oracle dbms_pipe：消息顺序有时会中断（不是先进先出）

Question

多年以来（2000年之前的夏令时），我们一直使用名为HOSTP的程序包和名为host_d的Pro * C可执行文件来执行PL / SQL中的shell命令。 这两个程序都使用DBMS_PIPE进行通信。

这是HOSTP代码的主要功能：

  FUNCTION hostd (command IN VARCHAR2,
                       hostuser IN VARCHAR2,
                       timeout1 IN NUMBER DEFAULT 300,
                       timeout2 IN NUMBER DEFAULT 1200,
                       timeout3 IN NUMBER DEFAULT 240,
                       maxretry IN NUMBER DEFAULT 12)
  RETURN VARCHAR2 IS

    termiap      VARCHAR2(255);
    status       NUMBER;
    result       VARCHAR2(2000);
    command_code NUMBER;
    pipe_name    VARCHAR2(30);
    m_datei      utl_file.file_type;
    m_dutzend    pls_integer;

                 procedure p_debug (text_i in varchar) is
                 begin
                    m_datei := utl_file.fopen (hostuser || '/log',
                                               'hostd.' || to_char (sysdate, 'yyyymmdd') || '
.log',
                                               'a',
                                               4000);
                    utl_file.put_line (m_datei,
                                       pipe_name || ' ' || to_char (sysdate, 'hh24:mi:ss') ||
 ' ' || text_i);
                    utl_file.fclose (m_datei);
                 exception when others then dbms_output.put_line (sqlerrm);
                                            if utl_file.is_open (m_datei)
                                            then
                                               utl_file.fclose (m_datei);
                                            end if;
                 end p_debug;

  BEGIN
    pipe_name := DBMS_PIPE.UNIQUE_SESSION_NAME;
    DBMS_PIPE.PACK_MESSAGE('HOSTD');
    DBMS_PIPE.PACK_MESSAGE(pipe_name);
    DBMS_PIPE.PACK_MESSAGE(command);
    DBMS_PIPE.PACK_MESSAGE(hostuser);
    status := DBMS_PIPE.SEND_MESSAGE(hostuser || '_pipe', timeout1);
    p_debug ('S ' || status || ' ' || command || ' ' || to_char(timeout1) || ' ' || to_char(t
imeout2) || ' ' || to_char(timeout3) || ' ' || to_char(maxretry));
    IF status <> 0 THEN
      p_debug ('20020');
      termiap := termiap||' hostd-send-error: ' || status;
      termiap := termiap||' hostd-send-error: ' || status;
      RAISE_APPLICATION_ERROR(-20020,
        'hostd: Error while sending.  Status = ' || status);
    END IF;

 m_dutzend := 0;
 loop
    status := DBMS_PIPE.RECEIVE_MESSAGE(pipe_name, timeout3);
    p_debug ('A ' || status);

    -- ACK
    IF status = 0 THEN
       exit;
    else
      m_dutzend := m_dutzend + 1;
      if m_dutzend >= maxretry
      then
         p_debug ('20021 hostd: maxretry reached waiting for ACK');
         termiap := termiap||' hostd-receive-error: ' || status;
         RAISE_APPLICATION_ERROR(-20021,
           'hostd: Too many retries.
            Status = ' || status);
      end if;
    END IF;
 end loop;
    DBMS_PIPE.UNPACK_MESSAGE(result);
    IF result <> 'ACK' THEN
      p_debug ('20022 hostd: ACK not received, but ' || result);
    END IF;

    status := DBMS_PIPE.RECEIVE_MESSAGE(pipe_name, timeout2);

    IF status <> 0 THEN
      p_debug ('20023 hostd: waiting for done returns status ' || status);
      termiap := termiap||' hostd-receive-error: ' || status;
      RAISE_APPLICATION_ERROR(-20023,
        'hostd: Error while receiving.
         Status = ' || status);
    END IF;

