In computer programming, the word trampoline has a number of meanings, and is generally associated with jump instructions (i.e. moving to different code paths).
Low-level programming
Trampolines (sometimes referred to as indirect jump vectors) are memory locations holding addresses pointing to interrupt service routines, I/O routines, etc. Execution jumps into the trampoline and then immediately jumps out, or bounces, hence the term trampoline. They have many uses:
- Trampoline can be used to overcome the limitations imposed by a central processing unit (CPU) architecture that expects to always find vectors in fixed locations.
- When an operating system is booted on a symmetric multiprocessing (SMP) machine, only one processor, the bootstrap processor, will be active. After the operating system has configured itself, it will instruct the other processors to jump to a piece of trampoline code that will initialize the processors and wait for the operating system to start scheduling threads on them.
High-level programming
- As used in some Lisp implementations, a trampoline is a loop that iteratively invokes thunk-returning functions (continuation-passing style). A single trampoline suffices to express all control transfers of a program; a program so expressed is trampolined, or in trampolined style; converting a program to trampolined style is trampolining. Programmers can use trampolined functions to implement tail-recursive function calls in stack-oriented programming languages.
- When interfacing pieces of code with incompatible calling conventions, a trampoline is used to convert the caller's convention into the callee's convention.
- In embedded systems, trampolines are short snippets of code that start up other snippets of code. For example, rather than write interrupt handlers entirely in assembly language, another option is to write interrupt handlers mostly in C, and use a short trampoline to convert the assembly-language interrupt calling convention into the C calling convention.