getcontext(2)                                                    getcontext(2)


NAME
     getcontext, setcontext - get and set current user context

SYNOPSIS
     #include <ucontext.h>
     int getcontext(ucontext_t *ucp);

     int setcontext(ucontext_t *ucp);

DESCRIPTION
     These functions, along with those defined in makecontext(3C), are useful
     for implementing user level context switching between multiple threads of
     control within a process.

     getcontext initializes the structure pointed to by ucp to the current
     user context of the calling process.  The user context is defined by
     ucontext(5) and includes the contents of the calling process's machine
     registers, signal mask and execution stack.

     setcontext restores the user context pointed to by ucp.  The call to
     setcontext does not return;  program execution resumes at the point
     specified by the context structure passed to setcontext.  The context
     structure should have been one created either by a prior call to
     getcontext or makecontext or passed as the third argument to a signal
     handler [see sigaction(2)].  If the context structure was one created
     with getcontext, program execution continues as if the corresponding call
     of getcontext had just returned.  If the context structure was one
     created with makecontext, program execution continues with the function
     specified to makecontext.

NOTES
     When a signal handler is executed, the current user context is saved and
     a new context is created by the kernel.  If the process leaves the signal
     handler via longjmp(3C) the original context will not be restored, and
     future calls to getcontext will not be reliable.  Signal handlers should
     use siglongjmp(3C) or setcontext instead.

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

SEE ALSO
     sigaction(2), sigaltstack(2), sigprocmask(2), makecontext(3C),
     ucontext(5).


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