From: jcb@... (MetalOne)
Date: 2002-11-17T08:46:18+09:00
Subject: Not really a ruby question, but this is a smart group.  Win32 file.write timing.

I am trying to write non-compressed video to a file at 40 fps.
My write times under Win32 are highly erratic.
The following ruby script will demonstrate this.
I have the same problem in C++, with the Win32 APIs, so it is not a
Ruby issue.

The script does the following:
1) Writes 4000 frames at 640x240.  614MB total. Each frame is just a
bunch of zeroes.
2) Times each frame write.
3) Writes a log file, listing the time for each frame and the
corresponding
frame number.  The file is in descending order of write times.

Observations:
For my computer system(866Mhz PIII, 100 ATA IDE drive), the log file
will show write times between less than 10ms and greater than 150ms.
In C++ using tick counts I see writes between 1.5ms and 160ms.

I don't understand the reason for the huge timing difference.
I have tried defragging the drive first.
I have even tried overwriting an existing file, after defragging.
Is this just the nature of drives, does seek time kill me?
Still seek + latency should be around 10ms + 5ms?  Way less than
150ms.
Do the Win32 write API's suck?

Here is the script.
Could somebody run it on a Linux box and report, whether it has the
same issue.

#####################################
#dummy data for the frame to write
s = '0'*640*240

# A nested list of [frameNo, usecs to write frame]
l = []

timeStart = Time.new
File.open("test.dat", "w") do |file|
	4000.times do |frameNo|
		t0 = Time.new
		file.write s
		tdelta = Time.at(Time.new - t0)
		l << [frameNo, tdelta.usec]
	end
end
timeEnd = Time.new
timeDelta = Time.at(timeEnd-timeStart)
puts "total time: #{timeDelta.min}:#{timeDelta.sec}.#{timeDelta.usec}"

#sort the list using usecs descending
sortedList = l.sort { |a,b| b[1] <=> a[1] }
File.open("log.txt", "w") do |logfile|
	sortedList.each { |frameNo, usecs| logfile.puts "#{usecs}:
#{frameNo}" }
end