(转)不一般的软件bug

Heisenbugs

A heisenbug is a computer bug that disappears or alters its characteristics when it is researched.

One common example is a bug that occurs in a release-mode compile of a program, but not when researched under debug-mode; another is a bug caused by a race condition. The name "heisenbug" is a pun on the "Heisenberg uncertainty principle," a quantum physics term which is commonly (yet inaccurately) used to refer to the way in which observers affect the measurements of the things that they are observing, by the act of observing alone (this is actually the observer effect, and is commonly confused with the Heisenberg uncertainty principle).

One common reason for heisenbug-like behaviour is that executing a program in debug mode often cleans memory before the program starts, and forces variables onto stack locations, instead of keeping them in registers. Another reason is that debuggers commonly provide watches or other user interfaces that cause code (such as property accessors) to be executed, which can, in turn, change the state of the program. Yet another reason is a fandango on core, the effect of a pointer running out of bounds. In C++, many heisenbugs are caused by uninitialized variables.

In an interview Bruce Lindsay tells of being there when the term was first used, and that it was created because Heisenberg said, "The more closely you look at one thing, the less closely can you see something else."^[1]

This claim of origin is almost certainly wrong, as the term has been used for over two decades. For example, the earliest Google-archived mention is from the mailing list (later Usenet news group) comp.risks, moderated by Peter G. Neumann. In RISKS Digest Volume 4 : Issue 34, dated 23 December 1986^[2], Zhahai Stewart contributes an item titled "Another heisenbug" noting that many such contributions have appeared in recent issues of RISKS Digest. The term, and especially the distinction Heisenbug/Bohrbug was already mentioned in 1985 by Jim Gray in an often cited paper about software failures (http://citeseer.ist.psu.edu/gray85why.html).

Bohrbug

A Bohr bug or bohrbug (named after the Bohr atom model) is a bug that manifests reliably under a well-defined (but possibly unknown) set of conditions. Thus, in contrast with heisenbugs, a bohrbug does not disappear or alter its characteristics when it is researched. These include the easiest bugs to fix (where the nature of the problem is obvious), but also bugs that are hard to find and fix and remain in the software during the operational phase.

Mandelbugs

A mandelbug (named after fractal innovator Benoît Mandelbrot) is a computer bug whose causes are so complex that its behavior appears chaotic. This word also implies that the speaker thinks it is a bohrbug rather than a heisenbug.

Some use mandelbug to describe a bug whose behavior does not appear chaotic, but whose causes are so complex that there is no practical solution. An example of this is a bug caused by a flaw in the fundamental design of the entire system.

In the literature, there are inconsistent statements about the relationships between bohrbug, heisenbug, and mandelbug: According to the above definition, mandelbugs are bohrbugs. Heisenbug and bohrbug are considered antonyms. Moreover, it is claimed that all heisenbugs are mandelbugs.

In a recent column in IEEE Computer ^[3], mandelbug is considered the complementary antonym to bohrbug; i.e., a software bug is either a bohrbug or a mandelbug. The apparently complex behavior of a mandelbug is assumed to be caused either by long delays between fault activation and the failure occurrence, or by influences of other software system elements (hardware, operating system, other applications) on the fault's behavior. Heisenbugs (whose behavior is influenced by a debugger, or other means of investigating the fault) are mandelbugs.

Schroedinbugs

A schroedinbug is a bug that manifests only after someone reading source code or using the program in an unusual way notices that it never should have worked in the first place, at which point the program promptly stops working for everybody until fixed. The Jargon File adds: "Though... this sounds impossible, it happens; some programs have harbored latent schroedinbugs for years."

The name schroedinbug is derived from the Schrödinger's cat thought experiment. A well written program executing in a reliable computing environment is expected to follow the principle of determinism, and as such the quantum questions of observability (i.e. breaking the program by reading the source code) posited by Schrödinger (i.e. killing the cat by opening the box) cannot actually affect the operation of a program.

Repairing an obviously defective piece of code is often more important than determining what arcane set of circumstances caused it to work at all (or appear to work) in the first place, and why it then stopped. Because of this, many of these bugs are never fully understood. When bugs of this type are examined in enough detail, they can usually be reclassified as a Bohrbug, Heisenbug, or Mandelbug.

Stotle