trampoline - closures as first-class C functions

       Many ideas were cribbed from the gcc source.

                                                 1 January 2017                                    TRAMPOLINE(3)

       Bruno Haible <bruno@clisp.org>

       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.

       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-classCfunctions 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.

       trampoline - closures as first-class C functions

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

gcc(1), stdarg(3), callback(3)

#include<trampoline.h>function=alloc_trampoline(address,variable,data);free_trampoline(function);is_trampoline(function)trampoline_address(function)trampoline_variable(function)trampoline_data(function)