better SIGNAL

[sbcl.git] / doc / internals / signals.texinfo

diff --git a/doc/internals/signals.texinfo b/doc/internals/signals.texinfo
index e5cfceb..e4aa90b 100644 (file)
--- a/doc/internals/signals.texinfo
+++ b/doc/internals/signals.texinfo
@@ -14,17 +14,16 @@
 
 There are two distinct groups of signals.
 
 
 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.
 
 @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
 
 The other group is of blockable signals. Typically, signal handlers
 block them to protect against being interrupted at all. For example

@@ -70,13 +69,29 @@ Something of a special case, a signal that is blockable but not
 deferrable by @code{WITHOUT-INTERRUPTS} is @code{SIG_STOP_FOR_GC}. It
 is deferred by pseudo atomic and @code{WITHOUT-GCING}.
 
 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
 
 @subsection Miscellaneous issues
 
 @node Implementation warts
 @section Implementation warts
 
 @subsection Miscellaneous issues
 

-Signal handlers should automatically restore errno and fp
-state. Currently, this is not the case.
+Signal handlers automatically restore errno and fp state, but
+arrange_return_to_lisp_function does not restore errno.

 
 @subsection POSIX -- Letter and Spirit
 
 
 @subsection POSIX -- Letter and Spirit
 

@@ -93,9 +108,9 @@ though we would no longer be in a signal handler, we might still be in
 the middle of an interrupted POSIX call.
 
 For some signals this appears to be a non-issue: @code{SIGSEGV} and
 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.
 
 For asynchronous signals like @code{SIGALARM} and @code{SIGINT} this
 is a real issue.