getcontext(2)                    UNIX System V                    getcontext(2)


NAME
      getcontext, setcontext - get and set current user context

SYNOPSIS
      #include <ucontext.h>
      int getcontext(ucontextt *ucp);
      int setcontext(ucontextt *ucp);

DESCRIPTION
      These functions, along with those defined in makecontext(3C), are useful
      for implementing user level context switching between multiple threads of
      control within a process.

      getcontext initializes the structure pointed to by ucp to the current
      user context of the calling process.  The user context is defined by
      ucontext(5) and includes the contents of the calling process's machine
      registers, signal mask and execution stack.

      setcontext restores the user context pointed to by ucp.  The call to
      setcontext does not return;  program execution resumes at the point
      specified by the context structure passed to setcontext.  The context
      structure should have been one created either by a prior call to
      getcontext or makecontext or passed as the third argument to a signal
      handler [see sigaction(2)].  If the context structure was one created
      with getcontext, program execution continues as if the corresponding call
      of getcontext had just returned.  If the context structure was one
      created with makecontext, program execution continues with the function
      specified to makecontext.

NOTES
      When a signal handler is executed, the current user context is saved and
      a new context is created by the kernel.  If the process leaves the signal
      handler via longjmp(3C) the original context will not be restored, and
      future calls to getcontext will not be reliable.  Signal handlers should
      use siglongjmp(3C) or setcontext instead.

DIAGNOSTICS
      On successful completion, setcontext does not return and getcontext
      returns 0.  Otherwise, a value of -1 is returned and errno is set to
      indicate the error.

SEE ALSO
      sigaction(2), sigaltstack(2), sigprocmask(2), makecontext(3C),
      ucontext(5).










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