PCL(3)							    Portable Coroutine Library							    PCL(3)

NAME

       co_create, co_call, co_resume, co_delete, co_exit_to, co_exit, co_current - C coroutine management

SYNOPSIS

       #include <pcl.h>

       coroutine_t co_create(void *func, void *data, void *stack, int stacksize);
       void co_delete(coroutine_t co);
       void co_call(coroutine_t co);
       void co_resume(void);
       void co_exit_to(coroutine_t co);
       void co_exit(void);
       coroutine_t co_current(void);

DESCRIPTION

       The Portable Coroutine Library (PCL) implements the low level functionality for coroutines. For a definition of the term coroutine see The
       Art of Computer Programming by Donald E. Knuth.	Coroutines are a very simple cooperative multitasking environment where the switch from
       one task to another is done explicitly by a function call.  Coroutines are a lot faster than processes or threads switch, since there is no
       OS kernel involvement for the operation. This document defines an API for the low level handling of coroutines i.e. creating and deleting
       coroutines and switching between them.  Higher level functionality (scheduler, etc.) is not covered.

   Functions
       The following functions are defined:

       coroutine_t co_create(void *func, void *data, void *stack, int stacksize);

	      This function creates a new coroutine.  func is the entry point of the coroutine.  It will be called with one arg, a void *, which
	      holds the data passed through the data parameter. If func terminates, the associated coroutine is deleted.  stack is the base of the
	      stack this coroutine will use and stacksize its size in bytes.  You may pass a NULL pointer for stack in which case the memory will
	      be allocated by co_create itself.  Both, stack and stacksize are aligned to system requirements.	A stacksize of less then 4096
	      bytes will be rejected.  You have to make sure, that the stack is large enough for your coroutine and possible signal handlers (see
	      below).  The stack will not grow!  (Exception: the main coroutine uses the standard system stack which may still grow) On success, a
	      handle (coroutine_t) for a new coroutine is returned, otherwise NULL.

       void co_delete(coroutine_t co);

	      This function deletes the given coroutine co.  If the stack for this coroutine was allocated by co_create it will be freed.  After a
	      coroutine handle was passed to co_delete it is invalid and may not be used any more.  It is invalid for a coroutine to delete itself
	      with this function.

       void co_call(coroutine_t co);

	      This function passes execution to the given coroutine co.  The first time the coroutine is executed, its entry point func is called,
	      and the data parameter used during the call to co_create is passed to func.  The current coroutine is suspended until another one
	      restarts it with a co_call or co_resume call. Calling oneself returns immediately.

       void co_resume(void);

	      This function passes execution back to the coroutine which either initially started this one or restarted it after a prior
	      co_resume.

       void co_exit_to(coroutine_t co);

	      This function does the same a co_delete(co_current()) followed by a co_call would do.  That is, it deletes itself and then passes
	      execution to another coroutine co.

       void co_exit(void);

	      This function does the same a co_delete(co_current()) followed by a co_resume would do.  That is, it deletes itself and then passes
	      execution back to the coroutine which either initially started this one or restarted it after a prior co_resume.

       coroutine_t co_current(void);

	      This function returns the currently running coroutine.

   Notes
       Some interactions with other parts of the system are covered here.

       Signals
	      First, a signal handler is not defined to run in any specific coroutine. The only way to leave the signal handler is by a return
	      statement.

	      Second, the signal handler may run with the stack of any coroutine, even with the stack of library internal coroutines which have an
	      undefined stack size (just enough to perform a kernel call).  Using and alternate stack for signal processing (see sigaltstack(2))
	      is recommended!

	      Conclusion: avoid signals like a plague.	The only thing you may do reliable is setting some global variables and return.  Simple
	      kernel calls may work too, but nowadays it's pretty hairy to tell, which function really is a kernel call.  (Btw, all this applies
	      to normal C programs, too.  The coroutines just add one more problem)

       setjmp/longjmp
	      The use of setjmp(2)/longjmp(2) is limited to jumping inside one coroutine.  Never try to jump from one coroutine to another with
	      longjmp(2).

DIAGNOSTICS

       Some fatal errors are caught by the library.  If one occurs, a short message is written to file descriptor 2 (stderr) and a segmentation
       violation is generated.

       [PCL]: Cannot delete itself
	      A coroutine has called co_delete with it's own handle.

       [PCL]: Resume to deleted coroutine
	      A coroutine has deleted itself with co_exit or co_exit_to and the coroutine that was activated by the exit tried a co_resume.

       [PCL]: Stale coroutine called
	      Someone tried to active a coroutine that has already been deleted.  This error is only detected, if the stack of the deleted corou-
	      tine is still resident in memory.

       [PCL]: Context switch failed
	      Low level error generated by the library in case a context switch between two coroutines failes.

SEE ALSO

       Original coroutine library at http://www.goron.de/~froese/coro/coro.html .  GNU Pth library at http://www.gnu.org/software/pth/ .

AUTHOR

       Developed by Davide Libenzi < davidel@xmailserver.org >.  Ideas and man page base source taken by the coroutine library developed by E.
       Toernig < froese@gmx.de >.  Also some code and ideas comes from the GNU Pth library available at http://www.gnu.org/software/pth/ .

BUGS

       There are no known bugs.  But, this library is still in development even if it results very stable and pretty much ready for production
       use.

       Bug reports and comments to Davide Libenzi < davidel@xmailserver.org >.

GNU
									1.6								    PCL(3)