70 lines
2.2 KiB
Groff
70 lines
2.2 KiB
Groff
.TH SETJMP 3 "June 22, 2006"
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.UC 4
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.SH NAME
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setjmp, longjmp, _setjmp, _longjmp, sigsetjmp, siglongjmp \- save and restore execution contexts
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.SH SYNOPSIS
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.nf
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.ft B
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#include <setjmp.h>
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int setjmp(jmp_buf env);
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void longjmp(jmp_buf env, int val);
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int _setjmp(jmp_buf env);
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void _longjmp(jmp_buf env, int val);
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#define _POSIX_SOURCE
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int sigsetjmp(sigjmp_buf env, int savemask);
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void siglongjmp(sigjmp_buf env, int val);
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.SH DESCRIPTION
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These calls provide a way for a process to save an execution context into a
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buffer, and later resume execution from that context, effectively performing
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a non-local jump. The
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.B setjmp
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family of functions store the context into the \fIenv\fP data structure,
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and return the value 0. The
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.B longjmp
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family of functions jump to the context saved in the given \fIenv\fP data
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structure, causing the process to continue as if it returned from the
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corresponding
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.B setjmp
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call again, but this time with the non-zero return value in \fIval\fP.
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.PP
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The difference between the three pairs of setjmp/longjmp functions lies in the
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behaviour with respect to saving/restoring the process signal mask. POSIX does
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not require the process signal mask to be saved and restored during
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.B setjmp
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/
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.B longjmp
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\. However, the current implementation does this in order to agree with OSF/1
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and other BSD derived systems.
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.PP
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The pair of functions
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.B _setjmp
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/
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.B _longjmp
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, traditional in BSD systems, may be used when the signal mask is not to be
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saved/restored.
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.PP
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Finally, the POSIX
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.B sigsetjmp
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/
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.B siglongjmp
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functions allow the programmer to specify explicitly whether the signal mask
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is to be saved/restored, by means of the \fIsavemask\fP parameter. If this
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parameter is zero, the signal mask will not be saved/restored, otherwise it
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will.
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.SH NOTES
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After the function calling
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.B setjmp
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has returned, the saved context may not be used in a call to
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.B longjmp
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anymore, since the relevant portion of the stack may already have been wiped
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out at that point.
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.PP
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Using these functions to return to a previous state from a signal handler
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is possible but should be done with extreme care, as some interrupted library
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routines may not be reentrant and/or temporarily allocate resources.
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.PP
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See the setjmp.h header file for more implementation details specific to Minix.
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