makecontext(3)             Library Functions Manual             makecontext(3)

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       makecontext, swapcontext - <?><?><?><?><?><?><?><?><?>
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       <?><?><?><?><?> C (libc, -lc)

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       #include <ucontext.h>

       void makecontext(ucontext_t *ucp, void (*func)(), int argc, ...);
       int swapcontext(ucontext_t *restrict oucp,
                       const ucontext_t *restrict ucp);

<?><?><?><?><?><?><?><?>
       In a System V-like environment, one has the type ucontext_t (defined in
       <ucontext.h> and described in getcontext(3))  and the four functions
       getcontext(3), setcontext(3), makecontext(), and swapcontext()  that
       allow user-level context switching between multiple threads of control
       within a process.

       <?><?><?><?><?><?><?> makecontext() <?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?>, <?><?> <?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?> ucp (<?><?><?><?><?><?><?><?><?><?> <?><?>
       <?><?><?><?><?><?> getcontext(3)). <?><?><?><?><?>
       <?><?><?><?><?><?><?> makecontext(), <?><?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?> <?><?><?><?><?><?><?><?> <?><?><?><?><?>
       <?><?><?><?> <?><?><?> <?><?><?><?><?> <?><?><?><?><?><?><?><?><?> <?>
       <?><?><?><?><?><?><?><?><?> <?><?><?> <?><?><?><?><?> ucp->uc_stack,
       <?> <?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?> <?> <?><?><?><?><?><?><?><?><?> <?><?><?>
       <?><?><?><?><?> ucp->uc_link.

       <?><?><?><?><?><?><?>, <?><?><?><?><?> <?><?><?><?>
       <?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?><?><?><?> (<?>
       <?><?><?><?><?><?><?> setcontext(3) <?><?><?> swapcontext()),
       <?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?> func <?> <?><?>
       <?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?><?>
       (int), <?><?><?><?><?><?><?><?><?> <?><?><?><?><?> argc;
       <?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?> <?><?><?><?><?><?><?>
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       <?><?><?><?><?><?><?><?><?><?> <?> argc. <?><?><?><?><?>
       <?><?><?><?><?><?><?><?> <?><?> <?><?><?><?><?><?><?>
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       <?><?><?><?><?><?><?><?>. <?><?><?><?> <?><?><?><?><?><?><?><?><?>
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       <?><?><?><?><?> NULL, <?><?> <?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?><?>.

       <?><?><?><?><?><?><?> swapcontext() <?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?> <?>
       <?><?><?><?><?><?><?><?><?>, <?><?> <?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?> oucp, <?> <?><?><?><?><?> <?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?>, <?><?>
       <?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?> ucp.

<?><?><?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?>
       When successful, swapcontext()  does not return.  (But we may return
       later, in case oucp is activated, in which case it looks like
       swapcontext()  returns 0.)  On error, swapcontext()  returns -1 and
       sets errno to indicate the error.

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       ENOMEM <?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?><?><?><?>
              <?><?><?><?><?><?><?><?><?>
              <?><?><?><?><?><?><?><?><?><?><?><?>.

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       <?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?> <?> attributes(7).

       +----------------------------+----------------------------------------------------------+--------------------------+
       |<?><?><?><?><?><?><?><?><?> | <?><?><?><?><?><?><?>                                    | <?><?><?><?><?><?><?><?> |
       +----------------------------+----------------------------------------------------------+--------------------------+
       |makecontext()               | <?><?><?><?><?><?><?><?><?><?><?><?> <?> <?><?><?><?><?> | MT-Safe race:ucp         |
       +----------------------------+----------------------------------------------------------+--------------------------+
       |swapcontext()               | <?><?><?><?><?><?><?><?><?><?><?><?> <?> <?><?><?><?><?> | MT-Safe race:oucp        |
       |                            |                                                          | race:ucp                 |
       +----------------------------+----------------------------------------------------------+--------------------------+
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       None.

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       glibc 2.1.  SUSv2, POSIX.1-2001.  Removed in POSIX.1-2008, citing
       portability issues, and recommending that applications be rewritten to
       use POSIX threads instead.

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       <?><?><?><?><?><?><?><?><?><?> ucp->uc_stack <?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?> <?> sigaltstack(2), <?>
       <?><?><?><?><?><?>: <?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?> <?><?><?><?><?><?> <?> <?><?><?><?><?><?>
       <?><?><?><?><?><?><?> <?><?><?><?><?><?>, <?><?><?><?><?><?><?>
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       <?><?> <?><?><?><?>, <?>
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       <?><?><?> <?><?><?><?><?><?><?><?><?><?><?>.

