nickva commented on a change in pull request #761: Add a debugging utilities
for listing processes
URL: https://github.com/apache/couchdb/pull/761#discussion_r134802001
##########
File path: src/couch/src/couch_debug.erl
##########
@@ -13,11 +13,195 @@
-module(couch_debug).
-export([
+ help/0,
+ help/1
+]).
+
+-export([
opened_files/0,
opened_files_by_regexp/1,
opened_files_contains/1
]).
+-export([
+ process_name/1,
+ link_tree/1,
+ link_tree/2,
+ mapfold_tree/3,
+ map_tree/2,
+ fold_tree/3,
+ linked_processes_info/2,
+ print_linked_processes/1
+]).
+
+help() ->
+ [
+ opened_files,
+ opened_files_by_regexp,
+ opened_files_contains,
+ process_name,
+ link_tree,
+ mapfold,
+ map,
+ fold,
+ linked_processes_info,
+ print_linked_processes,
+ ps
+ ].
+
+-spec help(Function :: atom()) -> ok.
+help(opened_files) ->
+ io:format("
+ opened_files()
+ --------------
+
+ Returns list of currently opened files
+ It iterates through erlang:ports and filter out all ports which are not
efile.
+ It uses `process_info(Pid, dictionary)` to get info about couch_file
properties.
+ ---
+ ", []);
+help(opened_files_by_regexp) ->
+ io:format("
+ opened_files_by_regexp(FileRegExp)
+ ----------------------------------
+
+ Returns list of currently opened files which name matches provided regular
expression.
+ It iterates through `erlang:ports()` and filter out all ports which are
not efile.
+ It uses `process_info(Pid, dictionary)` to get info about couch_file
properties.
+ ---
+ ", []);
+help(opened_files_contains) ->
+ io:format("
+ opened_files_contains(SubString)
+ --------------------------------
+
+ Returns list of currently opened files which name contains provided
SubString.
+ It iterates through `erlang:ports()` and filter out all ports which are
not efile.
+ It uses `process_info(Pid, dictionary)` to get info about couch_file
properties.
+ ---
+ ", []);
+help(process_name) ->
+ io:format("
+ process_name(Pid)
+ -----------------
+
+ Uses heuristics to figure out the best way to name process.
+ The heuristic is based on the following information about the process:
+ - process_info(Pid, registered_name)
+ - '$initial_call' key in process dictionary
+ - process_info(Pid, initial_call)
+
+ ---
+ ", []);
+help(link_tree) ->
+ io:format("
+ link_tree(Pid)
+ --------------
+
+ Returns a tree which represents a cluster of linked processes.
+ This function receives the initial Pid to start from.
+ The function doesn't recurse to pids older than initial one.
+ The Pids which are lesser than initial Pid are still shown in the output.
+ This is analogue of `link_tree(RootPid, []).`
+
+ link_tree(Pid, Info)
+ --------------------
+
+ Returns a tree which represents a cluster of linked processes.
+ This function receives the initial Pid to start from.
+ The function doesn't recurse to pids older than initial one.
+ The Pids which are lesser than initial Pid are still shown in the output.
+ The info argument is a list of process_info_item() as documented in
+ erlang:process_info/2. We don't do any attempts to prevent dangerous items.
+ Be warn that passing some of them such as `messages` for example
+ can be dangerous in a very busy system.
+ ---
+ ", []);
+help(mapfold_tree) ->
+ io:format("
+ mapfold_tree(Tree, Acc, Fun)
+ -----------------------
+
+ Traverses all nodes of the tree. It is a combination of a map and fold.
+ It calls a user provided callback for every node of the tree.
+ `Fun(Key, Value, Pos, Acc) -> {NewValue, NewAcc}`.
+ Where:
+ - Key of the node (usualy Pid of a process)
+ - Value of the node (usualy information collected by link_tree)
+ - Pos - depth from the root of the tree
+ - Acc - user's accumulator
+
+ ---
+ ", []);
+help(map_tree) ->
+ io:format("
+ map_tree(Tree, Fun)
+ -----------------------
+
+ Traverses all nodes of the tree in order to modify them.
+ It calls a user provided callback
+ `Fun(Key, Value, Pos) -> NewValue`
+ Where:
+ - Key of the node (usualy Pid of a process)
+ - Value of the node (usualy information collected by link_tree)
+ - Pos - depth from the root of the tree
+
+ ---
+ ", []);
+help(fold_tree) ->
+ io:format("
+ fold_tree(Tree, Fun)
+ Traverses all nodes of the tree in order to collect some aggregated
information
+ about the tree. It calls a user provided callback
+ `Fun(Key, Value, Pos) -> NewValue`
+ Where:
+ - Key of the node (usualy Pid of a process)
+ - Value of the node (usualy information collected by link_tree)
+ - Pos - depth from the root of the tree
+
+ ---
+ ", []);
+help(linked_processes_info) ->
+ io:format("
+ linked_processes_info(Pid, Info)
+ --------------------------------
+
+ Convinience function which reduces the amount of typing compared to
direct
Review comment:
Convenience
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