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getcontext(2) [netbsd man page]

GETCONTEXT(2)						      BSD System Calls Manual						     GETCONTEXT(2)

getcontext, setcontext -- get and set current user context LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <ucontext.h> int getcontext(ucontext_t *ucp); int setcontext(const ucontext_t *ucp); DESCRIPTION
The getcontext() function initializes the object pointed to by ucp to the current user context of the calling thread. The user context defines a thread's execution environment and includes the contents of its machine registers, its signal mask, and its current execution stack. The setcontext() function restores the user context defined in the object pointed to by ucp as most recently initialized by a previous call to either getcontext() or makecontext(3). If successful, execution of the program resumes as defined in the ucp argument, and setcontext() will not return. If ucp was initialized by the getcontext() function, program execution continues as if the corresponding invocation of getcontext() had just returned (successfully). If ucp was initialized by the makecontext(3) function, program execution continues with the function (and function arguments) passed to makecontext(3). RETURN VALUES
On successful completion, getcontext() returns 0 and setcontext() does not return. Otherwise a value of -1 is returned and errno is set to indicate the error. ERRORS
The getcontext() and setcontext() functions will fail if: [EFAULT] The ucp argument points to an invalid address. The setcontext() function will fail if: [EINVAL] The contents of the datum pointed to by ucp are invalid. SEE ALSO
sigprocmask(2), longjmp(3), makecontext(3), setjmp(3), swapcontext(3) STANDARDS
The getcontext() and setcontext() functions conform to X/Open System Interfaces and Headers Issue 5 (``XSH5'') and IEEE Std 1003.1-2001 (``POSIX.1''). The errno indications are an extension to the standard. The IEEE Std 1003.1-2004 (``POSIX.1'') revision marked the functions getcontext() and setcontext() as obsolete, citing portability issues and recommending the use of POSIX threads instead. The IEEE Std 1003.1-2008 (``POSIX.1'') revision removed the functions from the specification. HISTORY
The getcontext() and setcontext() functions first appeared in AT&T System V Release 4 UNIX. BSD
April 28, 2010 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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