XPVM

XPVM [GKP94] offers both a graphical interface to the PVM console and a means to visualize event traces. The tracing features used by XPVM are based on previous work on Xab, however, they are more flexible. Since PVM 3.3 [BDG+95], tracing is integrated into the PVM library, so there is no need to recompile or re-link the program to be observed. Tracing can be switched on or off at load time, using the PVM console. It is also possible to restrict the set of PVM functions that shall generate trace events. When tracing is enabled, most calls generate two events, one at the beginning and one at the end of the call. Each event contains a time stamp and the parameters or result of the call. Very similar to Xab, events are packed into PVM messages that are sent to the PVM console or to XPVM where they are displayed in the order of arrival.

Just like Xab, XPVM allows to view the trace data either in a continuous play mode or in single steps. However, XPVM provides different, more comfortable views:

• The network view visualizes all hosts currently in the virtual machine by icons showing the host's name and architecture. Different colors are used to show the state of a host. Three states are distinguished: There is no PVM task on this host, at least one task is computing and all tasks are doing communication.

• The space-time view plots the states of all PVM tasks against time. For each task, a color-coded bar is drawn, showing the task's state (computing, communicating, waiting for a message). In addition, messages are visualized as arrows between the corresponding bars.

• The utilization view displays the number of tasks in the three different states over a time axis.

• Finally, a view named call-level-debugger shows the last event traced for each task, together with its parameters.