Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!eagle.wesleyan.edu!rcook
From: rcook@eagle.wesleyan.edu
Newsgroups: comp.sys.mac.programmer
Subject: asynchronous question
Message-ID: <1990Nov19.130139.35978@eagle.wesleyan.edu>
Date: 19 Nov 90 18:01:38 GMT
Organization: Wesleyan University Computing Center
Lines: 36

Suppose I am making two asynchronous AppleTalk (or Device Manager, for that
matter) like this:

var
  MyParmBlock: ParmBlkPtr;
  async: boolean;

begin
  ...
  async := true; { make the calls asynchronously }
  MyParmBlk := ParmBlkPtr(NewPtr(sizeof(ParmBlkPtr)));

  with MyParmBlock^ do
    begin
      { fill in data }
    end;
  err := SomeAppleTalkCall(MyParmBlock,async);

  with MyParmBlock^ do
    begin
      { fill in some more data }
    end;
  err := SomeOtherAppleTalkCall(MyParmBlock,async);
  ...
end;

Assuming the first AppleTalk call has not yet been completed by the time the
second call is made, is it safe to reuse MyParmBlock in this way?  Ignore for
now the fact that I can't go back and check if the first call was completed
successfully.  In other words, when something is placed in an I/O queue, is a
copy of the parameter block made or is a pointer to your data placed in the
queue instead?  I assume it makes a copy, but I want to hear this from someone
who knows for sure.  Thanks.

Randall Cook
rcook@eagle.wesleyan.edu