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diff --git a/unix/os/doc/zsvjmp.hlp b/unix/os/doc/zsvjmp.hlp new file mode 100644 index 00000000..50e229f7 --- /dev/null +++ b/unix/os/doc/zsvjmp.hlp @@ -0,0 +1,65 @@ +.help zsvjmp,zdojmp May84 "System Interface" +.ih +NAME +zsvjmp, zdojmp -- non-local goto +.ih +SYNOPSIS +.nf +include <config.h> + +zsvjmp (jumpbuf, status) # save context for jump +zdojmp (jumpbuf, status) # restore context and jump + +int jumpbuf[LEN_JUMPBUF] # context saved by \fBzsvjmp\fR +int status # code returned by \fBzsvjmp\fR +.fi +.ih +DESCRIPTION +These primitives are used principally to restart interpreters (e.g. the IRAF +Main and the CL) following an error abort. +When an error occurs deep in a procedure calling sequence and the interpreter +(a higher level procedure) must be restarted, the hardware stack or stacks +and registers must be restored to their earlier state. + +The \fBzdojmp\fR primitive restores the context of the procedure which +originally called \fBzsvjmp\fR, causing control to return from \fBzsvjmp\fR +as if it had just been called. The calling procedure must not itself have +returned in the interim. +.ih +RETURN VALUE +The integer code \fIstatus\fR is zero the first time \fBzsvjmp\fR returns, +i.e., when \fBzsvjmp\fR is called by the main procedure to initialize +\fIjumpbuf\fR. When \fBzdojmp\fR is subsequently called to "goto" the +main procedure it should be called with a nonzero \fIstatus\fR to tell +the main procedure that it has been reentered at the point immediately +following the call to \fBzsvjmp\fR. +.ih +NOTES +Only the hardware stack and registers are restored by \fBzdojmp\fR. +Buffers which have been allocated since the first call to \fBzsvjmp\fR +will still be allocated, newly posted exception handlers will still be +posted, and so on. It is up to the high level code to clean up following +error restart. +.ih +EXAMPLE +Procedure A, the main (highest level) procedure, calls \fBzsvjmp\fR to +save its context for a subsequent restart, then calls procedure B. +Procedure B calls procedure C which directly or indirectly calls +\fBzdojmp\fR. The \fIjumpbuf\fR storage area is global. + +.ks +.nf +A: call zsvjmp (jumpbuf, status) + 99 if (status == error_code) + we were called from C + call B + +B: call C + +C: call zdojmp (jumpbuf, error_code) [e.g., goto 99] +.fi +.ke +.ih +SEE ALSO +A discussion of the IRAF Main and error recovery. +.endhelp |