setcontext(2) [sunos man page]
getcontext(2) System Calls getcontext(2) NAME
getcontext, setcontext - get and set current user context SYNOPSIS
#include <ucontext.h> int getcontext(ucontext_t *ucp); int setcontext(const ucontext_t *ucp); DESCRIPTION
The getcontext() function initializes the structure pointed to by ucp to the current user context of the calling process. The ucontext_t type that ucp points to defines the user context and includes the contents of the calling process' machine registers, the signal mask, and the current execution stack. The setcontext() function restores the user context pointed to by ucp. A successful call to setcontext() does not return; program execu- tion resumes at the point specified by the ucp argument passed to setcontext(). The ucp argument should be created either by a prior call to getcontext(), or by being passed as an argument to a signal handler. If the ucp argument was created with getcontext(), program execu- tion continues as if the corresponding call of getcontext() had just returned. If the ucp argument was created with makecontext(3C), pro- gram execution continues with the function passed to makecontext(3C). When that function returns, the process continues as if after a call to setcontext() with the ucp argument that was input to makecontext(3C). If the ucp argument was passed to a signal handler, program execu- tion continues with the program instruction following the instruction interrupted by the signal. If the uc_link member of the ucontext_t structure pointed to by the ucp argument is equal to 0, then this context is the main context, and the process will exit when this context returns. The effects of passing a ucp argument obtained from any other source are unspecified. RETURN VALUES
On successful completion, setcontext() does not return and getcontext() returns 0. Otherwise, -1 is returned. ERRORS
No errors are defined. USAGE
When a signal handler is executed, the current user context is saved and a new context is created. If the thread leaves the signal handler via longjmp(3UCB), then it is unspecified whether the context at the time of the corresponding setjmp(3UCB) call is restored and thus whether future calls to getcontext() will provide an accurate representation of the current context, since the context restored by longjmp(3UCB) may not contain all the information that setcontext() requires. Signal handlers should use siglongjmp(3C) instead. Portable applications should not modify or access the uc_mcontext member of ucontext_t. A portable application cannot assume that context includes any process-wide static data, possibly including errno. Users manipulating contexts should take care to handle these explicitly when required. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
sigaction(2), sigaltstack(2), sigprocmask(2), bsd_signal(3C), makecontext(3C), setjmp(3UCB), sigsetjmp(3C), ucontext.h(3HEAD), attributes(5), standards(5) SunOS 5.10 5 Feb 2001 getcontext(2)
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getcontext(2) System Calls Manual getcontext(2) NAME
getcontext, setcontext - Initiates and restores 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 standards as follows: getcontext(), setcontext(): XSH5.0 Refer to the standards(5) reference page for more information about industry 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, exe- cution stack, and machine registers. (See ucontext(5) for more information 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 argument 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 argument. 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 have been created by a call to the getcontext() function or the makecontext() function, or have been passed as the third argument to a signal handler. (The third argument 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, execution of the program continues as if the corresponding call of the getcontext() function had just returned. When a context structure is created by the makecontext() function, program execution continues with the function passed to makecontext(). When that function returns, the thread continues as if after a call to setcontext() with the context structure argument that was input to makecontext(). If the uc_link member of the ucontext_t structure pointed to by the ucp argument is 0 (zero), then this context is the main context, and the thread will exit when this context returns. The effects of passing a ucp argument from any other source are unspecified. 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. RETURN VALUES
The setcontext() function does not return upon success. The getcontext() function returns 0 (zero) upon success. Upon failure, both the setcontext() and getcontext() functions return a value of -1. SEE ALSO
Functions: bsd_signal(2), makecontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), setjmp(3), sigsetjmp(3) Files: ucontext(5) Standards: standards(5) getcontext(2)