1.0.25.18: it's only SHOW

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

diff --git a/doc/internals/signals.texinfo b/doc/internals/signals.texinfo
index 1f27d3f..dc2b3a6 100644 (file)
--- a/doc/internals/signals.texinfo
+++ b/doc/internals/signals.texinfo
@@ -165,3 +165,17 @@ For the reasons above, calling user code, i.e. functions passed in, or
 in other words code that one cannot reason about, from non-reentrant
 code (holding locks), @code{WITHOUT-INTERRUPTS}, @code{WITHOUT-GCING}
 is dangerous and best avoided.
+
+@section Debugging
+
+It is not easy to debug signal problems. The best bet probably is to
+enable @code{QSHOW} and @code{QSHOW_SIGNALS} in runtime.h and once
+SBCL runs into problems attach gdb. A simple @code{thread apply all
+ba} is already tremendously useful. Another possibility is to send a
+SIGABORT to SBCL to provoke landing in LDB, if it's compiled with it
+and it has not yet done so on its own.
+
+Note, that fprintf used by QSHOW is not reentrant and at least on x86
+linux it is known to cause deadlocks, so place SHOW and co carefully,
+ideally to places where blockable signals are blocked. Use
+@code{QSHOW_SAFE} if you like.