The Space-Time view displays the activities of individual PVM tasks that are running on the virtual machine. Listed on the left-hand side of the view are the executable names of the tasks, preceded by the host they are running on. The task list is sorted by host so that it is easy to see whether tasks are being clumped on one host. This list also shows the task-to-host mappings (which are not available in the Network view).
The Space-Time view combines three different displays. The first is like a Gantt chart . Beside each listed task is a horizontal bar stretching out in the ``time'' direction. The color of this bar at any time indicates the state of the task. Green indicates that user computations are being executed. Yellow marks the times when the task is executing PVM routines. White indicates when a task is waiting for messages. The bar begins at the time when the task starts executing and ends when the task exits normally. The specific colors used in each case are user customizable.
The second display overlays the first display with the communication activity among tasks. When a message is sent between two tasks, a red line is drawn starting at the sending task's bar at the time the message is sent and ending at the receiving task's bar when the message is received. Note that this is not necessarily the time the message arrived, but rather the time the task returns from pvm_recv(). Visually, the patterns and slopes of the red lines combined with white ``waiting'' regions reveal a lot about the communication efficiency of an application.
The third display appears only when a user clicks on interesting features of the Space-Time view with the left mouse button. A small ``pop-up'' window appears giving detailed information regarding specific task states or messages. If a task bar is clicked on, the state begin and end times are displayed, along with the last PVM system call information. If a message line is clicked on, the window displays the send and receive time as well as the number of bytes in the message and the message tag.
When the mouse is moved inside the Space-Time view, a blue vertical line tracks the cursor and the time corresponding to this vertical line is displayed as Query time at the bottom of the display. This vertical line also appears in the other ``something vs. time'' views so the user can correlate a feature in one view with information given in another view.
The user can zoom into any area of the Space-Time view by dragging the vertical line with the middle mouse button. The view will unzoom back one level when the right mouse button is clicked. It is often the case that very fine communication or waiting states are only visible when the view is magnified with the zoom feature. As with the Query time, the other views also zoom along with the Space-Time view.