    DBMS_PIPE.UNPACK_MESSAGE(result);
    IF result <> 'done' THEN
      p_debug ('R ' || status || ' ' || result || ' 20022');
      RAISE_APPLICATION_ERROR(-20022,
        'hostd: done not received, but ' || result);
      dbms_output.put_line ('20022 hostd: done not received, but ' || result);
      termiap := termiap||' hostd-receive-error: done not received';
    ELSE
      DBMS_PIPE.UNPACK_MESSAGE(command_code);
      DBMS_PIPE.UNPACK_MESSAGE(termiap);
      p_debug ('R ' || status || ' ' || result || ' ' || command_code || ' ' || replace (term
iap, chr (10), null));
      IF command_code <> 0 THEN
        IF (length(termiap)+length(command_code)+16 > 255) THEN
           termiap := substr(termiap, 1, 255 - length(command_code)-16);
        END IF;
        termiap := termiap||' execute-error: '|| command_code;
      END IF;
    END IF;

    RETURN termiap;
  END hostd;

另一端的Host_d是用Pro * C编写的守护程序，用于执行Shell命令并返回结果。 我在这里提供最相关部分的摘要：

EXEC SQL EXECUTE
BEGIN
        :status := DBMS_PIPE.RECEIVE_MESSAGE(:xpipename, :RECEIVE_TIMEOUT);
        IF :status = 0 THEN
                DBMS_PIPE.UNPACK_MESSAGE(:command);
        END IF;
END;
END-EXEC;

....

EXEC SQL EXECUTE
BEGIN
        DBMS_PIPE.UNPACK_MESSAGE(:return_name);
        DBMS_PIPE.UNPACK_MESSAGE(:value);
        DBMS_PIPE.UNPACK_MESSAGE(:hostuid);
        END;
END-EXEC;
EXEC SQL EXECUTE
BEGIN
        DBMS_PIPE.PACK_MESSAGE('ACK');
        :status := DBMS_PIPE.SEND_MESSAGE(:return_name);
END;
END-EXEC;

...

EXEC SQL COMMIT WORK RELEASE;

...（在这里做fork（））

/* reconnect to Oracle as parent & child - can we avoid this as parent? (AR 060207) */
EXEC SQL WHENEVER SQLERROR DO connect_error();
EXEC SQL CONNECT :uid;
EXEC SQL WHENEVER SQLERROR DO sql_error();

...（在孩子中）

EXEC SQL WHENEVER SQLERROR DO sql_error();
EXEC SQL EXECUTE
BEGIN
DBMS_PIPE.PACK_MESSAGE('done');
DBMS_PIPE.PACK_MESSAGE(:exitstat);
DBMS_PIPE.PACK_MESSAGE(:xtermiap);
:status := DBMS_PIPE.SEND_MESSAGE(:return_name);
END;
END-EXEC;
if (status != 0) {
        fprintf (stderr, "[%s] Hostd error while responding to hostd command., %s", tstr(), hostdcom);
        fprintf (stderr, "  status: %d, errno: %d (%s)\n", status, errno, strerror(errno));
}
EXEC SQL COMMIT WORK RELEASE;
exit(0);

大多数请求都是可以的（二十年来，该机制已经以其基本形式大量使用了== 10个应用程序）。

但是有时我们会在HOSTP的日志中得到这个：

root@vmkern $ grep 080DA38D0001 <logfile>
ORA$PIPE$080DA38D0001 13:58:33 S 0 <request> 300 1200 240 12
ORA$PIPE$080DA38D0001 13:58:33 A 0
ORA$PIPE$080DA38D0001 13:58:33 20022 hostd: ACK not received, but done
ORA$PIPE$080DA38D0001 13:58:33 R 0 ACK 20022

将上面的HOSTP代码与该日志进行比较，就好像来自host_d的ACK和DONE消息以错误的顺序发送到HOSTP一样。