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Name

makecontext, swapcontext - manipulate user contexts

Synopsis

#include <ucontext.h>

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

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

MT-Level

MT-Safe

Description

These functions are useful for implementing user-level context switching between multiple threads of control within a process.

makecontext() modifies the context specified by ucp, which has been initialized using getcontext(); when this context is resumed using swapcontext() or setcontext() (see getcontext(2) ), program execution continues by calling the function func, passing it the arguments that follow argc in the makecontext() call. The integer value of argc must be one-greater-than the number of arguments that follow argc; otherwise, the behavior is undefined. For 5 arguments, the value of argc must be 6.

swapcontext() saves the current context in the context structure pointed to by oucp and sets the context to the context structure pointed to by ucp.

Return Values

On successful completion, swapcontext return a value of zero. Otherwise, a value of -1 is returned and errno is set to indicate the error.

Errors

These functions will fail if either of the following is true:

EFAULT
ucp or oucp points to an invalid address.
ENOMEM
ucp does not have enough stack left to complete the operation.

See Also

exit(2) , getcontext(2) , sigaction(2) , sigprocmask(2) , ucontext(5)

Notes

The size of the ucontext_t structure may change in future releases. To remain binary compatible, users of these features must always use makecontext() or getcontext() to create new instances of them.

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