Manual browser: setcontext(2)

GETCONTEXT(2) System Calls Manual GETCONTEXT(2)


getcontext, setcontextget and set current user context


Standard C Library (libc, -lc)


#include <ucontext.h>

getcontext(ucontext_t *ucp);

setcontext(const ucontext_t *ucp);


The getcontext() function initializes the object pointed to by ucp to the current user context of the calling thread. The user context defines a thread's execution environment and includes the contents of its machine registers, its signal mask, and its current execution stack.

The setcontext() function restores the user context defined in the object pointed to by ucp as most recently initialized by a previous call to either getcontext() or makecontext(3). If successful, execution of the program resumes as defined in the ucp argument, and setcontext() will not return. If ucp was initialized by the getcontext() function, program execution continues as if the corresponding invocation of getcontext() had just returned (successfully). If ucp was initialized by the makecontext(3) function, program execution continues with the function (and function arguments) passed to makecontext(3).


On successful completion, getcontext() returns 0 and setcontext() does not return. Otherwise a value of -1 is returned and errno is set to indicate the error.


The getcontext() and setcontext() functions will fail if:
The ucp argument points to an invalid address.

The setcontext() function will fail if:

The contents of the datum pointed to by ucp are invalid.


The getcontext() and setcontext() functions conform to X/Open System Interfaces and Headers Issue 5 (“XSH5”) and IEEE Std 1003.1-2001 (“POSIX.1”). The errno indications are an extension to the standard.

The IEEE Std 1003.1-2004 (“POSIX.1”) revision marked the functions getcontext() and setcontext() 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 specification.


The getcontext() and setcontext() functions first appeared in AT&T System V Release 4 UNIX.
April 28, 2010 NetBSD 7.0