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getcontext(3) [freebsd man page]

GETCONTEXT(3)						   BSD Library Functions Manual 					     GETCONTEXT(3)

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 Manual						     getcontext(2)

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)
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