What causes a program to freeze

From what experience I have programming whenever a program has a problem it crashes, whether it is from an unhanded exception or a piece of code that should have been checked for errors, but was not and threw one. What would cause a program to completely freeze a system to the point of requiring a restart.

Edit: Thanks for the answers. As for the language and OS this question was inspired by me playing Fallout and the game freezing twice in an hour causing me to have to rest开发者_运维知识库art the xbox, so I am guessing c++.

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A million different things. The most common that come to mind are:

1. Spawning too many threads or processes, which drowns the OS scheduler.
2. Gobbling too much RAM, which puts the memory manager into page-fault hell.

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In a Dotnet/Java type environment its quite difficult to seize a system up, because the Runtime keeps you code at a distance from the OS.

Closer to the metal say C or C++, Assembly etc you have to play fair with the rest of the system - If you dont have it already grab a copy of Petzold and observe/experiment yourself with the amount of 'boilerplate' code to get a single Window running...

Even closer, down at the driver level all sorts of things can happen...

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There are number of reasons, being internal or external that leads to deadlocked application, more general case is when something is being asked for by a program but is not given that leads to infinite waiting, the practical example to this is, a program writes some text to a file, but when it is about to open a file for writing, same file is opened by any other application, so the requesting app will wait (freeze in some cases if not coded properly) until it gets exclusive control of the file.

And a critical freeze that leads to restarting the system is when the file which is asked for is something which very important for the OS. However, you may not need to restart the system in order to get it back to normal, unless the program which was frozen is written in a language that produces native binary, i.e. C/C++ to be precise. So if application is written in a language which works with the concept of managed code, like any .NET language, it will not need a system restart to get things back to normal.

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page faults, trying to access inaccessible data or memory(acces violation), incompatible data types etc.