1TRAMPOLINE(3)              Library Functions Manual              TRAMPOLINE(3)
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NAME

6       trampoline - closures as first-class C functions
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SYNOPSIS

9       #include <trampoline.h>
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11       function = alloc_trampoline(address, variable, data);
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13       free_trampoline(function);
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15       is_trampoline(function)
16       trampoline_address(function)
17       trampoline_variable(function)
18       trampoline_data(function)
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DESCRIPTION

21       These  functions implement closures as first-class C functions.  A clo‐
22       sure consists of a regular C function and a piece of  data  which  gets
23       passed to the C function when the closure is called.
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25       Closures as first-class C functions means that they fit into a function
26       pointer and can be called exactly like any other C function.   function
27       =  alloc_trampoline(address,  variable, data) allocates a closure. When
28       function gets called, it stores data in the variable variable and calls
29       the  C function at address.  The function at address is responsible for
30       fetching data out of variable  immediately,  before  execution  of  any
31       other function call.
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33       This  is  much  like gcc's local functions, except that the GNU C local
34       functions have dynamic extent (i.e. are deallocated when  the  creating
35       function  returns), while trampoline provides functions with indefinite
36       extent: function is only deallocated when free_trampoline(function)  is
37       called.
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39       is_trampoline(function) checks whether the C function function was pro‐
40       duced by a call to alloc_trampoline.  If this returns true,  the  argu‐
41       ments given to alloc_trampoline can be retrieved:
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43           trampoline_address(function) returns address,
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45           trampoline_variable(function) returns variable,
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47           trampoline_data(function) returns data.
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SEE ALSO

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

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

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

66       Bruno Haible <bruno@clisp.org>
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ACKNOWLEDGEMENTS

70       Many ideas were cribbed from the gcc source.
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75                                25 October 1997                  TRAMPOLINE(3)
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