of data remaining in the buffer after pqSendSome
> !  * could be determined by looking at outCount, but this function also
> !  * serves as the implementation of the new API function PQsendsome.
> !  *
> !  * FIXME: perhaps it would be more useful to return the number of bytes
> !  * remaining?
>    */
>   int
> ! pqSendSome(PGconn *conn)
>   {
>       char       *ptr = conn->outBuffer;
>       int            len = conn->outCount;
> ***************
> *** 586,593 ****
>       if (conn->sock < 0)
>       {
>           printfPQExpBuffer(&conn->errorMessage,
> !                           "pqFlush() -- connection not open\n");
> !         return EOF;
>       }
>
>       /*
> --- 617,624 ----
>       if (conn->sock < 0)
>       {
>           printfPQExpBuffer(&conn->errorMessage,
> !                           "pqSendSome() -- connection not open\n");
> !         return -1;
>       }
>
>       /*
> ***************
> *** 645,651 ****
>                   case ECONNRESET:
>   #endif
>                       printfPQExpBuffer(&conn->errorMessage,
> !                                       "pqFlush() -- backend closed the channel unexpectedly.\n"
>                                         "\tThis probably means the backend terminated abnormally"
>                              " before or while processing the request.\n");
>
> --- 676,682 ----
>                   case ECONNRESET:
>   #endif
>                       printfPQExpBuffer(&conn->errorMessage,
> !                                       "pqSendSome() -- backend closed the channel unexpectedly.\n"
>                                         "\tThis probably means the backend terminated abnormally"
>                              " before or while processing the request.\n");
>
> ***************
> *** 657,670 ****
>                        * the socket open until pqReadData finds no more data
>                        * can be read.
>                        */
> !                     return EOF;
>
>                   default:
>                       printfPQExpBuffer(&conn->errorMessage,
> !                       "pqFlush() --  couldn't send data: errno=%d\n%s\n",
>                                         errno, strerror(errno));
>                       /* We don't assume it's a fatal error... */
> !                     return EOF;
>               }
>           }
>           else
> --- 688,701 ----
>                        * the socket open until pqReadData finds no more data
>                        * can be read.
>                        */
> !                     return -1;
>
>                   default:
>                       printfPQExpBuffer(&conn->errorMessage,
> !                       "pqSendSome() --  couldn't send data: errno=%d\n%s\n",
>                                         errno, strerror(errno));
>                       /* We don't assume it's a fatal error... */
> !                     return -1;
>               }
>           }
>           else
> ***************
> *** 679,685 ****
>
>               /*
>                * if the socket is in non-blocking mode we may need to abort
> !              * here
>                */
>   #ifdef USE_SSL
>               /* can't do anything for our SSL users yet */
> --- 710,716 ----
>
>               /*
>                * if the socket is in non-blocking mode we may need to abort
> !              * here and return 1 to indicate that data is still pending.
>                */
>   #ifdef USE_SSL
>               /* can't do anything for our SSL users yet */
> ***************
> *** 691,704 ****
>                       /* shift the contents of the buffer */
>                       memmove(conn->outBuffer, ptr, len);
>                       conn->outCount = len;
> !                     return EOF;
>                   }
>   #ifdef USE_SSL
>               }
>   #endif
>
>               if (pqWait(FALSE, TRUE, conn))
> !                 return EOF;
>           }
>       }
>
> --- 722,735 ----
>                       /* shift the contents of the buffer */
>                       memmove(conn->outBuffer, ptr, len);
>                       conn->outCount = len;
> !                     return 1;
>                   }
>   #ifdef USE_SSL
>               }
>   #endif
>
>               if (pqWait(FALSE, TRUE, conn))
> !                 return -1;
>           }
>       }
>
> ***************
> *** 707,712 ****
> --- 738,762 ----
>       if (conn->Pfdebug)
>           fflush(conn->Pfdebug);
>
> +     return 0;
> + }
> +
> +
> + /* --------------------------------------------------------------------- */
> + /* pqFlush: send any data waiting in the output buffer
> +  *
> +  * Implemented in terms of pqSendSome to recreate the old behavior which
> +  * returned 0 if all data was sent or EOF. EOF was sent regardless of
> +  * whether an error occurred or not all data was sent on a non-blocking
> +  * socket.
> +  */
> + int
> + pqFlush(PGconn *conn)
> + {
> +     if (pqSendSome(conn))
> +     {
> +         return EOF;
> +     }
>       return 0;
>   }
>
> diff -rc -x *.o postgresql-7.1.3-orig/src/interfaces/libpq/libpq-fe.h
postgresql-7.1.3/src/interfaces/libpq/libpq-fe.h
> *** postgresql-7.1.3-orig/src/interfaces/libpq/libpq-fe.h    Thu Mar 22 05:01:27 2001
> --- postgresql-7.1.3/src/interfaces/libpq/libpq-fe.h    Tue Jan 22 12:13:17 2002
> ***************
> *** 265,270 ****
> --- 265,273 ----
>
>       /* Force the write buffer to be written (or at least try) */
>       extern int    PQflush(PGconn *conn);
> +     /* Force the write buffer to be written (or at least try)
> +            (better than PQflush) */
> +     extern int    PQsendSome(PGconn *conn);
>
>       /*
>        * "Fast path" interface --- not really recommended for application
> diff -rc -x *.o postgresql-7.1.3-orig/src/interfaces/libpq/libpq-int.h
postgresql-7.1.3/src/interfaces/libpq/libpq-int.h
> *** postgresql-7.1.3-orig/src/interfaces/libpq/libpq-int.h    Thu Mar 22 05:01:27 2001
> --- postgresql-7.1.3/src/interfaces/libpq/libpq-int.h    Tue Jan 22 12:13:17 2002
> ***************
> *** 321,326 ****
> --- 321,327 ----
>   extern int    pqPutInt(int value, size_t bytes, PGconn *conn);
>   extern int    pqReadData(PGconn *conn);
>   extern int    pqFlush(PGconn *conn);
> + extern int    pqSendSome(PGconn *conn);
>   extern int    pqWait(int forRead, int forWrite, PGconn *conn);
>   extern int    pqReadReady(PGconn *conn);
>   extern int    pqWriteReady(PGconn *conn);
>
>
>
> --
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>
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