Issue #3917 has been updated by ko1 (Koichi Sasada).

Description updated
Status changed from Assigned to Feedback

I made caller_locations() (see [ruby-core:45253] [RFC] RubyVM::FrameInfo.caller method).

Maybe the last problem is naming of this method.



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Feature #3917: [proposal] called_from() which is much faster than caller()
https://bugs.ruby-lang.org/issues/3917#change-27431

Author: kwatch (makoto kuwata)
Status: Feedback
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: core
Target version: 2.0.0


=begin
 I propose to introduce Kernel#called_from() which is similar to caller()
 but much faster than it.
 
 
 Background
 ----------
 
 There are some cases to want to know from where current method is called.
 In this case, Kernel#caller() is used.
 
 But Kernel#caller() has performance issues for these cases.
 
 * caller() retrieves entire stack frame. It is too heavy.
 * caller() returns an array of "filename:linenum in `method'" string.
   User must parse it and retrieve filename and linenum by rexp.
   It is also very heavy weight task.
 
 Therefore I propose Kernel#called_from() which is very light weight
 compared to caller(). A certain benchmark shows that called_from()
 is more than 20 times faster tan caller().
 
 ???????????????????????????????????????????????????????????????????????????
 ????????????????????? Kernel#caller() ???使??????????
 
 ????????? Kernel#caller() ??????????????????????????????????????????常???????
 
 * caller() ??????????????????????????????????????????????常?????????????
 * caller() ??? "?????????:???? in `???????????'" ???????????????????????????????
   ?????正覨??使????????????????????????????????????????????????????
   ??????????????????????
 
 ?????????????Kernel#called_from() ???追????????????????????????????
 ??????????????? caller() ?????????常???????軽????????????????????
 called_from() ??? caller() ????????20???以?????????
 
 
 Spec
 -----
 
 call-seq:
    called_from(start=1)    -> array or nil
 
 Returns file name, line number, and method name of the stack.
 The optional _start_ parameter represents the number of stack
 entries to skip.
 
 Returns +nil+ if _start_ is greater than the size of
 current execution stack.
 
 Raises ArgumentError if _start_ is negative value.
 
 
 Example code
 ------------
 
   # example.rb
    1:  def f1()
    2:    f2()
    3:  end
    4:  def f2()
    5:    f3()
    6:  end
    7:  def f3()
    8:    p called_from()    #=> ["example.rb", 5, "f2"]
    9:    p called_from(0)   #=> ["example.rb", 9, "f3"]
   10:    p called_from(1)   #=> ["example.rb", 5, "f2"]
   11:    p called_from(2)   #=> ["example.rb", 2, "f1"]
   12:    p called_from(3)   #=> ["example.rb", 15, "<main>"]
   13:    p called_from(4)   #=> nil
   14:  end
   15:  f1()
 
 
 Use Case
 --------
 
 Case 1: logging method
 
   def log_info(message)
     filename, linenum, _ = called_from()   # !!!
     @logger.info "#{filename}:#{linenum}: #{message}"
   end
 
 
 Case 2: debug print
 
   def debug(message)
     filename, linenum, _ = called_from()   # !!!
     $stderr.puts "*** DEBUG: #{filename}:#{linenum}: #{message}"
   end
 
 
 Case 3: deprecation message
 
   def send(*args)
     filename, linenum, _ = called_from()   # !!!
     msg = "`send()' is deprecated. use `__send__()' instead."
     msg << " (file: #{filename}, line: #{linenum})"
     $stderr.puts "*** warning: #{msg}"
     __send__(*args)
   end
 
 
 Case 4: ActiveSupport::Testing::Pending
 
   module ActiveSupport::Testing::Peding
     def pending(description = "", &block)
         :
       #caller[0] =~ (/(.*):(.*):in `(.*)'/)             # original
       #@@pending_cases << "#{$3} at #{$1}, line #{$2}"  # original
       #print "P"                                        # original
       filenemae, linenum, method = called_from()    # !!!
       @@pending_cases << "#{method} at #{filename}, line #{linenum}"
       print "P"
         :
     end
   end
 
 
 Case 5: activesupport/lib/active_support/core_ext/module/delegation.rb
 
   class Module
     def delegate(*methods)
         :
       #file, line = caller.first.split(':', 2)  # original
       #line = line.to_i                         # original
       file, line, _ = called_from()             # !!!
         :
       module_eval(<<-EOS, file, line - 5)
         :
     end
   end
 
 
 Case 6: caching helper for template system
 
   def cache_with(key)
     data, created_at = @_cache_store.get(key)
     filename, = called_from()   # !!!
     ## if template file is newer than cached data then clear cache.
     ## (performance is very important in this case.)
     if created_at < File.mtime(filename)
       data = nil
       @_cache_store.del(key)
     end
     ##
     if data.nil?
       len = @_buf.length
       yield
       data = @_buf[len..-1]
       @_cache_store.set(key, data)
     else
       @_buf << data
     end
     nil
   end
   
   ## in template file
   <% cache_with("orders/#{@order.id}") do %>
     <p>Order ID: <%=h @order.id %></p>
     <p>Customer: <%=h @order.customer.name %></p>
   <% end %>
 
 
 Benchmark
 ---------
 
 Attached benchmark shows that called_from() is much faster than caller().
 This is very important for logging or template timestamp check.
 
     $ ./ruby -s bench.rb -N=100000
                                         user     system      total        real
     caller()[0]                     1.890000   0.010000   1.900000 (  1.941812)
     caller()[0] (retrieve)          2.190000   0.010000   2.200000 (  2.225966)
     called_from()                   0.100000   0.000000   0.100000 (  0.102810)
     called_from() (retrieve)        0.100000   0.000000   0.100000 (  0.102133)
 
 
 Another Solutions
 -----------------
 
 Adding new gobal function may be refused.
 The followings are another solutions instead of new global function.
 
 * Extend caller() to take 'count' parameter.
   For example:
 
     start = 1
     count = 1
     caller(start, count)  #=> ["filename:linenum in `method'"]
 
 * Extend caller() to take 'conbine' flag.
   For example:
 
     start = 1
     count = nil
     conbine = false
     caller(start, count, conbine)
                          #=> [["filename", linenum, "method"],
 			 #    ["filename", linenum, "method"],
 			 #    .... ]
 
 * Add new standard library 'called_from.so' instead of Kernel#called_from().
 
 ??????????????????????????????絶????????????????????
 ????????????caller()?????張??????called_from()????????????????????????????
 ????????????????????????????????
 ???????????? Kernel#called_from() ????????? called_from.so ?????添??
 ???????????????????????
 
 
 Note
 ----
 
 * I tried to implement the above solutions, but failed because
   vm_backtrace_each() seems to search stack frames in the reverse
   order of what called_from() requires.
 
 * I can implement called_from() as user library in Ruby 1.8.
   http://rubygems.org/gems/called_from
   It is allowed to access to stack frame in Ruby 1.8, but no in 1.9.
   This is why I submit this propose.
 
 * ?????????another solutions???????????????????????????called_from() ????
   ?????????????????????????辿???????????対??????vm_backtrace_each() ???
   ??????????辿??????????????????????????????????????諦????????
 
 * Ruby 1.8 ????張?????????????????????????????????????????
   ?????????????????????????
   http://rubygems.org/gems/called_from
   ??????1.9????????????????????????????????????????????????
   ??????????????????????????????????????????????????????
=end



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