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authorSteve Vinoski <[email protected]>2014-03-19 11:45:11 -0400
committerSteve Vinoski <[email protected]>2014-03-21 10:19:51 -0400
commit6c298a7bfa332e5b7d153648d741740abc3bcdf8 (patch)
tree3f8a5604555b8a3b959c5184bba59d9c65b0da3a /system/doc/design_principles
parent73af231f1a22083031df49ba19fdfd4f6b434a10 (diff)
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fix sys:get_state/1,2 and sys:replace_state/2,3 when sys suspended
Add two new system callbacks Module:system_get_state/1 and Module:system_replace_state/2 to allow sys:get_state/1,2 and sys:replace_state/2,3 to operate correctly even if a process is sys suspended. Modify gen_server, gen_fsm, and gen_event to support the new callbacks. If a callback module does not export these functions, then by default the Misc value (the same as that passed as the final argument to sys:handle_system_msg/6, and returned as part of the return value of sys:get_status/1,2) is treated as the callback module's state. The previous behaviour of intercepting the system message and passing a tuple of size 2 as the last argument to sys:handle_system_msg/6 is no longer supported. Add tests to verify the correctness of sys:get_state/1,2 and sys:replace_state/2,3 when processes are sys suspended. Add two tests for modules that implement special processes, one that exports system_get_state/1 and system_replace_state/2 and one that doesn't. Much of the credit for this patch goes to James Fish, who reported the initial problem and implemented much of the fix.
Diffstat (limited to 'system/doc/design_principles')
-rw-r--r--system/doc/design_principles/spec_proc.xml40
1 files changed, 36 insertions, 4 deletions
diff --git a/system/doc/design_principles/spec_proc.xml b/system/doc/design_principles/spec_proc.xml
index 8de7a5fe03..d55427aa10 100644
--- a/system/doc/design_principles/spec_proc.xml
+++ b/system/doc/design_principles/spec_proc.xml
@@ -130,7 +130,8 @@ ok
-export([alloc/0, free/1]).
-export([init/1]).
-export([system_continue/3, system_terminate/4,
- write_debug/3]).
+ write_debug/3,
+ system_get_state/1, system_replace_state/2]).
start_link() ->
proc_lib:start_link(ch4, init, [self()]).
@@ -177,9 +178,21 @@ loop(Chs, Parent, Deb) ->
system_continue(Parent, Deb, Chs) ->
loop(Chs, Parent, Deb).
-system_terminate(Reason, Parent, Deb, Chs) ->
+system_terminate(Reason, _Parent, _Deb, _Chs) ->
exit(Reason).
+system_get_state(Chs) ->
+ {ok, Chs}.
+
+system_replace_state(StateFun, Chs) ->
+ try
+ NChs = StateFun(Chs),
+ {ok, NChs, NChs}
+ catch
+ _:_ ->
+ {ok, Chs, Chs}
+ end.
+
write_debug(Dev, Event, Name) ->
io:format(Dev, "~p event = ~p~n", [Name, Event]).</pre>
<p>Example on how the simple debugging functions in <c>sys</c> can
@@ -366,8 +379,15 @@ Module:system_terminate(Reason, Parent, Deb, State)</code>
<item><c>Module</c> is the name of the module.</item>
<item><c>Deb</c> is the debug structure.</item>
<item><c>State</c> is a term describing the internal state and
- is passed to <c>system_continue</c>/<c>system_terminate</c>.</item>
+ is passed to <c>system_continue</c>/<c>system_terminate</c>/
+ <c>system_get_state</c>/<c>system_replace_state</c>.</item>
</list>
+ <p>If the process should return its state <c>handle_system_msg</c> will call:</p>
+ <code type="none">
+Module:system_get_state(State)</code>
+ <p>or if the process should replace its state using the fun <c>StateFun</c>:</p>
+ <code type="none">
+Module:system_replace_state(StateFun, State)</code>
<p>In the example:</p>
<code type="none">
loop(Chs, Parent, Deb) ->
@@ -383,7 +403,19 @@ system_continue(Parent, Deb, Chs) ->
loop(Chs, Parent, Deb).
system_terminate(Reason, Parent, Deb, Chs) ->
- exit(Reason).</code>
+ exit(Reason).
+
+system_get_state(Chs) ->
+ {ok, Chs, Chs}.
+
+system_replace_state(StateFun, Chs) ->
+ try
+ NChs = StateFun(Chs),
+ {ok, NChs, NChs}
+ catch
+ _:_ ->
+ {ok, Chs, Chs}
+ end.</code>
<p>If the special process is set to trap exits, note that if
the parent process terminates, the expected behavior is to
terminate with the same reason:</p>