What is a "tight loop"?

Question

I've heard that phrase a lot. What does it mean?

An example would help.

Answer 1

According to Webster's dictionary, "A loop of code that executes without releasing any resources to other programs or the operating system."

http://www.websters-online-dictionary.org/ti/tight+loop.html

Answer 2

From Wiktionary:

1. (computing) In assembly languages, a loop which contains few instructions and iterates many times.
2. (computing) Such a loop which heavily uses I/O or processing resources, failing to adequately share them with other programs running in the operating system.

For case 1 it is probably like

for (unsigned int i = 0; i < 0xffffffff; ++ i) {}

Answer 3

I think the phrase is generally used to designate a loop which iterates many times, and which can have a serious effect on the program's performance - that is, it can use a lot of CPU cycles. Usually you would hear this phrase in a discussion of optimization.

For examples, I think of gaming, where a loop might need to process every pixel on the screen, or scientific app, where a loop is processing entries in giant arrays of data points.

Answer 4

There's a good example of a tight loop (~ infinite loop) in the video Jon Skeet and Tony the Pony.

The example is:

while(text.IndexOf("  ") != -1) text = text.Replace("  ", " ");

which produces a tight loop because IndexOf ignores a Unicode zero-width character (thus finds two adjacent spaces) but Replace does not ignore them (thus not replacing any adjacent spaces).

There are already good definitions in the other answers, so I don't mention them again.