TERDS

A Tool for the Easy Realization of Distributed Systems

TERDS is a primitive tool for building distributed systems. The tasks of a TERDS system communicate with and control each other by writing specially formatted commands to their standard output. Tasks receive data from other tasks by reading the data from their standard input. Tasks are identified by integer task IDs, which are used in some commands to identify the target task. The tasks are supervised by a monitor which intercepts all standard output from all tasks, implements control commands, passes on data from communication commands, and provides simple standard input and output facilities for tasks. The user may interact with a distributed system as a priviledged task with task ID 0, by issueing commands from the keyboard and receiving responses on the screen. Tasks may run on any machine on which the user has rsh priviledges (granted in the .rhosts file).

The TERDS software has two components:

The TERDS monitor: This is a perl script that implements the monitor functionality, and provides the user task interface. This script starts the TERDS system.
The TERDS task starter: This is a perl script required for starting new tasks. This script must be available on each machine that will run any tasks, typically made available through NFS.

TERDS requires perl version 5. To start TERDS, execute the TERDS script.

TERDS Commands

Tasks issue TERDS commands by sending them to their standard output, preceded by :::. The monitor understands that any line of standard output starting with ::: is a TERDS command, and will implement the command. The commands are echoed to the user screen (unless supressed as explained below). Lines of output that start with anything other than ::: are considered by the monitor to be normal standard output, and are echoed to the user screen (unless supressed as explained below).

list option

Sends a list of task information to the stnadard intput of the task that output the command. The options are:

all : Lists all tasks. This is the default if the option is omitted.
self : Lists only the task that output the command.
parent : Lists only the parent of the task that output the command.
children : Lists only the children of the task that output the command.

For each task one (long) line is output, being the concatenation of:

:::TaskID=task ID
:::ParentTaskID=parent's task ID
:::HostName=host machine name
:::PID=UNIX PID of the task
:::Program=command line of the program being executed by the task
:::StartedAt=time and date the task was started
:::RunStatus=task status, one of running or suspended
:::TraceStatus=a flag, 0 or 1, indicating whether or not commands output by the task are echoed to the user screen
:::ListenStatus=a flag, 0 or 1, indicating whether or not normal standard output from the task is echoed to the user screen
:::LogStatus=a flag, 0 or 1, indicating whether or not commands and standard output from the task are being logged to a file
:::LogFileName=if commands and standard output are being logged to a file, the name of the file
:::

After the lines for the tasks, a terminating line :::EOF::: is output.

create machine program

Starts a new task on the machine running the program. Depending on local name resolution, the machine may be a simple machine name or may need to be a fully qualified machine name. The program is anything that can be run on the machine, and may include program arguments.

send task ID data

Sends the data to the standard input of the task with the task ID. If the task ID is all then the data is send to the standard input of all tasks (including the priviledged user task 0).

suspend task ID

Suspends the execution of the running task with the task ID. The priviledged user task 0 cannot be suspended. If the task ID is all then all tasks (except the priviledged user task 0) are suspended.

activate task ID

Activates the execution of the suspended task with the task ID. The priviledged user task 0 cannot be activated. If the task ID is all then all tasks (except the priviledged user task 0) are activated.

kill task ID

Kills the execution of the task with the task ID. The priviledged user task 0 cannot be killed. If the task ID is all then all tasks (except the priviledged user task 0) are killed.

trace task ID

Turns on the echo of commands output by the task with the task ID, to the user screen. If the task ID is all then all tasks' commands are echoed. When a task is createed, the echo of commands is initially on.

notrace task ID

Turns off the echo of commands output by the task with the task ID, to the user screen. If the task ID is all then no tasks' commands are echoed.

listen task ID

Turns on the echo of standard output from the task with the task ID, to the user screen. If the task ID is all then all tasks' standard output is echoed. When a task is createed, the echo of standard output is initially on.

nolisten task ID

Turns off the echo of standard output from the task with the task ID, to the user screen. If the task ID is all then no tasks' standard output is echoed.

log task ID file name

Turns on the logging of commands and standard output from the task with the task ID, to the file named file name.

nolog task ID

Turns off the logging of commands and standard output from the task with the task ID, to the file named file name. When a task is createed, the logging of commands and standard output is initially off.

^D

Terminates TERDS. Only the priviledged user task 0 can terminate TERDS.

Example Programs

EchoTask : Echos to standard output anything sent to its standard input, until stop is sent.
FindParentTask : Gets and outputs the task information for its parent.
SleepyTask : Takes a single integer argument, and writes three lines of standard output every argument seconds.
SuicideTask : Sleeps for 3 seconds, then outputs a kill all command and waits to die.
PingTask and PongTask : The PingTask outputs a command to create the PongTask, uses list commands to get its own and the PongTask's task IDs, then repeated sends ping and its own task ID to the PongTask. The PongTask receives the ping and task ID, and sends a pong back to the PingTask. After 10 pings, the PongTask sends pong end back, which stops the PingTask.

