Description

CommandQueue maintains a queue of Command's, and will go through this queue and execute them when requested. The queue is first-in first-out. This object also has the ability to log commands to a file.

There is one global instance of this class in VMD, called commandQueue. It is used by all the user interface objects (UIObject classes). Each time a new action is requested by the user or some other part of VMD, a new Command instance is created and added to the CommandQueue. Within the main event loop of VMD, after each UIObject is checked for new events, the commands in the queue are all executed until the queue is empty (since the execution of one command may result in the queuing of a new command, this process continues until the queue is empty). Each time the queue is checked, the following occurs:

• The next Command instance at the top of the queue is fetched to be executed.
• If commands are being logged to a file, the text representation of the command is written to that file.
• The command itself is executed, and the return code (success of the command) is stored.
• After it is executed, each UIObject active at that time (which are stored in the UIList object) are informed about the command, and are given both the pointer to the command, and it's success flag. This is done so that user interfaces can update their visual display or internal state to reflect the fact that something has changed. In this way, even though a single user interface component may do some action, ALL user interface's can know when to update their state to reflect the changes in the program.
• After this, the Command instance is deleted. There is one routine which does this differently, `runcommand' (see below).