In computer programming

Computer programming

Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...

, the word trampoline has a number of meanings, and is generally associated with jumps (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

Interrupt

In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....

 service routines, I/O

I/O

I/O may refer to:* Input/output, a system of communication for information processing systems* Input-output model, an economic model of flow prediction between sectors...

 routines, etc. Execution jumps into the trampoline and then immediately jumps out, or bounces, hence the term trampoline. They have many uses:

CPUs

• Trampoline can be used to overcome the limitations imposed by a CPU
  Central processing unit
  The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
  
   architecture that expects to always find vectors in fixed locations.
• When an operating system
  Operating system
  An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
  
   is booted on an SMP
  Symmetric multiprocessing
  In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
  
   machine, only one processor, the boot-strap 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 which will initialize the processors and wait for the operating system to start scheduling threads on them.

In C and C++

• When interfacing pieces of code with incompatible calling convention
  Calling convention
  In computer science, a calling convention is a scheme for how subroutines receive parameters from their caller and how they return a result; calling conventions can differ in:...
  
  s, a trampoline is used to convert the caller's convention into the callee's convention.
  • In embedded system
    Embedded system
    An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
    
    s, 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.
  • When passing a callback
    Callback (computer science)
    In computer programming, a callback is a reference to executable code, or a piece of executable code, that is passed as an argument to other code. This allows a lower-level software layer to call a subroutine defined in a higher-level layer....
    
     to a system that expects to call a C
    C (programming language)
    C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
    
     function, but one wants it to execute the method function of a particular instance of an object written in C++
    C++
    C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
    
    , one uses a short trampoline to convert the C function-calling convention to the C++ method-calling convention. One method of writing such a trampoline is to use a thunk
    Thunk
    Thunk may refer to:* Thunk , a piece of code to perform a delayed computation * Thunk : a feature of some virtual function table implementations...
    
    . Another method is to use a generic listener.
• In Objective-C
  Objective-C
  Objective-C is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it...
  
  , a trampoline is an object returned by a method that acts like a delegate
  Delegation (programming)
  In object-oriented programming, there are two related notions of delegation.* Most commonly, it refers to a programming language feature making use of the method lookup rules for dispatching so-called self-calls as defined by Lieberman in his 1986 paper "Using Prototypical Objects to Implement...
  
  , "bouncing" a message on to another object.
• In the GCC
  GNU Compiler Collection
  The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
  
   compiler
  Compiler
  A compiler is a computer program that transforms source code written in a programming language into another computer language...
  
  , trampoline refers to a technique for implementing pointers to nested function
  Nested function
  In computer programming, a nested function is a function which is lexically encapsulated within another function. It can only be called by the enclosing function or by functions directly or indirectly nested within the same enclosing function. In other words, the scope of the nested function is...
  
  s. The trampoline is a small piece of code which is constructed on the fly on the stack when the address of a nested function is taken. The trampoline sets up the static link pointer, which allows the nested function to access local variables of the enclosing functions. The function pointer is then simply the address of the trampoline. This avoids having to use "fat" function pointers for nested functions which carry both the code address and the static link.

High Level Programming

• Used in some Lisp implementations, a trampoline is a loop that iteratively invokes thunk
  Thunk
  Thunk may refer to:* Thunk , a piece of code to perform a delayed computation * Thunk : a feature of some virtual function table implementations...
  
  -returning functions (continuation-passing style
  Continuation-passing style
  In functional programming, continuation-passing style is a style of programming in which control is passed explicitly in the form of a continuation. Gerald Jay Sussman and Guy L. Steele, Jr...
  
  ). A single trampoline is sufficient 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. Trampolined functions can be used to implement tail-recursive function calls in stack-oriented programming language
  Stack-oriented programming language
  A stack-oriented programming language is one that relies on a stack machine model for passing parameters. Several programming languages fit this description, notably Forth, RPL, PostScript, and also many Assembly languages ....
  
  s.
• In Java
  Java (programming language)
  Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
  
  , a trampoline refers to using reflection
  Reflection (computer science)
  In computer science, reflection is the process by which a computer program can observe and modify its own structure and behavior at runtime....
  
   to avoid using inner class
  Inner class
  In object-oriented programming , an inner class or nested class is a class declared entirely within the body of another class or interface. It is distinguished from a subclass.-Overview:...
  
  es, for example in event listeners. The time overhead of a reflection call is traded for the space overhead of an inner class. Trampolines in Java usually involve the creation of a GenericListener to pass events to an outer class.

Other Languages

• In the esoteric programming language
  Esoteric programming language
  An esoteric programming language is a programming language designed as a test of the boundaries of computer programming language design, as a proof of concept, or as a joke...
  
   Befunge
  Befunge
  Befunge is a stack-based, reflective, esoteric programming language. It differs from conventional languages in that programs are arranged on a two-dimensional grid...
  
  , a trampoline is an instruction to skip the next cell in the control flow
  Control flow
  In computer science, control flow refers to the order in which the individual statements, instructions, or function calls of an imperative or a declarative program are executed or evaluated....
  
  .