LOTUSSCRIPT LANGUAGE

How synchronization works
Synchronization involves sharing a single CPU among multiple tasks (or threads) in a way designed to minimize the time required to switch threads. On a thread-enabled server, agents take turns performing their tasks, which saves time and gives the illusion of the tasks occuring at the same time.

This sample agent, Comm1, run at the same time as an identical one named Comm2, illustrates how you can use code locks to synchronize agent execution.

Run concurrently, these agents create a named lock called "Update," then:


The process repeats for the duration of "For loop," in this case, 5 iterations.

'Comm1:

Option   Public

' Remove the following line if you do not have a
' resource library defined.
Use "ThreadsLib"

Sub Initialize
  Dim lockName As String
  Dim lockID As Integer, refcnt As Integer
  Dim gotLock As Variant,  releaseLock As Variant, _
   deleteLock As Variant

   On Error Goto syn_error

   ' Provide some unique name here to distinguish the agents.
  ID = "Comm1  tuvwx:5706 "
  Msgbox  ID & "Started"

   lockName = "Update"
  On Error Goto syn_error

   ' Create the lock
  lockID = Createlock(uName)
  If (lockID <> -1) Then
     Msgbox ID & "Created lock: " & lockID
  End If

   ' Put agent to sleep for a second.  
  ' This gives the second agent time to start.
  Sleep 1

   For x = 1 To 5

      ' Attempt to get the lock and report the outcome
     ' as well as the reference count
     gotLock = CodeLock(lockID)
     If (gotLock) Then  
        Msgbox ID & " Got lock: " & lockID & " - at: " & _
          Now()
        refcnt = Codelockcheck(lockID)
        Msgbox ID & "      Reference count is " & refcnt

         ' Do some meaningful work here, or just sleep
        Sleep 1
     Else
        Msgbox ID & "Failed to get lock"
     End If

      ' Release the lock so the other agent can get it.
     releaseLock = Codeunlock(lockID)
     If (releaseLock) Then
        Msgbox ID & " Releasing lock: " & lockID & _
          " - at: " & Now()

         ' Sleep here allows the other agents to obtain
        ' the lock before this agent has a chance to.
        Sleep 1
     Else
        Msgbox ID & "Failed to release lock"
     End If

   Next

   ' When we are finished, destroy this agent's reference
  ' to the lock
  deleteLock = Destroylock(lockID)
  If (deleteLock ) Then
     Msgbox ID & "Destroyed lock " & lockID
  Else
     Msgbox ID & "Failed to destroy lock"
  End If

   Msgbox  ID & "Done "
  Exit Sub

syn_error:
  errormsg  = "  * * Error: " & Err & " - " &  Error() & _
   " in " & ID & " at " & Erl()
  Msgbox errormsg
  Resume Next

End Sub

A sample output of Comm1 (with an ID of tuvwx:5706) and Comm2 (with an ID of uvwxy:5742) running concurrently as agents through the Domino Web server would look something like the following:

Note Your results will not be identical; due to the nature of asynchronous system locks, you can never predict when specific events will occur.

Addin: Agent message box: Comm1 tuvwx:5706 Started
Addin: Agent message box: Comm1 tuvwx:5706 Created lock: 0
Addin: Agent message box: Comm2 uvwxy:5742 Started
Addin: Agent message box: Comm2 uvwxy:5742 Created lock: 0
Addin: Agent message box: Comm1 tuvwx:5706 Got lock: 0 - at: 2/10/99 1:57:06 PM
Addin: Agent message box: Comm1 tuvwx:5706 Reference count is 1
Addin: Agent message box: Comm2 uvwxy:5742 Got lock: 0 - at: 2/10/99 1:57:07 PM
Addin: Agent message box: Comm2 uvwxy:5742 Reference count is 1
Addin: Agent message box: Comm1 tuvwx:5706 Releasing update_lock: 0 - at: 2/10/99 1:57:07 PM
Addin: Agent message box: Comm2 uvwxy:5742 Releasing update_lock: 0 - at: 2/10/99 1:57:08 PM
Addin: Agent message box: Comm1 tuvwx:5706 Got lock: 0 - at: 2/10/99 1:57:08 PM
Addin: Agent message box: Comm1 tuvwx:5706 Reference count is 1
Addin: Agent message box: Comm2 uvwxy:5742 Got lock: 0 - at: 2/10/99 1:57:09 PM
Addin: Agent message box: Comm2 uvwxy:5742 Reference count is 1
Addin: Agent message box: Comm1 tuvwx:5706 Releasing lock: 0 - at: 2/10/99 1:57:09 PM
Addin: Agent message box: Comm2 uvwxy:5742 Releasing lock: 0 - at: 2/10/99 1:57:10 PM
Addin: Agent message box: Comm1 tuvwx:5706 Got lock: 0 - at: 2/10/99 1:57:10 PM
Addin: Agent message box: Comm1 tuvwx:5706 Reference count is 1
Addin: Agent message box: Comm2 uvwxy:5742 Got lock: 0 - at: 2/10/99 1:57:12 PM
Addin: Agent message box: Comm2 uvwxy:5742 Reference count is 1
Addin: Agent message box: Comm1 tuvwx:5706 Releasing lock: 0 - at: 2/10/99 1:57:12 PM
Addin: Agent message box: Comm2 uvwxy:5742 Releasing lock: 0 - at: 2/10/99 1:57:13 PM
Addin: Agent message box: Comm1 tuvwx:5706 Got lock: 0 - at: 2/10/99 1:57:13 PM
Addin: Agent message box: Comm1 tuvwx:5706 Reference count is 1
Addin: Agent message box: Comm2 uvwxy:5742 Got lock: 0 - at: 2/10/99 1:57:14 PM
Addin: Agent message box: Comm2 uvwxy:5742 Reference count is 1
Addin: Agent message box: Comm1 tuvwx:5706 Releasing lock: 0 - at: 2/10/99 1:57:14 PM
Addin: Agent message box: Comm2 uvwxy:5742 Releasing lock: 0 - at: 2/10/99 1:57:15 PM
Addin: Agent message box: Comm1 tuvwx:5706 Got lock: 0 - at: 2/10/99 1:57:15 PM
Addin: Agent message box: Comm1 tuvwx:5706 Reference count is 1
Addin: Agent message box: Comm2 uvwxy:5742 Got lock: 0 - at: 2/10/99 1:57:16 PM
Addin: Agent message box: Comm2 uvwxy:5742 Reference count is 1
Addin: Agent message box: Comm1 tuvwx:5706 Releasing lock: 0 - at: 2/10/99 1:57:16 PM
Addin: Agent message box: Comm2 uvwxy:5742 Releasing lock: 0 - at: 2/10/99 1:57:18 PM
Addin: Agent message box: Comm1 tuvwx:5706 Destroyed lock 0
Addin: Agent message box: Comm1 tuvwx:5706 Done
Addin: Agent message box: Comm2 uvwxy:5742 Destroyed lock 0
Addin: Agent message box: Comm2 uvwxy:5742 Done

These primitives are used only for communication between instances of cooperating LotusScript agents within a single process. They are designed specifically for asynchronous Web agents.

Supported platforms include Win32, OS/2, UNIX (Solaris, HPUX, AIX), and Alpha-NT.

See Also