msgctl

Perform various operations on a message queue

Declaration

Source position: ipc.pp line 659

  function msgctl(msqid: cint; cmd: cint; buf: PMSQid_ds) : cint;

Description

msgctl performs various operations on the message queue with id ID. Which operation is performed, depends on the cmd parameter, which can have one of the following values:

IPC_STAT

In this case, the msgctl call fills the TMSQid_ds structure with information about the message queue.

IPC_SET

in this case, the msgctl call sets the permissions of the queue as specified in the ipc_perm record inside buf.

IPC_RMID

If this is specified, the message queue will be removed from the system.

buf contains the data that are needed by the call. It can be Nil in case the message queue should be removed.

The function returns True if success full, False otherwise.

Errors

On error, False is returned, and IPCerror is set accordingly.

See also

Name	Description
msgget	Return message queue ID, possibly creating the queue
msgrcv	Retrieve a message from the queue
msgsnd	Send a message to the message queue

Example

program msgtool;
Uses ipc,baseunix;
Type
  PMyMsgBuf = ^TMyMsgBuf;
  TMyMsgBuf = record
    mtype : Longint;
    mtext : string[255];
  end;
Procedure DoError (Const Msg : string);
begin
  Writeln (msg,' returned an error : ',fpgeterrno);
  halt(1);
end;
Procedure SendMessage (Id : Longint;
                       Var Buf : TMyMsgBuf;
                       MType : Longint;
                       Const MText : String);
begin
  Writeln ('Sending message.');
  Buf.mtype:=mtype;
  Buf.Mtext:=mtext;
  If  msgsnd(Id,PMsgBuf(@Buf),256,0)=-1 then
    DoError('msgsnd');
end;
Procedure ReadMessage (ID : Longint;
                       Var Buf : TMyMsgBuf;
                       MType : longint);
begin
  Writeln ('Reading message.');
  Buf.MType:=MType;
  If msgrcv(ID,PMSGBuf(@Buf),256,mtype,0)<>-1 then
    Writeln ('Type : ',buf.mtype,' Text : ',buf.mtext)
  else
    DoError ('msgrcv');
end;
Procedure RemoveQueue ( ID : Longint);
begin
  If msgctl (id,IPC_RMID,Nil)<>-1 then
    Writeln ('Removed Queue with id ',Id);
end;
Procedure ChangeQueueMode (ID,mode : longint);
Var QueueDS : TMSQid_ds;
begin
  If  msgctl (Id,IPC_STAT,@QueueDS)=-1 then
    DoError ('msgctl : stat');
  Writeln ('Old permissions : ',QueueDS.msg_perm.mode);
  QueueDS.msg_perm.mode:=Mode;
  if msgctl (ID,IPC_SET,@QueueDS)=0 then
    Writeln ('New permissions : ',QueueDS.msg_perm.mode)
  else
   DoError ('msgctl : IPC_SET');
end;
procedure usage;
begin
  Writeln ('Usage : msgtool s(end)    <type> <text> (max 255 characters)');
  Writeln ('                r(eceive) <type>');
  Writeln ('                d(elete)');
  Writeln ('                m(ode) <decimal mode>');
  halt(1);
end;
Function StrToInt (S : String): longint;
Var M : longint;
    C : Integer;
begin
  val (S,M,C);
  If C<>0 Then DoError ('StrToInt : '+S);
  StrToInt:=M;
end;
Var
  Key : TKey;
  ID  : longint;
  Buf : TMyMsgBuf;
const ipckey = '.'#0;
begin
  If Paramcount<1 then Usage;
  key :=Ftok(@ipckey[1],ord('M'));
  ID:=msgget(key,IPC_CREAT or 438);
  If ID<0 then DoError ('MsgGet');
  Case upCase(Paramstr(1)[1]) of
   'S' : If ParamCount<>3 then
           Usage
         else
           SendMessage (id,Buf,StrToInt(Paramstr(2)),paramstr(3));
   'R' : If ParamCount<>2 then
           Usage
         else
           ReadMessage (id,buf,strtoint(Paramstr(2)));
   'D' : If ParamCount<>1 then
           Usage
         else
           RemoveQueue (ID);
   'M' : If ParamCount<>2 then
           Usage
         else
           ChangeQueueMode (id,strtoint(paramstr(2)));
   else
     Usage
   end;
end.