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An event cascade is a ripple effect in a computer program that can lead to errors. This can be observed in a system that relies on event-driven programming, where triggers fire in response to particular actions. The wrong sequence of events can set off an explosion of triggers which may crash the program, cause data loss, or lead to other problematic issues. Programmers can take some steps to address the possibility of a cascade, depending on the programming language they use.
The phenomenon starts with a single triggering event. The program fires the appropriate response, which creates another event, signaling another trigger. This can turn into a ripple effect where multiple processes start to occur at once. As they occur, the user may not be able to halt the process, because the computer is responding to internal commands from the program and cannot stop unless the user force stops or quits, which can also potentially cause an error.
One example of an event cascade is called a deletion cascade, where a single deletion can set off a series of deletions. This can occur when the computer attempts to make sense of data that no longer seems to work after the deletion. Other cascades can add data, move it around, and change program parameters. The failure may be relatively minor, depending on the type of information involved.
Some event cascades are deliberately programmed, because they may be part of the functions of a program. For example, when a graduate student edits a thesis and deletes a footnote, all the following footnotes would then be out of order. Thus, the student's action triggers an event cascade; the word processing program renumbers the next footnote, which triggers the program to renumber the next, and so forth. This eliminates the need to go through the entire program and fix the footnotes every time one is added or taken away, and is a beneficial event cascade.
In other cases, the cascade is not desirable and can create a problem. One option for a programmer is to limit the number of event handlers that can be active at any given time. This gives the program room to manage multiple events at once, but can curb a cascade as it begins. Programs may also be prompted to issue warnings or errors to users when their actions could trigger an event cascade, or the program could automatically stop if it senses data loss.