class ActionDispatch::DebugLocks
This middleware can be used to diagnose deadlocks in the autoload interlock.
To use it, insert it near the top of the middleware stack, using config/application.rb
:
config.middleware.insert_before Rack::Sendfile, ActionDispatch::DebugLocks
After restarting the application and re-triggering the deadlock condition, /rails/locks
will show a summary of all threads currently known to the interlock, which lock level they are holding or awaiting, and their current backtrace.
Generally a deadlock will be caused by the interlock conflicting with some other external lock or blocking I/O call. These cannot be automatically identified, but should be visible in the displayed backtraces.
NOTE: The formatting and content of this middleware's output is intended for human consumption, and should be expected to change between releases.
This middleware exposes operational details of the server, with no access control. It should only be enabled when in use, and removed thereafter.
Public Class Methods
# File lib/action_dispatch/middleware/debug_locks.rb, line 26 def initialize(app, path = "/rails/locks") @app = app @path = path end
Public Instance Methods
# File lib/action_dispatch/middleware/debug_locks.rb, line 31 def call(env) req = ActionDispatch::Request.new env if req.get? path = req.path_info.chomp("/") if path == @path return render_details(req) end end @app.call(env) end
Private Instance Methods
# File lib/action_dispatch/middleware/debug_locks.rb, line 103 def blocked_by?(victim, blocker, all_threads) return false if victim.equal?(blocker) case victim[:sleeper] when :start_sharing blocker[:exclusive] || (!victim[:waiting] && blocker[:compatible] && !blocker[:compatible].include?(false)) when :start_exclusive blocker[:sharing] > 0 || blocker[:exclusive] || (blocker[:compatible] && !blocker[:compatible].include?(victim[:purpose])) when :yield_shares blocker[:exclusive] when :stop_exclusive blocker[:exclusive] || victim[:compatible] && victim[:compatible].include?(blocker[:purpose]) && all_threads.all? { |other| !other[:compatible] || blocker.equal?(other) || other[:compatible].include?(blocker[:purpose]) } end end
# File lib/action_dispatch/middleware/debug_locks.rb, line 45 def render_details(req) threads = ActiveSupport::Dependencies.interlock.raw_state do |raw_threads| # The Interlock itself comes to a complete halt as long as this block # is executing. That gives us a more consistent picture of everything, # but creates a pretty strong Observer Effect. # # Most directly, that means we need to do as little as possible in # this block. More widely, it means this middleware should remain a # strictly diagnostic tool (to be used when something has gone wrong), # and not for any sort of general monitoring. raw_threads.each.with_index do |(thread, info), idx| info[:index] = idx info[:backtrace] = thread.backtrace end raw_threads end str = threads.map do |thread, info| if info[:exclusive] lock_state = +"Exclusive" elsif info[:sharing] > 0 lock_state = +"Sharing" lock_state << " x#{info[:sharing]}" if info[:sharing] > 1 else lock_state = +"No lock" end if info[:waiting] lock_state << " (yielded share)" end msg = +"Thread #{info[:index]} [0x#{thread.__id__.to_s(16)} #{thread.status || 'dead'}] #{lock_state}\n" if info[:sleeper] msg << " Waiting in #{info[:sleeper]}" msg << " to #{info[:purpose].to_s.inspect}" unless info[:purpose].nil? msg << "\n" if info[:compatible] compat = info[:compatible].map { |c| c == false ? "share" : c.to_s.inspect } msg << " may be pre-empted for: #{compat.join(', ')}\n" end blockers = threads.values.select { |binfo| blocked_by?(info, binfo, threads.values) } msg << " blocked by: #{blockers.map { |i| i[:index] }.join(', ')}\n" if blockers.any? end blockees = threads.values.select { |binfo| blocked_by?(binfo, info, threads.values) } msg << " blocking: #{blockees.map { |i| i[:index] }.join(', ')}\n" if blockees.any? msg << "\n#{info[:backtrace].join("\n")}\n" if info[:backtrace] end.join("\n\n---\n\n\n") [200, { "Content-Type" => "text/plain", "Content-Length" => str.size }, [str]] end