       On architectures where int and pointer types are the same size (e.g.,
       x86-32, where both types are 32 bits), you may be able to get away with
       passing pointers as arguments to makecontext()  following argc.
       However, doing this is not guaranteed to be portable, is undefined
       according to the standards, and won't work on architectures where
       pointers are larger than ints.  Nevertheless, starting with glibc 2.8,
       glibc makes some changes to makecontext(), to permit this on some
       64-bit architectures (e.g., x86-64).

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       <?><?><?><?><?><?><?><?><?><?><?><?><?> getcontext(3), makecontext()
       <?> swapcontext(). <?><?><?> <?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?> <?><?><?><?> <?><?><?><?><?><?><?><?><?>:

           $ ./a.out
           main: swapcontext(&uctx_main, &uctx_func2)
           func2: <?><?><?><?><?><?><?><?>
           func2: swapcontext(&uctx_func2, &uctx_func1)
           func1: <?><?><?><?><?><?><?><?>
           func1: swapcontext(&uctx_func1, &uctx_func2)
           func2: <?><?><?><?><?><?><?>
           func1: <?><?><?><?><?><?><?>
           main: <?><?><?><?><?>

   <?><?><?><?><?><?><?><?> <?><?><?> <?><?><?><?><?><?><?><?><?>
       #include <stdio.h>
       #include <stdlib.h>
       #include <ucontext.h>

       static ucontext_t uctx_main, uctx_func1, uctx_func2;

       #define handle_error(msg) \
           do { perror(msg); exit(EXIT_FAILURE); } while (0)

       static void
       func1(void)
       {
           printf("%s: started\n", __func__);
           printf("%s: swapcontext(&uctx_func1, &uctx_func2)\n", __func__);
           if (swapcontext(&uctx_func1, &uctx_func2) == -1)
               handle_error("swapcontext");
           printf("%s: returning\n", __func__);
       }

       static void
       func2(void)
       {
           printf("%s: started\n", __func__);
           printf("%s: swapcontext(&uctx_func2, &uctx_func1)\n", __func__);
           if (swapcontext(&uctx_func2, &uctx_func1) == -1)
               handle_error("swapcontext");
           printf("%s: returning\n", __func__);
       }

       int
       main(int argc, char *argv[])
       {
           char func1_stack[16384];
           char func2_stack[16384];

           if (getcontext(&uctx_func1) == -1)
               handle_error("getcontext");
           uctx_func1.uc_stack.ss_sp = func1_stack;
           uctx_func1.uc_stack.ss_size = sizeof(func1_stack);
           uctx_func1.uc_link = &uctx_main;
           makecontext(&uctx_func1, func1, 0);

           if (getcontext(&uctx_func2) == -1)
               handle_error("getcontext");
           uctx_func2.uc_stack.ss_sp = func2_stack;
           uctx_func2.uc_stack.ss_size = sizeof(func2_stack);
           /* Successor context is f1(), unless argc > 1 */
           uctx_func2.uc_link = (argc > 1) ? NULL : &uctx_func1;
           makecontext(&uctx_func2, func2, 0);

           printf("%s: swapcontext(&uctx_main, &uctx_func2)\n", __func__);
           if (swapcontext(&uctx_main, &uctx_func2) == -1)
               handle_error("swapcontext");

           printf("%s: exiting\n", __func__);
           exit(EXIT_SUCCESS);
       }

<?><?><?><?><?><?><?><?> <?><?><?><?><?>
       sigaction(2), sigaltstack(2), sigprocmask(2), getcontext(3),
       sigsetjmp(3)

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       <?><?><?><?><?><?><?><?><?><?>(<?>) aereiae <aereiae@gmail.com>, Alexey
       <a.chepugov@gmail.com>, Azamat Hackimov <azamat.hackimov@gmail.com>,
       Dmitriy S. Seregin <dseregin@59.ru>, Dmitry Bolkhovskikh
       <d20052005@yandex.ru>, ITriskTI <ITriskTI@gmail.com>, Max Is
       <ismax799@gmail.com>, Yuri Kozlov <yuray@komyakino.ru>, <?><?><?><?>
       <?><?><?><?><?><?> <pavia00@gmail.com> <?> <?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?><?><?>
       <maljanow@outlook.com>

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       <?><?><?><?><?><?><?><?> GNU (GNU General Public License - GPL,
       <https://www.gnu.org/licenses/gpl-3.0.html> <?><?><?><?><?><?> 3
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       <<debian-l10n-russian@lists.debian.org>>.

<?><?><?><?><?><?><?><?><?><?> <?><?><?><?><?><?><?><?> Linux 6.9.1
                           15 <?><?><?><?> 2024 <?>.            makecontext(3)