Sample Runs

Input from the user is emphsized.

Run using EchoTask

geoff@gettysburg:TERDS> TERDS
:::create gettysburg /home/escambia/geoff/perl/TERDS/EchoTask
ALERT: Task 1 has started
:::list
:::TaskID=0:::ParentTaskID=-1:::HostName=gettysburg:::PID=17729:::Program=user::
:StartedAt=Thu Apr  6 11:05:17 EDT 2000:::RunStatus=running:::TraceStatus=0:::Li
stenStatus=1:::LogStatus=0:::LogFileName=none:::
:::TaskID=1:::ParentTaskID=0:::HostName=gettysburg:::PID=17741:::Program=/home/e
scambia/geoff/perl/TERDS/EchoTask:::StartedAt=Thu Apr  6 11:05:20 EDT 2000:::Run
Status=running:::TraceStatus=1:::ListenStatus=1:::LogStatus=0:::LogFileName=none
:::
:::EOF:::
:::send 1 To the EchoTask
<-   1: To the EchoTask
->   1: 17741 received =To the EchoTask=
:::kill 1
->   1: Killed
ALERT: Task 1 has ended
^D
ALERT: Task 0 has ended
geoff@gettysburg:TERDS>

Run using PingTask and PongTask

geoff@gettysburg:TERDS> TERDS
:::create gettysburg /home/escambia/geoff/perl/TERDS/PingTask
ALERT: Task 2 has started
->   2: Ping about to get its own TaskID
->   2: :::list self
<-   2: :::<-   2: TaskID=2:::<-   2: ParentTaskID=0:::<-   2: HostName=gettysbu
rg:::<-   2: PID=17791:::<-   2: Program=/home/escambia/geoff/perl/TERDS/PingTas
k:::<-   2: StartedAt=Thu Apr  6 11:10:41 EDT 2000:::<-   2: RunStatus=running::
:<-   2: TraceStatus=1:::<-   2: ListenStatus=1:::<-   2: LogStatus=0:::<-   2:
LogFileName=none:::<-   2:
<-   2: :::EOF:::
->   2: Ping self line is :::TaskID=2:::ParentTaskID=0:::HostName=gettysburg:::P
ID=17791:::Program=/home/escambia/geoff/perl/TERDS/PingTask:::StartedAt=Thu Apr
 6 11:10:41 EDT 2000:::RunStatus=running:::TraceStatus=1:::ListenStatus=1:::LogS
tatus=0:::LogFileName=none:::
->   2:
->   2: Ping TaskID is 2
->   2: Ping about to start pong
->   2: :::create gettysburg.cs.miami.edu /home/escambia/geoff/perl/TERDS/PongTa
sk
ALERT: Task 3 has started
->   2: Ping gets pong information
->   2: :::list children
<-   2: :::<-   2: TaskID=3:::<-   2: ParentTaskID=2:::<-   2: HostName=gettysbu
rg.cs.miami.edu:::<-   2: PID=17801:::<-   2: Program=/home/escambia/geoff/perl/
TERDS/PongTask:::<-   2: StartedAt=Thu Apr  6 11:10:47 EDT 2000:::<-   2: RunSta
tus=running:::<-   2: TraceStatus=1:::<-   2: ListenStatus=1:::<-   2: LogStatus
=0:::<-   2: LogFileName=none:::<-   2:
<-   2: :::EOF:::
->   2: Ping children is :::TaskID=3:::ParentTaskID=2:::HostName=gettysburg.cs.m
iami.edu:::PID=17801:::Program=/home/escambia/geoff/perl/TERDS/PongTask:::Starte
dAt=Thu Apr  6 11:10:47 EDT 2000:::RunStatus=running:::TraceStatus=1:::ListenSta
tus=1:::LogStatus=0:::LogFileName=none:::
->   2:
->   2: Pong task is is 3
->   2: Ping is sending a pong in 1 second
->   3: Pong is waiting for a ping
->   2: :::send 3 ping 2
<-   3: ping 2
->   3: Pong got a ping line =ping 2=
->   2: Ping is waiting for a pong
->   3: Pong will reply to 2 in 1 second
->   3: :::send 2 pong
<-   2: pong
->   2: Ping got a pong
  <some output omitted>
->   2: Ping is sending a pong in 1 second
->   3: Pong is waiting for a ping
->   2: :::send 3 ping 2
<-   3: ping 2
->   3: Pong got a ping line =ping 2=
->   2: Ping is waiting for a pong
->   3: Pong will reply to 2 in 1 second
->   3: :::send 2 pong end
<-   2: pong end
ALERT: Task 3 has ended
->   2: Ping got a pong
ALERT: Task 2 has ended
^D
ALERT: Task 0 has ended
geoff@gettysburg:TERDS>