PCL(3)                    Portable Coroutine Library                    PCL(3)



NAME
       co_create, co_call, co_resume, co_delete, co_exit_to, co_exit, co_cur-
       rent - 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 function-
       ality 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 corou-
       tines and switching between them.  Higher level functionality (sched-
       uler, etc.) is not covered.


   Functions
       The following functions are defined:

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

              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 pos-
              sible 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. Call-
              ing 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 corou-
              tine, 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 coroutine 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                                   1.2                               PCL(3)
