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Man Pages


Manual Reference Pages  -  SETCONTEXT (3)

NAME

getcontext, getcontextx, setcontext - get and set user thread context

CONTENTS

Library
Synopsis
Description
Return Values
Errors
See Also

LIBRARY


.Lb libc

SYNOPSIS


.In 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
.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 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)
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