From: Gabor M. <me...@us...> - 2009-02-16 22:20:44
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Update of /cvsroot/sbcl/sbcl/doc/internals In directory fdv4jf1.ch3.sourceforge.com:/tmp/cvs-serv10356/doc/internals Modified Files: signals.texinfo Log Message: 1.0.25.48: signals internals doc Index: signals.texinfo =================================================================== RCS file: /cvsroot/sbcl/sbcl/doc/internals/signals.texinfo,v retrieving revision 1.6 retrieving revision 1.7 diff -u -d -r1.6 -r1.7 --- signals.texinfo 16 Feb 2009 22:19:27 -0000 1.6 +++ signals.texinfo 16 Feb 2009 22:20:39 -0000 1.7 @@ -14,17 +14,16 @@ There are two distinct groups of signals. -@subsection Semi-synchronous signals +@subsection Synchronous signals -The first group, tentatively named ``semi-synchronous'', consists of -signals that are raised on illegal instruction, hitting a protected -page, or on a trap. Examples from this group are: +This group consists of signals that are raised on illegal instruction, +hitting a protected page, or on a trap. Examples from this group are: @code{SIGBUS}/@code{SIGSEGV}, @code{SIGTRAP}, @code{SIGILL} and @code{SIGEMT}. The exact meaning and function of these signals varies by platform and OS. Understandably, because these signals are raised in a controllable manner they are never blocked or deferred. -@subsection Blockable signals +@subsection Asynchronous or blockable signals The other group is of blockable signals. Typically, signal handlers block them to protect against being interrupted at all. For example @@ -70,6 +69,22 @@ deferrable by @code{WITHOUT-INTERRUPTS} is @code{SIG_STOP_FOR_GC}. It is deferred by pseudo atomic and @code{WITHOUT-GCING}. +@subsection When are signals handled? + +At once or as soon as the mechanism that deferred them allows. + +First, if something is deferred by pseudo atomic then it is run at the +end of pseudo atomic without exceptions. Even when both a GC request +or a @code{SIG_STOP_FOR_GC} and a deferrable signal such as +SIG_INTERRUPT_THREAD interrupts the pseudo atomic section. + +Second, an interrupt deferred by WITHOUT-INTERRUPTS is run when the +interrupts are enabled again. GC cannot interfere. + +Third, if GC or @code{SIG_STOP_FOR_GC} is deferred by +@code{WITHOUT-GCING} then the GC or stopping for GC will happen when +GC is not inhibited anymore. Interrupts cannot delay a gc. + @node Implementation warts @section Implementation warts @@ -93,9 +108,9 @@ the middle of an interrupted POSIX call. For some signals this appears to be a non-issue: @code{SIGSEGV} and -other semi-synchronous signals are raised by our code for our code, -and so we can be sure that we are not interrupting a POSIX call with -any of them. +other synchronous signals are raised by our code for our code, and so +we can be sure that we are not interrupting a POSIX call with any of +them. For asynchronous signals like @code{SIGALARM} and @code{SIGINT} this is a real issue. |