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<TITLE> TRAMPOLINE manual page </TITLE>
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<H1>TRAMPOLINE manual page</H1>
<UL>
<LI> <A HREF="#Name">Name</A>
<LI> <A HREF="#Synopsis">Synopsis</A>
<LI> <A HREF="#Description">Description</A>
<LI> <A HREF="#See also">See also</A>
<LI> <A HREF="#Bugs">Bugs</A>
<LI> <A HREF="#Porting">Porting</A>
<LI> <A HREF="#Author">Author</A>
<LI> <A HREF="#Acknowledgements">Acknowledgements</A>
</UL>
<P>
<HR>
<A NAME="Name">
<H2>Name</H2>
</A>
trampoline - closures as first-class C functions
<A NAME="Synopsis">
<H2>Synopsis</H2>
</A>
<PRE>
<CODE>#include <trampoline.h></CODE>
<CODE><VAR>function</VAR> = alloc_trampoline(<VAR>address</VAR>, <VAR>variable</VAR>, <VAR>data</VAR>);</CODE>
<CODE>free_trampoline(<VAR>function</VAR>);</CODE>
<CODE>is_trampoline(<VAR>function</VAR>)</CODE>
<CODE>trampoline_address(<VAR>function</VAR>)</CODE>
<CODE>trampoline_variable(<VAR>function</VAR>)</CODE>
<CODE>trampoline_data(<VAR>function</VAR>)</CODE>
</PRE>
<A NAME="Description">
<H2>Description</H2>
</A>
These functions implement <EM>closures</EM> 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.
<P>
Closures as <EM>first-class C functions</EM> means that they fit
into a function pointer and can be called exactly like any
other C function.
<CODE><VAR>function</VAR> = alloc_trampoline(<VAR>address</VAR>, <VAR>variable</VAR>, <VAR>data</VAR>)</CODE>
allocates a closure.
When <VAR>function</VAR> gets called, it stores
<VAR>data</VAR> in the variable <VAR>variable</VAR>
and calls the C function at <VAR>address</VAR>.
The function at <VAR>address</VAR> is responsible for
fetching <VAR>data</VAR> out of <VAR>variable</VAR>
immediately, before execution of any other function call.
<P>
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 <EM>trampoline</EM>
provides functions with indefinite extent: <CODE><VAR>function</VAR></CODE>
is only deallocated when <CODE>free_trampoline(<VAR>function</VAR>)</CODE> is
called.
<P>
<CODE>is_trampoline(<VAR>function</VAR>)</CODE>
checks whether the C function <CODE><VAR>function</VAR></CODE>
was produced by a call to <CODE>alloc_trampoline</CODE>.
If this returns true, the arguments given to <CODE>alloc_trampoline</CODE>
can be retrieved:
<UL>
<LI> <CODE>trampoline_address(<VAR>function</VAR>)</CODE> returns <VAR>address</VAR>,
<LI> <CODE>trampoline_variable(<VAR>function</VAR>)</CODE> returns <VAR>variable</VAR>,
<LI> <CODE>trampoline_data(<VAR>function</VAR>)</CODE> returns <VAR>data</VAR>.
</UL>
<A NAME="See also">
<H2>See also</H2>
</A>
<A HREF="gcc(1)"><CODE><B>gcc</B></CODE></A>(1), <A HREF="stdarg(3)"><CODE><B>stdarg</B></CODE></A>(3), <A HREF="callback(3)"><CODE><B>callback</B></CODE></A>(3)
<A NAME="Bugs">
<H2>Bugs</H2>
</A>
Passing the data through a global variable is not reentrant. Don't
call trampoline functions from within signal
handlers. This is fixed in the <A HREF="callback(3)"><CODE><B>callback</B></CODE></A>(3) package.
<A NAME="Porting">
<H2>Porting</H2>
</A>
The way gcc builds local functions is described in the gcc
source, file <SAMP>gcc-2.6.3/config/<VAR>cpu</VAR>/<VAR>cpu</VAR>.h</SAMP>.
<A NAME="Author">
<H2>Author</H2>
</A>
Bruno Haible <bruno@clisp.org>
<A NAME="Acknowledgements">
<H2>Acknowledgements</H2>
</A>
Many ideas were cribbed from the gcc source.
<P>
<HR>
<ADDRESS>TRAMPOLINE manual page<BR>
Bruno Haible <bruno@clisp.org>
</ADDRESS>
<P>
Last modified: 1 January 2017.
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