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)