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PACKET DESIGN DOES NOT WARRANT, GUARANTEE, 23.\" OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS 24.\" OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, 25.\" RELIABILITY OR OTHERWISE. IN NO EVENT SHALL PACKET DESIGN BE 26.\" LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE 27.\" OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT, 28.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL 29.\" DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF 30.\" USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF 31.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 32.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF 33.\" THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF 34.\" THE POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" $FreeBSD$ 37.\" 38.Dd March 23, 2020 39.Dt GETCONTEXT 3 40.Os 41.Sh NAME 42.Nm getcontext , getcontextx , setcontext 43.Nd get and set user thread context 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In ucontext.h 48.Ft int 49.Fn getcontext "ucontext_t *ucp" 50.Ft ucontext_t * 51.Fn getcontextx "void" 52.Ft int 53.Fn setcontext "const ucontext_t *ucp" 54.Sh DESCRIPTION 55The 56.Fn getcontext 57function 58saves the current thread's execution context in the structure pointed to by 59.Fa ucp . 60This saved context may then later be restored by calling 61.Fn setcontext . 62.Pp 63The 64.Fn getcontextx 65function saves the current execution context in the newly allocated structure 66.Vt ucontext_t , 67which is returned on success. 68If architecture defines additional CPU states that can be stored in extended 69blocks referenced from the 70.Vt ucontext_t , 71the memory for them may be allocated and their context also stored. 72Memory returned by 73.Fn getcontextx 74function shall be freed using 75.Fn free 3 . 76.Pp 77The 78.Fn setcontext 79function 80makes a previously saved thread context the current thread context, i.e., 81the current context is lost and 82.Fn setcontext 83does not return. 84Instead, execution continues in the context specified by 85.Fa ucp , 86which must have been previously initialized by a call to 87.Fn getcontext , 88.Xr makecontext 3 , 89or by being passed as an argument to a signal handler (see 90.Xr sigaction 2 ) . 91.Pp 92If 93.Fa ucp 94was initialized by 95.Fn getcontext , 96then execution continues as if the original 97.Fn getcontext 98call had just returned (again). 99.Pp 100If 101.Fa ucp 102was initialized by 103.Xr makecontext 3 , 104execution continues with the invocation of the function specified to 105.Xr makecontext 3 . 106When that function returns, 107.Fa "ucp->uc_link" 108determines what happens next: 109if 110.Fa "ucp->uc_link" 111is 112.Dv NULL , 113the process exits; 114otherwise, 115.Fn setcontext "ucp->uc_link" 116is implicitly invoked. 117.Pp 118If 119.Fa ucp 120was initialized by the invocation of a signal handler, execution continues 121at the point the thread was interrupted by the signal. 122.Sh RETURN VALUES 123If successful, 124.Fn getcontext 125returns zero and 126.Fn setcontext 127does not return; otherwise \-1 is returned. 128The 129.Fn getcontextx 130returns pointer to the allocated and initialized context on success, and 131.Va NULL 132on failure. 133.Sh ERRORS 134No errors are defined for 135.Fn getcontext 136or 137.Fn setcontext . 138The 139.Fn getcontextx 140may return the following errors in 141.Va errno : 142.Bl -tag -width Er 143.It Bq Er ENOMEM 144No memory was available to allocate for the context or some extended state. 145.El 146.Sh SEE ALSO 147.Xr sigaction 2 , 148.Xr sigaltstack 2 , 149.Xr makecontext 3 , 150.Xr ucontext 3 151.Sh STANDARDS 152The 153.Fn getcontext 154and 155.Fn setcontext 156functions conform to 157.St -xsh5 158and 159.St -p1003.1-2001 . 160The 161.Va errno 162indications are an extension to the standard. 163.Pp 164The 165.St -p1003.1-2004 166revision marked the functions 167.Fn getcontext 168and 169.Fn setcontext 170as obsolete, citing portability issues and recommending the use of 171.Tn POSIX 172threads instead. 173The 174.St -p1003.1-2008 175revision removed the functions from the specification. 176.Sh HISTORY 177The 178.Fn getcontext 179and 180.Fn setcontext 181functions first appeared in 182.At V.4 . 183