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$FreeBSD: releng/10.2/lib/libc/gen/getcontext.3 248250 2013-03-13 18:18:16Z pluknet $
.Dd March 13, 2013 .Dt GETCONTEXT 3 .Os .Sh NAME .Nm getcontext , getcontextx , setcontext .Nd get and set user thread context .Sh LIBRARY .Lb libc .Sh SYNOPSIS n ucontext.h .Ft int .Fn getcontext "ucontext_t *ucp" .Ft ucontext_t * .Fn getcontextx "void" .Ft int .Fn setcontext "const ucontext_t *ucp" .Sh DESCRIPTION The .Fn getcontext function saves the current thread's execution context in the structure pointed to by .Fa ucp . This saved context may then later be restored by calling .Fn setcontext .
p The .Fn getcontextx function saves the current execution context in the newly allocated structure .Vt ucontext_t , which is returned on success. If architecture defines additional CPU states that can be stored in extended blocks referenced from the .Vt ucontext_t , the memory for them may be allocated and their context also stored. Memory returned by .Fn getcontextx function shall be freed using .Fn free 3 .
p The .Fn setcontext function makes a previously saved thread context the current thread context, i.e., the current context is lost and .Fn setcontext does not return. Instead, execution continues in the context specified by .Fa ucp , which must have been previously initialized by a call to .Fn getcontext , .Xr makecontext 3 , or by being passed as an argument to a signal handler (see .Xr sigaction 2 ) .
p If .Fa ucp was initialized by .Fn getcontext , then execution continues as if the original .Fn getcontext call had just returned (again).
p If .Fa ucp was initialized by .Xr makecontext 3 , execution continues with the invocation of the function specified to .Xr makecontext 3 . When that function returns, .Fa "ucp->uc_link" determines what happens next: if .Fa "ucp->uc_link" is .Dv NULL , the process exits; otherwise, .Fn setcontext "ucp->uc_link" is implicitly invoked.
p If .Fa ucp was initialized by the invocation of a signal handler, execution continues at the point the thread was interrupted by the signal. .Sh RETURN VALUES If successful, .Fn getcontext returns zero and .Fn setcontext does not return; otherwise -1 is returned. The .Fn getcontextx returns pointer to the allocated and initialized context on success, and .Va NULL on failure. .Sh ERRORS No errors are defined for .Fn getcontext or .Fn setcontext . The .Fn getcontextx may return the following errors in .Va errno : l -tag -width Er t Bq Er ENOMEM No memory was available to allocate for the context or some extended state. .El .Sh SEE ALSO .Xr sigaction 2 , .Xr sigaltstack 2 , .Xr makecontext 3 , .Xr ucontext 3