98 lines
2.2 KiB
Groff
98 lines
2.2 KiB
Groff
.Dd Mar 2, 2010
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.Dt MAKECONTEXT 3
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.Os
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.Sh NAME
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.Nm makecontext ,
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.Nm swapcontext
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.Nd manipulate user contexts
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In ucontext.h
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.Ft void
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.Fn makecontext "ucontext_t *ucp" "void (*func)(void)" "int argc" ...
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.Ft int
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.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp"
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.Sh DESCRIPTION
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The
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.Xr makecontext 3 ,
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.Xr swapcontext 3 ,
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.Xr getcontext 3 ,
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and
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.Xr setcontext 3
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together form a set of functions that allow user-level context switching between multiple threads of control within a process.
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.Pp
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The
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.Fn makecontext
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function modifies the user thread pointed to by
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.Va ucp
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to continue execution by invoking function
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.Va func
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and passing that function a number of
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.Va argc
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integer arguments. The value of
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.Va argc
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must match the number of integer arguments passed to
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.Va func ,
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otherwise the behavior is undefined. Context
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.Va ucp
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must have been initialized by a call to
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.Xr getcontext 3
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and have a stack allocated for it. The address of the stack must be assigned to
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.Va ucp->uc_stack.ss_sp
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and the size of the stack to
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.Va ucp->uc_stack.ss_size .
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The
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.Va ucp->uc_link
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member is used to determine which successor context is run after the context modified by
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.Fn makecontext
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returns. If left NULL, the process exits.
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.Pp
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The
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.Fn swapcontext
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function saves the current context in the context structure pointed to by
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.Va oucp
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and sets the context to the context structure pointed to by
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.Va ucp .
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.Sh RETURN VALUES
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When successful,
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.Fn swapcontext
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returns 0. Otherwise, -1 is returned and
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.Va errno
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is set to indicate the error. Note that a successful call to
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.Fn swapcontext
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actually does not return. Only after returning to the context that called
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.Fn swapcontext ,
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it appears as if
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.Fn swapcontext
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returned 0.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EFAULT
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Either the
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.Va ucp
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or
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.Va oucp
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is a NULL pointer.
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.It Bq Er EINVAL
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The context is not properly initialized.
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.It Bq Er ENOMEM
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The
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.Va ucp
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argument does not have enough stack left to complete the operation.
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.El
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.Sh SEE ALSO
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.Xr getcontext 3 ,
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.Xr setcontext 3
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.Sh STANDARDS
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The
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.Fn makecontext ,
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and
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.Fn swapcontext
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functions conform to
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.St -xsh5
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and
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.St -p1003.1-2001 .
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.Sh AUTHORS
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Thomas Veerman
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