Purpose of while(1); statement in C

What purpose does while(1); serve ? I am aware while(1) (no semicolon) loops infinitely and is similar to a spinlock situation. However I do not see where while(1); could be used ?

Sample code

if(!condition)
{ 
  while(1);
}

Note: This is not a case of do-while() or plain while(1).

Please note that all valid statements of the language do not have to serve a purpose. They are valid per the grammar of the language. One can build many similar "useless" statements, such as if (1);. I see such statements as the conjunction of a conditional (if, while, etc.) and the empty statement ; (which is also a valid statement although it obviously serves no specific purpose).

That being said, I encountered while (1); in security code. When the user does something very bad with an embedded device, it can be good to block them from trying anything else. With while (1);, we can unconditionally block a device until an accredited operator manually reboots it.

while(1); can also be part of the implementation of a kernel panic, although a for(;;) {} loop seems to be a more common way of expressing the infinite loop, and there might be a non-empty body (for instance to panic_blink()).

If you dig down to assembly, (this is easier to grasp from an embedded systems point of view, or if you tried to program a bootloader)

you will realize that a while loop is just a jmp instruction ... ie

(pseudo code: starting loop address)
add ax, bx
add ax, cx
cmp ax, dx
jz  (pseudo code: another address location)
jmp (pseudo code: starting loop address)

Lets explain how this works, the processor will keep executing instructions sequentially ... no matter what. So the moment it enters this loop it will add register bx to ax and store in ax, add register cx to ax and store to ax, cmp ax, dx (this means subtract dx from ax) the jz instruction means jump to (another address location) if the zero flag is set (which is a bit in the flag register that will be set if the result of the above subtraction is zero), then jmp to starting loop address (pretty straight forward) and redo the whole thing.

The reason I bothered you with all this assembly is to show you that this would translate in C to

int A,B,C,D;
// initialize to what ever;

while(true)
{
A = A + B;
A = A + C;

if((A-D)==0)
{break;}

}

// if((X-Y)==0){break;} is the 
// cmp ax, dx
// jz  (pseudo code: another address location)

So imagine the senario in assembly if you just had a very long list of instructions that didn't end with a jmp (the while loop) to repeat some section or load a new program or do something ... Eventually the processor will reach the last instruction and then load the following instruction to find nothing (it will then freeze or triple fault or something).

That is exactly why, when you want the program to do nothing until an event is triggered, you have to use a while(1) loop, so that the processor keeps jumping in its place and not reach that empty instruction address. When the event is triggered, it jumps to the event handler instructions address, executes it, clears the interrupt and goes back to your while(1) loop just jumping in its place awaiting further interrupts. Btw the while(1) is called a superloop if you want to read more about it ... Just for whoever that is insanely itching to argue and comment negatively at this point, this is not an assembly tutorial or a lecture or anything. It's just plain English explanation that is as simple as possible, overlooking a lot of underlying details like pointers and stacks and whatnot and at some instance over simplifying things to get a point across. No one is looking for documentation accuracy over here and I know this C code won't compile like this, but this is only for Demo !!