NAME

       trampoline - closures as first-class C functions

SYNOPSIS

       #include <trampoline.h>

       function = alloc_trampoline(address, variable, data);

       free_trampoline(function);

       is_trampoline(function)
       trampoline_address(function)
       trampoline_variable(function)
       trampoline_data(function)

DESCRIPTION

       These  functions  implement  closures  as  first-class  C  functions.   A closure consists of a regular C
       function and a piece of data which gets passed to the C function when the closure is called.

       Closures as first-class C functions means that they fit into a function pointer and can be called exactly
       like  any  other  C  function.  function = alloc_trampoline(address, variable, data) allocates a closure.
       When function gets called, it stores data in the variable variable and calls the C function  at  address.
       The function at address is responsible for fetching data out of variable immediately, before execution of
       any other function call.

       This is much like gcc's local functions, except that the GNU C local functions have dynamic extent  (i.e.
       are  deallocated when the creating function returns), while trampoline provides functions with indefinite
       extent: function is only deallocated when free_trampoline(function) is called.

       is_trampoline(function)  checks  whether  the  C  function  function  was   produced   by   a   call   to
       alloc_trampoline.  If this returns true, the arguments given to alloc_trampoline can be retrieved:

           trampoline_address(function) returns address,

           trampoline_variable(function) returns variable,

           trampoline_data(function) returns data.

SEE ALSO

       gcc(1), varargs(3), callback(3)

BUGS

       Passing  the data through a global variable is not reentrant. Don't call trampoline functions from within
       signal handlers. This is fixed in the callback(3) package.

PORTING

       The way gcc builds local functions is described in the gcc source, file gcc-2.6.3/config/cpu/cpu.h.

AUTHOR

       Bruno Haible <bruno@clisp.org>

ACKNOWLEDGEMENTS

       Many ideas were cribbed from the gcc source.

                                                 25 October 1997                                   TRAMPOLINE(3)