GETCONTEXT(2) Linux Programmer's Manual GETCONTEXT(2)NAME
getcontext, setcontext - get or set the user context
SYNOPSIS
#include <ucontext.h>
int getcontext(ucontext_t *ucp);
int setcontext(const ucontext_t *ucp);
where:
ucp points to a structure defined in <ucontext.h> containing the signal mask, execution stack, and machine registers.
DESCRIPTION getcontext(2) gets the current context of the calling process, storing it in the ucontext struct pointed to by ucp.
setcontext(2) sets the context of the calling process to the state stored in the ucontext struct pointed to by ucp. The struct must either
have been created by getcontext(2) or have been passed as the third parameter of the sigaction(2) signal handler.
The ucontext struct created by getcontext(2) is defined in <ucontext.h> as follows:
typedef struct ucontext
{
unsigned long int uc_flags;
struct ucontext *uc_link;
stack_t uc_stack;
mcontext_t uc_mcontext;
__sigset_t uc_sigmask;
struct _fpstate __fpregs_mem;
} ucontext_t;
RETURN VALUES getcontext(2) returns 0 on success and -1 on failure. setcontext(2) does not return a value on success and returns -1 on failure.
STANDARDS
These functions comform to: XPG4-UNIX.
NOTES
When a signal handler executes, the current user context is saved and a new context is created by the kernel. If the calling process
leaves the signal handler using longjmp(2), the original context cannot be restored, and the result of future calls to getcontext(2) are
unpredictable. To avoid this problem, use siglongjmp(2) or setcontext(2) in signal handlers instead of longjmp(2).
SEE ALSO sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3), setjmp(3).
Red Hat Linux 6.1 20 September 1999 GETCONTEXT(2)
Check Out this Related Man Page
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)