Provided by: libpcl1-dev_1.6-1ubuntu1_amd64 
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 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 >.