B4X

SSH Parallel Remote Commands on a Single Server

Demonstrates running several commands in parallel on one SSH server and collecting each command's output as it finishes. QuickCmdSend starts each command and returns immediately; QuickCmdCheck reports them as they complete.

Background: Because SSH multiplexes channels, several commands can run at once over one authenticated connection — far faster than running them one after another when each involves waiting. Results arrive in completion order rather than the order the commands were started, so the loop keys off the returned channel number. Distinguish the two negative returns carefully: -1 means "still working, ask again," while -2 means nothing remains to collect or the connection failed.

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Dim success As Boolean = False

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

'  Demonstrates running several commands in parallel on a single SSH server and collecting each
'  command's output as it finishes.

Dim ssh As ChilkatSsh
ssh.Initialize("ssh")

Dim port As Int = 22
success = ssh.Connect("ssh.example.com", port)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


'  Normally you would not hard-code the password in source.  You should instead obtain it
'  from an interactive prompt, environment variable, or a secrets vault.
Dim password As String = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin", password)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


'  QuickCmdSend starts a command and returns immediately, so all three run concurrently, each on
'  its own session channel.
Dim channel1 As Int = ssh.QuickCmdSend("df")
If channel1 < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


Dim channel2 As Int = ssh.QuickCmdSend("date")
If channel2 < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


Dim channel3 As Int = ssh.QuickCmdSend("echo hello world")
If channel3 < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


'  Collect the results.  QuickCmdCheck returns the channel number of a completed command,
'  -1 when commands are still pending but none finished within the timeout, or -2 when nothing
'  remains to be checked (or an error occurred).
Dim pollTimeoutMs As Int = 50
Dim numFinished As Int = 0
Do While numFinished < 3
    Dim channel As Int = ssh.QuickCmdCheck(pollTimeoutMs)
    If channel = -2 Then
        Log(ssh.LastErrorText)
        Return
    End If


    If channel >= 0 Then
        Log("---- channel " & channel & " finished ----")
        Dim cmdOutput As String = ssh.GetReceivedText(channel, "utf-8")
        If ssh.LastMethodSuccess = False Then
            Log(ssh.LastErrorText)
            Return
        End If

        Log(cmdOutput)
        numFinished = numFinished + 1
    End If

Loop

ssh.Disconnect