76 lines
2 KiB
Groff
76 lines
2 KiB
Groff
.TH MAKECONTEXT 3 "Mar 2, 2010"
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.SH NAME
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makecontext, swapcontext \- manipulate user contexts
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.SH SYNOPSIS
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.nf
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.ft B
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#include <ucontext.h>
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void makecontext(ucontext\_t *\fIucp\fP, void \fI(*func)(void)\fP, int \fIargc\fP, ...)
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int swapcontext(ucontext\_t *\fIoucp\fP, const ucontext\_t *\fIucp\fP)
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.SH DESCRIPTION
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The
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.BR makecontext (3)
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,
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.BR swapcontext (3)
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,
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.BR getcontext (3)
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, and
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.BR 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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.BR makecontext ()
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function modifies the user thread pointed to by
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.I ucp
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to continue execution by invoking function
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.I func
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and passing that function a number of
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.I argc
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integer arguments. The value of
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.I argc
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must match the number of integer arguments passed to
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.I func
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, otherwise the behavior is undefined. Context
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.I ucp
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must have been initialized by a call to
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.BR getcontext (3)
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and have a stack allocated for it. The address of the stack must be assigned to \fIucp\->uc_stack.ss_sp\fP and the size of the stack to \fIucp\->uc_stack.ss_size\fP. The \fIucp\->uc_link\fP member is used to determine which successor context is run after the context modified by
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.BR 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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.BR swapcontext ()
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function saves the current context in the context structure pointed to by
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.I oucp
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and sets the context to the context structure pointed to by \fIucp\fP.
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.SH "RETURN VALUE"
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When successful,
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.BR swapcontext ()
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returns 0. Otherwise, -1 is returned and
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.I errno
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is set to indicate the error. Note that a successful call to
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.BR swapcontext ()
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actually does not return. Only after returning to the context that called
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.BR swapcontext ()
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, it appears as if
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.BR swapcontext ()
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returned 0.
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.SH "ERRORS"
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.TP 15
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[EFAULT]
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Either the \fIucp\fP or \fIoucp\fP is a NULL pointer.
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.TP 15
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[EINVAL]
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The context is not properly initialized.
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.TP 15
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[ENOMEM]
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The \fIucp\fP argument does not have enough stack left to complete the operation.
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.SH "SEE ALSO"
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.BR getcontext (3).
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.SH "AUTHORS"
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Thomas Veerman
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