getcontext(3) [freebsd man page]
GETCONTEXT(3) BSD Library Functions Manual GETCONTEXT(3) NAME
getcontext, getcontextx, setcontext -- get and set user thread context LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <ucontext.h> int getcontext(ucontext_t *ucp); ucontext_t * getcontextx(void); int setcontext(const ucontext_t *ucp); DESCRIPTION
The getcontext() function saves the current thread's execution context in the structure pointed to by ucp. This saved context may then later be restored by calling setcontext(). The getcontextx() function saves the current execution context in the newly allocated structure ucontext_t, which is returned on success. If architecture defines additional CPU states that can be stored in extended blocks referenced from the ucontext_t, the memory for them may be allocated and their context also stored. Memory returned by getcontextx() function shall be freed using free(3). The setcontext() function makes a previously saved thread context the current thread context, i.e., the current context is lost and setcontext() does not return. Instead, execution continues in the context specified by ucp, which must have been previously initialized by a call to getcontext(), makecontext(3), or by being passed as an argument to a signal handler (see sigaction(2)). If ucp was initialized by getcontext(), then execution continues as if the original getcontext() call had just returned (again). If ucp was initialized by makecontext(3), execution continues with the invocation of the function specified to makecontext(3). When that function returns, ucp->uc_link determines what happens next: if ucp->uc_link is NULL, the process exits; otherwise, setcontext(ucp->uc_link) is implicitly invoked. If ucp was initialized by the invocation of a signal handler, execution continues at the point the thread was interrupted by the signal. RETURN VALUES
If successful, getcontext() returns zero and setcontext() does not return; otherwise -1 is returned. The getcontextx() returns pointer to the allocated and initialized context on success, and NULL on failure. ERRORS
No errors are defined for getcontext() or setcontext(). The getcontextx() may return the following errors in errno: [ENOMEM] No memory was available to allocate for the context or some extended state. SEE ALSO
sigaction(2), sigaltstack(2), makecontext(3), ucontext(3) BSD
March 13, 2013 BSD
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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)