RCR 332: mmap'd version of IO.scan( file_name, regexp)

IO.read( file_name) reads in the entire file into a string.

string.scan( regexp){|match| } scans the entire string for regexp yielding matches.

The limit on doing...

IO.read(file_name).scan( regexp)

is the size of your machines unused physical memory.

Unix has the very handy facility called mmap that allows one to memory map and entire file and the contents of that file appears mapped into your virtual address space.

The operating system handles all the fuss and bother of reading (and forgetting) pages of that file into memory.

Thus is would be very easy to create a mmap'd version, semantically the same as the following function...

 def IO.scan( file_name, regexp, &block)
   IO.read(file_name).scan( regexp, &block)
 end

But being mmap'd could handle files up (almost) up to 4GB in size.

 def IO.scan( file_name, regexp, &block)
  IO.read(file_name).scan( regexp, &block)
 end

to use unix mmap.

Where they do the second mmap and the memcpy, we would do the regexp scan.

So that would have to be mashed together with io_read in io.c and rb_str_scan in string.c