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getcontext(2)
NAME
  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
  ucp Provides a pointer to a ucontext structure, defined in the <ucontext.h>
      header file.  The ucontext structure contains the signal mask,
      execution 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 successful,
  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)

Index for Section 2

Alphabetical listing for G

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