97 lines
2.7 KiB
Groff
97 lines
2.7 KiB
Groff
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.TH GETCONTEXT 3 "Mar 2, 2010"
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.SH NAME
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getcontext, setcontext \- get and set current user context
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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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int getcontext(ucontext\_t *\fIucp\fP)
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int setcontext(const ucontext\_t *\fIoucp\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 \fIucontext_t\fP type is a structure that has at least the following members:
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.in +4
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.nf
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typedef struct __ucontext {
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ucontext_t *uc_link;
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sigset_t uc_sigmask;
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stack_t uc_stack;
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mcontext_t uc_mcontext;
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...
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} ucontext_t;
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.fi
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.in
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with \fIsigset_t\fP and \fIstack_t\fP defined in
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.IR <signal.h> .
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Here \fIuc_link\fP points to the context that will be resumed when the current context returns (if \fIuc_link\fP is NULL, the process exits), \fIsigset_t\fP is the set of signals blocks in this context, \fIuc_stack\fP is the stack used by this context (when the context was modified by
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.BR makecontext (3)),
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and \fIuc_mcontext\fP is the machine-specific representation of the saved context. The \fImcontext_t\fP type is machine-dependent and opaque.
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.PP
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MINIX 3 has an additional \fIuc_flags\fP member that supports the following flags:
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.PP
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.in +2
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.nf
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UCF_IGNSIGM /* Current signal mask is not stored or restored */
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UCF_IGNFPU /* FPU state is not stored or restored for this context */
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.fi
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.in
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.PP
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Not storing and restoring the signal mask and/or FPU state speeds up context switching considerably.
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.PP
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The
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.BR getcontext ()
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function initializes the structure pointed to by \fIucp\fP to the current user context of the calling thread.
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.PP
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The
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.BR setcontext ()
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function restores the user context pointed to by \fIucp\fP. A succesful call does not return; program execution resumes at the point specified by the \fIucp\fP argument passed to
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.BR setcontext ().
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The \fIucp\fP argument should be created either by a prior call to
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.BR getcontext ()
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or
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.BR makecontext ().
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If the \fIucp\fP argument was created with
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.BR getcontext (),
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program execution continues as if the corresponding call of
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.BR getcontext ()
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had just returned. If the \fIucp\fP argument was created with
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.BR makecontext (),
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program execution continues with the function passed to
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.BR makecontext ().
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.SH "RETURN VALUE"
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When successful,
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.BR getcontext ()
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returns 0 and
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.BR setcontext ()
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does not return. Otherwise, both return -1 and
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.I errno
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is set to indicate the error.
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.SH "ERRORS"
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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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[EFAULT]
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\fIucp\fP is a NULL pointer.
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.SH "SEE ALSO"
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.BR makecontext (3).
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.SH "AUTHORS"
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Thomas Veerman
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