makecontext(3) [netbsd man page]
MAKECONTEXT(3) BSD Library Functions Manual MAKECONTEXT(3) NAME
makecontext, swapcontext -- manipulate user contexts LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <ucontext.h> void makecontext(ucontext_t *ucp, void (*func)(), int argc, ...); int swapcontext(ucontext_t * restrict oucp, ucontext_t * restrict ucp); DESCRIPTION
The makecontext() function modifies the object pointed to by ucp, which has been initialized using getcontext(2). When this context is resumed using swapcontext() or setcontext(2), program execution continues as if func had been called with the arguments specified after argc in the call of makecontext(). The value of argc must be equal to the number of integer arguments following it, and must be equal to the num- ber of integer arguments expected by func; otherwise, the behavior is undefined. Before being modified using makecontext(), a stack must be allocated for the context (in the uc_stack member), and a context to resume after func has returned must be determined (pointed to by the uc_link member); otherwise, the behavior is undefined. If uc_link is a null pointer, then the context is the main context, and the process will exit with an exit status of 0 upon return. The swapcontext() function saves the current context in the object pointed to by oucp, sets the current context to that specified in the object pointed to by ucp, and resumes execution. When a context saved by swapcontext() is restored using setcontext(2), execution will resume as if the corresponding invocation of swapcontext() had just returned (successfully). RETURN VALUES
The makecontext() function returns no value. On success, swapcontext() returns a value of 0, Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The swapcontext() function will fail if: [EFAULT] The oucp argument or the ucp argument points to an invalid address. [EINVAL] The contents of the datum pointed to by ucp are invalid. SEE ALSO
_exit(2), getcontext(2), setcontext(2), ucontext(2) STANDARDS
The makecontext() and swapcontext() functions conform to X/Open System Interfaces and Headers Issue 5 (``XSH5'') and IEEE Std 1003.1-2001 (``POSIX.1''). The IEEE Std 1003.1-2004 (``POSIX.1'') revision marked the functions makecontext() and swapcontext() as obsolete, citing portability issues and recommending the use of POSIX threads instead. The IEEE Std 1003.1-2008 (``POSIX.1'') revision removed the functions from the specifica- tion. The standard does not clearly define the type of integer arguments passed to func via makecontext(); portable applications should not rely on the implementation detail that it may be possible to pass pointer arguments to functions. This may be clarified in a future revision of the standard. HISTORY
The makecontext() and swapcontext() functions first appeared in AT&T System V Release 4 UNIX. BSD
May 4, 2012 BSD
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MAKECONTEXT(P) POSIX Programmer's Manual MAKECONTEXT(P) NAME
makecontext, swapcontext - manipulate user contexts SYNOPSIS
#include <ucontext.h> void makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...); int swapcontext(ucontext_t *restrict oucp, const ucontext_t *restrict ucp); DESCRIPTION
The makecontext() function shall modify the context specified by ucp, which has been initialized using getcontext(). When this context is resumed using swapcontext() or setcontext(), program execution shall continue by calling func, passing it the arguments that follow argc in the makecontext() call. Before a call is made to makecontext(), the application shall ensure that the context being modified has a stack allocated for it. The application shall ensure that the value of argc matches the number of arguments of type int passed to func; otherwise, the behavior is undefined. The uc_link member is used to determine the context that shall be resumed when the context being modified by makecontext() returns. The application shall ensure that the uc_link member is initialized prior to the call to makecontext(). The swapcontext() function shall save the current context in the context structure pointed to by oucp and shall set the context to the con- text structure pointed to by ucp. RETURN VALUE
Upon successful completion, swapcontext() shall return 0. Otherwise, -1 shall be returned and errno set to indicate the error. ERRORS
The swapcontext() function shall fail if: ENOMEM The ucp argument does not have enough stack left to complete the operation. The following sections are informative. EXAMPLES
The following example illustrates the use of makecontext(): #include <stdio.h> #include <ucontext.h> static ucontext_t ctx[3]; static void f1 (void) { puts("start f1"); swapcontext(&ctx[1], &ctx[2]); puts("finish f1"); } static void f2 (void) { puts("start f2"); swapcontext(&ctx[2], &ctx[1]); puts("finish f2"); } int main (void) { char st1[8192]; char st2[8192]; getcontext(&ctx[1]); ctx[1].uc_stack.ss_sp = st1; ctx[1].uc_stack.ss_size = sizeof st1; ctx[1].uc_link = &ctx[0]; makecontext(&ctx[1], f1, 0); getcontext(&ctx[2]); ctx[2].uc_stack.ss_sp = st2; ctx[2].uc_stack.ss_size = sizeof st2; ctx[2].uc_link = &ctx[1]; makecontext(&ctx[2], f2, 0); swapcontext(&ctx[0], &ctx[2]); return 0; } APPLICATION USAGE
None. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
exit() , getcontext() , sigaction() , sigprocmask() , the Base Definitions volume of IEEE Std 1003.1-2001, <ucontext.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 MAKECONTEXT(P)