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Manual Pages  — MAKECONTEXT


makecontext – modify and exchange user thread contexts



Standard C Library (libc, -lc)


#include <ucontext.h>

makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...);

swapcontext(ucontext_t *oucp, const ucontext_t *ucp);


The makecontext() function modifies the user thread context pointed to by ucp, which must have previously been initialized by a call to getcontext(3) and had a stack allocated for it. The context is modified so that it will continue execution by invoking func() with the arguments provided. The argc argument must be equal to the number of additional arguments of type int provided to makecontext() and also equal to the number of arguments of type int to func(); otherwise , the behavior is undefined.

The ucp->uc_link argument must be initialized before calling makecontext() and determines the action to take when func() returns: if equal to NULL, the process exits; otherwise, setcontext(ucp->uc_link) is implicitly invoked.

The swapcontext() function saves the current thread context in *oucp and makes *ucp the currently active context.


If successful, swapcontext() returns zero; otherwise -1 is returned and the global variable errno is set appropriately.


The swapcontext() function will fail if:
  There is not enough stack space in ucp to complete the operation.


setcontext(3), ucontext(3)

MAKECONTEXT (3) January 31, 2018

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