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At Erlang Factory 2013 there was discussion during one of the talks about
the sys:get_status functions and how useful they were for debugging. Geoff
Cant mentioned it would be very useful if the sys module also provided
functions to use while debugging to get just the state of a process and
also to be able to replace the state of a process, and many others in the
audience appeared to agree.
The sys:get_state/1,2 functions return the state of a gen_server, gen_fsm,
or gen_event process. The return value varies depending on the process
type: process state for a gen_server, state name and state data for a
gen_fsm, and handler module, handler id, and handler state for each handler
registered in a gen_event process.
The sys:replace_state/2,3 functions allow the state of a gen_server,
gen_fsm, or gen_event process to be replaced with a new state. These
functions take a function argument that updates or replaces the process
state; using a function to change the state eliminates the race condition
of first reading the state via sys:get_state/1 or sys:get_state/2, using
its return value to create a new state, and then replacing the old state
with the new state, since during that time the process might have received
other calls or messages that could have changed its state.
* For a gen_server process, the state replacement function takes the
process state as an argument and returns a new state.
* For a gen_fsm process, the state replacement function gets a tuple of
{StateName, StateData} and returns a similar tuple that specifies a new
state name, new state data, or both.
* For a gen_event process, the state replacement function is called for
each registered event handler. It gets a tuple {Module, Id, HandlerState}
and returns a similar tuple that specifies the same Module and Id values
but may specify a different value for HandlerState.
If the state replacement function crashes or results in an error, the
original state of a gen_server or gen_fsm process is maintained; if such a
crash occurs for a gen_event process, the original state of the event
handler for which the state replacement function was called is maintained,
but the states of other event handlers of the same gen_event process may
still be updated if no errors or crashes occur while replacing their
states.
Add documentation for sys:get_state/1,2 and sys:replace_state/2,3. The
documentation explicitly notes that the functions are intended for use
during debugging.
Add new tests for these functions to gen_server_SUITE, gen_fsm_SUITE, and
gen_event_SUITE.
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* uw/extending_gen:
Add plugin support for alternative name lookup
OTP-9945
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OTP behaviour instances (gen_server, gen_fsm, gen_event) can currently
register themselves either locally or globally, and the behaviour
libraries (including gen.erl) support both addressing methods, as well
as the normal Pid and {Name, Node}.
However, there are alternative registry implementations - e.g. gproc -
and one can well imagine other ways of locating a behaviour instance,
e.g. on a node connected only via a TCP tunnel, rather than via
Distributed Erlang. In all these cases, one needs to write extra code
to identify the behaviour instance, even though the instance itself
need not be aware of how it is located.
This patch introduces a new way of locating a behaviour instance:
{via, Module, Name}.
Module is expected to export a subset of the functions in global.erl,
namely:
register_name(Name, Pid) -> yes | no
whereis_name(Name) -> pid() | undefined
unregister_name(Name) -> ok
send(Name, Msg) -> Pid
Semantics are expected to be the same as for global.erl
This can be used in all places where {global, Name} is accepted.
faulty export in gen_fsm_SUITE.erl
await process death in dummy_via:reset()
fix error in gen_[server|fsm]:enter_loop()
fix documentation
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Calls to global:whereis_name/1 have been substituted for calls to
global:safe_whereis_name/1 since the latter is not safe at all.
The reason for not doing this earlier is that setting a global lock
masked out a bug concerning the restart of supervised children. The
bug has now been fixed by a modification of global:whereis_name/1.
(Thanks to Ulf Wiger for code contribution.)
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Fixed a minor race conditions in gen_fsm:start*: if one of these
functions returned {error,Reason} or ignore, the name could still be
registered (either locally or in global.
This is the same modification as was done for gen_server in OTP-7669.
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Replace the behaviour_info(callbacks) export in stdlib's behaviours with
-callback' attributes for all the callbacks.
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This commit is a preparation for introducing location information
(filename/line number) in stacktraces in exceptions. Currently
a stack trace looks like:
[{Mod1,Function1,Arity1},
.
.
.
{ModN,FunctionN,ArityN}]
Add a forth element to each tuple that can be used indication
the filename and line number of the source file:
[{Mod1,Function1,Arity1,Location1},
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.
.
{ModN,FunctionN,ArityN,LocationN}]
In this commit, the fourth element will just be an empty list,
and we will change all code that look at or manipulate stacktraces.
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Port the gen_fsm code for format_status to gen_event in order to
prevent a lists:concat([...,pid()]) crash when calling
sys:get_status/1 on an unregistered gen_event process.
Refactor format_status header code from gen_* behaviours to module gen.
Extend the format_status tests in gen_event_SUITE to cover
format_status bugs with anonymous gen_event processes.
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The gen_fsm, gen_server, and wx_object format_status implementations
fail to handle global names of the form {global, term()} where term()
is something other than an atom, pid, or list. Change these
format_status implementations to treat names that are atoms, pids, or
lists as before, but for all other terms, set the header property of
the function return value to a tuple whose first element is a string
describing the return value and whose second element is the name term.
Add unit tests for gen_server and gen_fsm to verify sys:get_status
calls work successfully for globally registered instances.
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When a gen_server or gen_fsm process 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. Developers sometimes would like a way to trim out parts of the
state from the log if those parts don't contribute to documenting the
circumstances of the error, thereby helping to reduce the amount of
logged output.
Since the format_status callback can already format and specialize
gen_server and gen_fsm state for inclusion in the term returned from
sys:get_status, this patch extends format_status in a
backward-compatible way to also be able to specialize the state logged
for abnormal gen_server and gen_fsm termination, and includes new unit
tests to verify the new functionality.
This patch also eliminates the previous restriction that the status
returned by format_status must be a list. It can now be any term.
The documentation is extended to cover the new usage for
format_status, and it's been improved to recommend a form for the
normal case that allows the returned status to fit well with the rest
of the term returned by sys:get_status. The documentation is clear
that this form is only recommended, not required.
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* ks/stdlib:
erl_parse.yrl: Add missing operator in type declaration
stdlib: Add types and specs
stdlib: Use fun object instead of {M,F} tuple
ets: Cleanup as suggested by tidier
OTP-8576 ks/stdlib
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gen_fsm:format_status/2 currently crashes if Name in the process
state is a Pid.
Handle Name in the same way as in gen_server:format_status/2
to eliminate the crash.
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