*** UNIX MANUAL PAGE BROWSER ***

getcontext(2) System Calls Manual getcontext(2) NAME getcontext, setcontext - Provides user level context switching SYNOPSIS #include <ucontext.h> int getcontext( ucontext_t *ucp); int setcontext( const ucontext_t *ucp); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: getcontext(), setcontext(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Provides a pointer to a ucontext structure, defined in the <ucontext.h> header file. The ucontext structure contains the signal mask, execu- tion stack, and machine registers. (See ucontext(5) for more informa- tion about the format of the ucontext structure.) DESCRIPTION Using both the getcontext() and setcontext() functions enables you to initiate user level context control, switching between multiple threads of control within a single process. When you call getcontext(), it initializes the ucp parameter to the current user context of the calling process. Use the setcontext() function to restore the state of the user context pointed to by the ucp parameter. The setcontext() function, if suc- cessful, does not return; application execution continues from the point specified by the ucontext structure you pass to the setcontext() function. The ucontext structure that you pass to the setcontext() function must either have been created by a call to the getcontext( function, or have been passed as the third parameter to a signal handler. (The third pa- rameter in a call to the sigaction() function determines the action to be performed when a signal is delivered. For more information, see sigaction(2).) When a context structure is created by the getcontext( function, execu- tion of the program continues as if the corresponding call of the get- context() function had just returned. RETURN VALUES The setcontext function does not return upon success. The getcontext function returns 0 (zero) upon success. Upon failure, both the setcon- text() and getcontext() functions return a value of -1. NOTES When a signal handler executes, the current user context is saved and a new context is created by the kernel. If the process leaves the signal handler using the longjmp() function, the original context cannot be restored, and the result of future calls to the getcontext() function are unpredictable. Use the siglongjmp() or setcontext() functions in signal handlers, instead of the longjmp() function. RELATED INFORMATION Functions: bsd_signal(2), makecontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), setjmp(3), sigsetjmp(3) Files: ucontext(5) Standards: standards(5) delim off getcontext(2)