243 lines
6.5 KiB
C
243 lines
6.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* libpq-be-fe-helpers.h
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* Helper functions for using libpq in extensions
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*
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* Code built directly into the backend is not allowed to link to libpq
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* directly. Extension code is allowed to use libpq however. However, libpq
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* used in extensions has to be careful to block inside libpq, otherwise
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* interrupts will not be processed, leading to issues like unresolvable
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* deadlocks. Backend code also needs to take care to acquire/release an
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* external fd for the connection, otherwise fd.c's accounting of fd's is
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* broken.
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*
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* This file provides helper functions to make it easier to comply with these
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* rules. It is a header only library as it needs to be linked into each
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* extension using libpq, and it seems too small to be worth adding a
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* dedicated static library for.
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*
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* TODO: For historical reasons the connections established here are not put
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* into non-blocking mode. That can lead to blocking even when only the async
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* libpq functions are used. This should be fixed.
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*
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* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/libpq/libpq-be-fe-helpers.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef LIBPQ_BE_FE_HELPERS_H
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#define LIBPQ_BE_FE_HELPERS_H
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/*
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* Despite the name, BUILDING_DLL is set only when building code directly part
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* of the backend. Which also is where libpq isn't allowed to be
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* used. Obviously this doesn't protect against libpq-fe.h getting included
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* otherwise, but perhaps still protects against a few mistakes...
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*/
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#ifdef BUILDING_DLL
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#error "libpq may not be used code directly built into the backend"
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#endif
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#include "libpq-fe.h"
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#include "miscadmin.h"
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#include "storage/fd.h"
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#include "storage/latch.h"
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#include "utils/wait_event.h"
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static inline void libpqsrv_connect_prepare(void);
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static inline void libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info);
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/*
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* PQconnectdb() wrapper that reserves a file descriptor and processes
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* interrupts during connection establishment.
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*
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* Throws an error if AcquireExternalFD() fails, but does not throw if
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* connection establishment itself fails. Callers need to use PQstatus() to
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* check if connection establishment succeeded.
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*/
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static inline PGconn *
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libpqsrv_connect(const char *conninfo, uint32 wait_event_info)
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{
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PGconn *conn = NULL;
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libpqsrv_connect_prepare();
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conn = PQconnectStart(conninfo);
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libpqsrv_connect_internal(conn, wait_event_info);
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return conn;
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}
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/*
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* Like libpqsrv_connect(), except that this is a wrapper for
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* PQconnectdbParams().
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*/
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static inline PGconn *
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libpqsrv_connect_params(const char *const *keywords,
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const char *const *values,
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int expand_dbname,
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uint32 wait_event_info)
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{
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PGconn *conn = NULL;
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libpqsrv_connect_prepare();
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conn = PQconnectStartParams(keywords, values, expand_dbname);
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libpqsrv_connect_internal(conn, wait_event_info);
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return conn;
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}
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/*
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* PQfinish() wrapper that additionally releases the reserved file descriptor.
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*
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* It is allowed to call this with a NULL pgconn iff NULL was returned by
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* libpqsrv_connect*.
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*/
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static inline void
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libpqsrv_disconnect(PGconn *conn)
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{
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/*
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* If no connection was established, we haven't reserved an FD for it (or
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* already released it). This rule makes it easier to write PG_CATCH()
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* handlers for this facility's users.
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*
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* See also libpqsrv_connect_internal().
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*/
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if (conn == NULL)
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return;
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ReleaseExternalFD();
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PQfinish(conn);
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}
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/* internal helper functions follow */
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/*
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* Helper function for all connection establishment functions.
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*/
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static inline void
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libpqsrv_connect_prepare(void)
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{
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/*
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* We must obey fd.c's limit on non-virtual file descriptors. Assume that
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* a PGconn represents one long-lived FD. (Doing this here also ensures
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* that VFDs are closed if needed to make room.)
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*/
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if (!AcquireExternalFD())
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{
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#ifndef WIN32 /* can't write #if within ereport() macro */
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ereport(ERROR,
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(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
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errmsg("could not establish connection"),
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errdetail("There are too many open files on the local server."),
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errhint("Raise the server's max_files_per_process and/or \"ulimit -n\" limits.")));
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#else
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ereport(ERROR,
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(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
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errmsg("could not establish connection"),
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errdetail("There are too many open files on the local server."),
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errhint("Raise the server's max_files_per_process setting.")));
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#endif
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}
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}
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/*
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* Helper function for all connection establishment functions.
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*/
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static inline void
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libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info)
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{
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/*
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* With conn == NULL libpqsrv_disconnect() wouldn't release the FD. So do
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* that here.
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*/
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if (conn == NULL)
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{
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ReleaseExternalFD();
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return;
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}
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/*
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* Can't wait without a socket. Note that we don't want to close the libpq
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* connection yet, so callers can emit a useful error.
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*/
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if (PQstatus(conn) == CONNECTION_BAD)
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return;
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/*
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* WaitLatchOrSocket() can conceivably fail, handle that case here instead
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* of requiring all callers to do so.
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*/
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PG_TRY();
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{
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PostgresPollingStatusType status;
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/*
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* Poll connection until we have OK or FAILED status.
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*
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* Per spec for PQconnectPoll, first wait till socket is write-ready.
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*/
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status = PGRES_POLLING_WRITING;
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while (status != PGRES_POLLING_OK && status != PGRES_POLLING_FAILED)
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{
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int io_flag;
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int rc;
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if (status == PGRES_POLLING_READING)
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io_flag = WL_SOCKET_READABLE;
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#ifdef WIN32
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/*
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* Windows needs a different test while waiting for
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* connection-made
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*/
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else if (PQstatus(conn) == CONNECTION_STARTED)
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io_flag = WL_SOCKET_CONNECTED;
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#endif
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else
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io_flag = WL_SOCKET_WRITEABLE;
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rc = WaitLatchOrSocket(MyLatch,
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WL_EXIT_ON_PM_DEATH | WL_LATCH_SET | io_flag,
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PQsocket(conn),
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0,
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wait_event_info);
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/* Interrupted? */
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if (rc & WL_LATCH_SET)
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{
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ResetLatch(MyLatch);
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CHECK_FOR_INTERRUPTS();
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}
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/* If socket is ready, advance the libpq state machine */
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if (rc & io_flag)
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status = PQconnectPoll(conn);
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}
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}
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PG_CATCH();
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{
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/*
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* If an error is thrown here, the callers won't call
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* libpqsrv_disconnect() with a conn, so release resources
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* immediately.
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*/
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ReleaseExternalFD();
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PQfinish(conn);
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PG_RE_THROW();
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}
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PG_END_TRY();
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}
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#endif /* LIBPQ_BE_FE_HELPERS_H */
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