Merge branch 'sv/format_status_error_info' into dev

* sv/format_status_error_info:
  Add support for the format_status callback to gen_event
  Extend format_status for gen_server/gen_fsm termination error logging

OTP-8630 sv/format_status_error_info

When a gen_server, gen_fsm process, or gen_event terminates abnormally,
sometimes the text representation of the process state can occupy many
lines of the error log, depending on the definition of the state term. A
mechanism to trim out parts of the state from the log has been added (using
a format_status/2 callback). See the documentation.

1 files changed, 44 insertions, 20 deletions

diff --git a/lib/stdlib/doc/src/gen_fsm.xml b/lib/stdlib/doc/src/gen_fsm.xml
index 739cd0bffd..d15383c621 100644
--- a/lib/stdlib/doc/src/gen_fsm.xml
+++ b/lib/stdlib/doc/src/gen_fsm.xml
@@ -4,7 +4,7 @@
 <erlref>
   <header>
     <copyright>
-      <year>1996</year><year>2009</year>
+      <year>1996</year><year>2010</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -13,12 +13,12 @@
       compliance with the License. You should have received a copy of the
       Erlang Public License along with this software. If not, it can be
       retrieved online at http://www.erlang.org/.
-    
+
       Software distributed under the License is distributed on an "AS IS"
       basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
       the License for the specific language governing rights and limitations
       under the License.
-    
+
     </legalnotice>
 
     <title>gen_fsm</title>
@@ -730,33 +730,58 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
       </desc>
     </func>
     <func>
-      <name>Module:format_status(normal, [PDict, StateData]) -> Status</name>
+      <name>Module:format_status(Opt, [PDict, StateData]) -> Status</name>
       <fsummary>Optional function for providing a term describing the
         current gen_fsm status.</fsummary>
       <type>
+        <v>Opt = normal | terminate</v>
         <v>PDict = [{Key, Value}]</v>
         <v>StateData = term()</v>
-        <v>Status = [term()]</v>
+        <v>Status = term()</v>
       </type>
       <desc>
-        <p><em>This callback is optional, so callback modules need not
-          export it. The gen_fsm module provides a default
-          implementation of this function that returns the callback
-          module state data.</em></p>
-        <p>This function is called by a gen_fsm process when one
-          of <seealso marker="sys#get_status/1">sys:get_status/1,2</seealso>
-          is invoked to get the gen_fsm status. A callback module
-          wishing to customise the <c>sys:get_status/1,2</c> return
-          value exports an instance of <c>format_status/2</c> that
-          returns a term describing the current status of the
-          gen_fsm.</p>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The gen_fsm module provides a default
+            implementation of this function that returns the callback
+            module state data.</p>
+        </note>
+        <p>This function is called by a gen_fsm process when:</p>
+        <list typed="bulleted">
+          <item>One
+            of <seealso marker="sys#get_status/1">sys:get_status/1,2</seealso>
+            is invoked to get the gen_fsm status. <c>Opt</c> is set to
+            the atom <c>normal</c> for this case.</item>
+          <item>The gen_fsm terminates abnormally and logs an
+            error. <c>Opt</c> is set to the atom <c>terminate</c> for
+            this case.</item>
+        </list>
+        <p>This function is useful for customising the form and
+          appearance of the gen_fsm status for these cases. A callback
+          module wishing to customise the <c>sys:get_status/1,2</c>
+          return value as well as how its status appears in
+          termination error logs exports an instance
+          of <c>format_status/2</c> that returns a term describing the
+          current status of the gen_fsm.</p>
         <p><c>PDict</c> is the current value of the gen_fsm's
           process dictionary.</p>
         <p><c>StateData</c> is the internal state data of the
           gen_fsm.</p>
-        <p>The function should return <c>Status</c>, a list of one or
-          more terms that customise the details of the current state
-          and status of the gen_fsm.</p>
+        <p>The function should return <c>Status</c>, a term that
+          customises the details of the current state and status of
+          the gen_fsm. There are no restrictions on the
+          form <c>Status</c> can take, but for
+          the <c>sys:get_status/1,2</c> case (when <c>Opt</c>
+          is <c>normal</c>), the recommended form for
+          the <c>Status</c> value is <c>[{data, [{"StateData",
+          Term}]}]</c> where <c>Term</c> provides relevant details of
+          the gen_fsm state data. Following this recommendation isn't
+          required, but doing so will make the callback module status
+          consistent with the rest of the <c>sys:get_status/1,2</c>
+          return value.</p>
+        <p>One use for this function is to return compact alternative
+          state data representations to avoid having large state terms
+          printed in logfiles.</p>
       </desc>
     </func>
   </funcs>
@@ -770,4 +795,3 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
       <seealso marker="sys">sys(3)</seealso></p>
   </section>
 </erlref>
-