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module Gitlab
module Metrics
# Module for instrumenting methods.
#
# This module allows instrumenting of methods without having to actually
# alter the target code (e.g. by including modules).
#
# Example usage:
#
# Gitlab::Metrics::Instrumentation.instrument_method(User, :by_login)
module Instrumentation
SERIES = 'method_calls'
PROXY_IVAR = :@__gitlab_instrumentation_proxy
def self.configure
yield self
end
# Instruments a class method.
#
# mod - The module to instrument as a Module/Class.
# name - The name of the method to instrument.
def self.instrument_method(mod, name)
instrument(:class, mod, name)
end
# Instruments an instance method.
#
# mod - The module to instrument as a Module/Class.
# name - The name of the method to instrument.
def self.instrument_instance_method(mod, name)
instrument(:instance, mod, name)
end
# Recursively instruments all subclasses of the given root module.
#
# This can be used to for example instrument all ActiveRecord models (as
# these all inherit from ActiveRecord::Base).
#
# This method can optionally take a block to pass to `instrument_methods`
# and `instrument_instance_methods`.
#
# root - The root module for which to instrument subclasses. The root
# module itself is not instrumented.
def self.instrument_class_hierarchy(root, &block)
visit = root.subclasses
until visit.empty?
klass = visit.pop
instrument_methods(klass, &block)
instrument_instance_methods(klass, &block)
klass.subclasses.each { |c| visit << c }
end
end
# Instruments all public methods of a module.
#
# This method optionally takes a block that can be used to determine if a
# method should be instrumented or not. The block is passed the receiving
# module and an UnboundMethod. If the block returns a non truthy value the
# method is not instrumented.
#
# mod - The module to instrument.
def self.instrument_methods(mod)
mod.public_methods(false).each do |name|
method = mod.method(name)
if method.owner == mod.singleton_class
if !block_given? || block_given? && yield(mod, method)
instrument_method(mod, name)
end
end
end
end
# Instruments all public instance methods of a module.
#
# See `instrument_methods` for more information.
#
# mod - The module to instrument.
def self.instrument_instance_methods(mod)
mod.public_instance_methods(false).each do |name|
method = mod.instance_method(name)
if method.owner == mod
if !block_given? || block_given? && yield(mod, method)
instrument_instance_method(mod, name)
end
end
end
end
# Returns true if a module is instrumented.
#
# mod - The module to check
def self.instrumented?(mod)
mod.instance_variable_defined?(PROXY_IVAR)
end
# Returns the proxy module (if any) of `mod`.
def self.proxy_module(mod)
mod.instance_variable_get(PROXY_IVAR)
end
# Instruments a method.
#
# type - The type (:class or :instance) of method to instrument.
# mod - The module containing the method.
# name - The name of the method to instrument.
def self.instrument(type, mod, name)
return unless Metrics.enabled?
name = name.to_sym
target = type == :instance ? mod : mod.singleton_class
if type == :instance
target = mod
label = "#{mod.name}##{name}"
method = mod.instance_method(name)
else
target = mod.singleton_class
label = "#{mod.name}.#{name}"
method = mod.method(name)
end
unless instrumented?(target)
target.instance_variable_set(PROXY_IVAR, Module.new)
end
proxy_module = self.proxy_module(target)
# Some code out there (e.g. the "state_machine" Gem) checks the arity of
# a method to make sure it only passes arguments when the method expects
# any. If we were to always overwrite a method to take an `*args`
# signature this would break things. As a result we'll make sure the
# generated method _only_ accepts regular arguments if the underlying
# method also accepts them.
if method.arity == 0
args_signature = '&block'
else
args_signature = '*args, &block'
end
proxy_module.class_eval <<-EOF, __FILE__, __LINE__ + 1
def #{name}(#{args_signature})
trans = Gitlab::Metrics::Instrumentation.transaction
if trans
start = Time.now
retval = super
duration = (Time.now - start) * 1000.0
if duration >= Gitlab::Metrics.method_call_threshold
trans.increment(:method_duration, duration)
trans.add_metric(Gitlab::Metrics::Instrumentation::SERIES,
{ duration: duration },
method: #{label.inspect})
end
retval
else
super
end
end
EOF
target.prepend(proxy_module)
end
# Small layer of indirection to make it easier to stub out the current
# transaction.
def self.transaction
Transaction.current
end
end
end
end
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