Re: Fix for non-blocking connections in libpq

This has been saved for the 7.3 release:

http://candle.pha.pa.us/cgi-bin/pgpatches2

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

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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