1PCL(3) Portable Coroutine Library PCL(3)
2
6 co_thread_init, co_thread_cleanup, co_create, co_call, co_resume,
7 co_delete, co_exit_to, co_exit, co_current, co_get_data, co_set_data -
8 C coroutine management
9
12 #include <pcl.h>
13 int co_thread_init(void);
15 void co_thread_cleanup(void);
17 coroutine_t co_create(void *func, void *data, void *stack, int stacksize);
18 void co_delete(coroutine_t co);
19 void co_call(coroutine_t co);
20 void co_resume(void);
21 void co_exit_to(coroutine_t co);
22 void co_exit(void);
23 coroutine_t co_current(void);
24 void *co_get_data(coroutine_t co);
25 void *co_set_data(coroutine_t co, void *data);
26 Link with -lpthread if you are using a multi-thread version of PCL.
28
30 The Portable Coroutine Library (PCL) implements the low level function‐
31 ality for coroutines. For a definition of the term coroutine see The
32 Art of Computer Programming by Donald E. Knuth. Coroutines are a very
33 simple cooperative multitasking environment where the switch from one
34 task to another is done explicitly by a function call. Coroutines are
35 a lot faster than processes or threads switch, since there is no OS
36 kernel involvement for the operation. This document defines an API for
37 the low level handling of coroutines i.e. creating and deleting corou‐
38 tines and switching between them. Higher level functionality (sched‐
39 uler, etc.) is not covered.
40 Functions
43 The following functions are defined:
44 int co_thread_init(void);
46 If the PCL library is built in multi-thread mode, and if multi
48 threads are actually used, this function should be called before
49 calling any PCL function. If the PCL library is built in multi-
50 thread mode, but it is used only from one thread (the main one,
51 likely), then it is possible to avoid to call co_thread_init().
52 Returns 0 in case of success, or an negative error code in case
53 of error.
54 void co_thread_cleanup(void);
57 If the PCL library is built in multi-thread mode, and if multi
58 threads are actually used, this function should be called before
59 the thread exits, or whenever the thread decides it won't call
60 the PCL functions anymore. A failure in calling
61 co_thread_cleanup() will result in resource leakage by the call‐
62 ing application.
63 coroutine_t co_create(void *func, void *data, void *stack, int stack‐
66 size);
67 This function creates a new coroutine. func is the entry point
69 of the coroutine. It will be called with one arg, a void *,
70 which holds the data passed through the data parameter. If func
71 terminates, the associated coroutine is deleted. stack is the
72 base of the stack this coroutine will use and stacksize its size
73 in bytes. You may pass a NULL pointer for stack in which case
74 the memory will be allocated by co_create itself. Both, stack
75 and stacksize are aligned to system requirements. A stacksize
76 of less then 4096 bytes will be rejected. You have to make
77 sure, that the stack is large enough for your coroutine and pos‐
78 sible signal handlers (see below). The stack will not grow!
79 (Exception: the main coroutine uses the standard system stack
80 which may still grow) On success, a handle (coroutine_t) for a
81 new coroutine is returned, otherwise NULL.
82 void co_delete(coroutine_t co);
85 This function deletes the given coroutine co. If the stack for
87 this coroutine was allocated by co_create it will be freed.
88 After a coroutine handle was passed to co_delete it is invalid
89 and may not be used any more. It is invalid for a coroutine to
90 delete itself with this function.
91 void co_call(coroutine_t co);
94 This function passes execution to the given coroutine co. The
96 first time the coroutine is executed, its entry point func is
97 called, and the data parameter used during the call to co_create
98 is passed to func. The current coroutine is suspended until
99 another one restarts it with a co_call or co_resume call. Call‐
100 ing oneself returns immediately.
101 void co_resume(void);
104 This function passes execution back to the coroutine which
106 either initially started this one or restarted it after a prior
107 co_resume.
108 void co_exit_to(coroutine_t co);
111 This function does the same a co_delete(co_current()) followed
113 by a co_call would do. That is, it deletes itself and then
114 passes execution to another coroutine co.
115 void co_exit(void);
118 This function does the same a co_delete(co_current()) followed
120 by a co_resume would do. That is, it deletes itself and then
121 passes execution back to the coroutine which either initially
122 started this one or restarted it after a prior co_resume.
123 coroutine_t co_current(void);
126 This function returns the currently running coroutine.
128 void *co_get_data(coroutine_t co);
131 This function returns the data associated with the co
133 coroutine. The data associated with a coroutine is the data
134 parameter passed to co_create().
135 void *co_set_data(coroutine_t co, void *data);
138 Sets the data associated with the co coroutine, and returns the
140 previously associated data.
141 Notes
144 Some interactions with other parts of the system are covered here.
145 Threads
147 If the PCL library has been built in multi-thread mode, then it
148 is possible to use it in multi-thread software. A thread should
149 call co_thread_init() before using the PCL APIs, and call
150 co_thread_cleanup() before exiting, or when it has done using
151 the PCL APIs.
152 WARNING: For no reason should two different threads run the same
153 coroutine at the same time.
154 Signals
157 First, a signal handler is not defined to run in any specific
158 coroutine. The only way to leave the signal handler is by a
159 return statement.
160 Second, the signal handler may run with the stack of any corou‐
162 tine, even with the stack of library internal coroutines which
163 have an undefined stack size (just enough to perform a kernel
164 call). Using and alternate stack for signal processing (see
165 sigaltstack(2)) is recommended!
166 Conclusion: avoid signals like a plague. The only thing you may
168 do reliable is setting some global variables and return. Simple
169 kernel calls may work too, but nowadays it's pretty hairy to
170 tell, which function really is a kernel call. (Btw, all this
171 applies to normal C programs, too. The coroutines just add one
172 more problem)
173 setjmp/longjmp
175 The use of setjmp(2)/longjmp(2) is limited to jumping inside one
176 coroutine. Never try to jump from one coroutine to another with
177 longjmp(2).
178
181 Some fatal errors are caught by the library. If one occurs, a short
182 message is written to file descriptor 2 (stderr) and a segmentation
183 violation is generated.
184 [PCL]: Cannot delete itself
186 A coroutine has called co_delete with it's own handle.
187 [PCL]: Resume to deleted coroutine
189 A coroutine has deleted itself with co_exit or co_exit_to and
190 the coroutine that was activated by the exit tried a co_resume.
191 [PCL]: Stale coroutine called
193 Someone tried to active a coroutine that has already been
194 deleted. This error is only detected, if the stack of the
195 deleted coroutine is still resident in memory.
196 [PCL]: Context switch failed
198 Low level error generated by the library in case a context
199 switch between two coroutines failes.
200
203 Original coroutine library at
204 http://www.goron.de/~froese/coro/coro.html . GNU Pth library at
205 http://www.gnu.org/software/pth/ .
206
209 Developed by Davide Libenzi < davidel@xmailserver.org >.
210 Ideas and man page base source taken by the coroutine library developed
211 by E. Toernig < froese@gmx.de >.
212 Also some code and ideas comes from the GNU Pth library available at
213 http://www.gnu.org/software/pth/ .
214
217 There are no known bugs. But, this library is still in development
218 even if it results very stable and pretty much ready for production
219 use.
220 Bug reports and comments to Davide Libenzi < davidel@xmailserver.org >.
222GNU 1.12 PCL(3)