Module: Bluepill::System

Extended by:
System
Included in:
System
Defined in:
lib/bluepill/system.rb

Overview

This class represents the system that bluepill is running on.. It’s mainly used to memoize results of running ps auxx etc so that every watch in the every process will not result in a fork

Constant Summary collapse

APPEND_MODE = 
"a"
IDX_MAP =

The position of each field in ps output

{
  :pid => 0,
  :ppid => 1,
  :pcpu => 2,
  :rss => 3
}

Instance Method Summary collapse

Instance Method Details

#can_write_pid_file(pid_file, logger) ⇒ Object 



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# File 'lib/bluepill/system.rb', line 201

def can_write_pid_file(pid_file, logger)
  FileUtils.touch(pid_file)
  File.unlink(pid_file)
  return true
  
rescue Exception => e
  logger.warning "%s - %s" % [e.class.name, e.message]
  e.backtrace.each {|l| logger.warning l}
  return false
end

#cpu_usage(pid) ⇒ Object 



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# File 'lib/bluepill/system.rb', line 27

def cpu_usage(pid)
  ps_axu[pid] && ps_axu[pid][IDX_MAP[:pcpu]].to_f
end

#daemonize(cmd, options = {}) ⇒ Object

Returns the pid of the child that executes the cmd



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# File 'lib/bluepill/system.rb', line 44

def daemonize(cmd, options = {})
  rd, wr = IO.pipe

  if child = Daemonize.safefork
    # we do not wanna create zombies, so detach ourselves from the child exit status
    ::Process.detach(child)
    
    # parent
    wr.close
    
    daemon_id = rd.read.to_i
    rd.close
      
    return daemon_id if daemon_id > 0
    
  else
    # child
    rd.close

    drop_privileges(options[:uid], options[:gid])
    
    # if we cannot write the pid file as the provided user, err out
    exit unless can_write_pid_file(options[:pid_file], options[:logger])
    
    to_daemonize = lambda do
      # Setting end PWD env emulates bash behavior when dealing with symlinks
      Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
      
      redirect_io(*options.values_at(:stdin, :stdout, :stderr))
      
      ::Kernel.exec(cmd)
      exit
    end

    daemon_id = Daemonize.call_as_daemon(to_daemonize, nil, cmd)
            
    File.open(options[:pid_file], "w") {|f| f.write(daemon_id)}
    
    wr.write daemon_id        
    wr.close

    exit
  end
end

#drop_privileges(uid, gid) ⇒ Object

be sure to call this from a fork otherwise it will modify the attributes of the bluepill daemon



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# File 'lib/bluepill/system.rb', line 192

def drop_privileges(uid, gid)
  uid_num = Etc.getpwnam(uid).uid if uid
  gid_num = Etc.getgrnam(gid).gid if gid

  ::Process.groups = [gid_num] if gid
  ::Process::Sys.setgid(gid_num) if gid
  ::Process::Sys.setuid(uid_num) if uid
end

#execute_blocking(cmd, options = {}) ⇒ Object

Returns the stdout, stderr and exit code of the cmd



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# File 'lib/bluepill/system.rb', line 90

def execute_blocking(cmd, options = {})
  rd, wr = IO.pipe
  
  if child = Daemonize.safefork
    # parent
    wr.close
    
    cmd_status = rd.read
    rd.close
    
    ::Process.waitpid(child)
    
    return Marshal.load(cmd_status)
    
  else
    # child
    rd.close
    
    # create a child in which we can override the stdin, stdout and stderr
    cmd_out_read, cmd_out_write = IO.pipe
    cmd_err_read, cmd_err_write = IO.pipe
    
    pid = fork {
      # grandchild
      drop_privileges(options[:uid], options[:gid])
      
      Dir.chdir(ENV["PWD"] = options[:working_dir]) if options[:working_dir]
      
      # close unused fds so ancestors wont hang. This line is the only reason we are not
      # using something like popen3. If this fd is not closed, the .read call on the parent
      # will never return because "wr" would still be open in the "exec"-ed cmd
      wr.close

      # we do not care about stdin of cmd
      STDIN.reopen("/dev/null")

      # point stdout of cmd to somewhere we can read
      cmd_out_read.close
      STDOUT.reopen(cmd_out_write)
      cmd_out_write.close

      # same thing for stderr
      cmd_err_read.close
      STDERR.reopen(cmd_err_write)
      cmd_err_write.close

      # finally, replace grandchild with cmd
      ::Kernel.exec(cmd)
    }

    # we do not use these ends of the pipes in the child
    cmd_out_write.close
    cmd_err_write.close
    
    # wait for the cmd to finish executing and acknowledge it's death
    ::Process.waitpid(pid)
    
    # collect stdout, stderr and exitcode
    result = {
      :stdout => cmd_out_read.read,
      :stderr => cmd_err_read.read,
      :exit_code => $?.exitstatus
    }

    # We're done with these ends of the pipes as well
    cmd_out_read.close
    cmd_err_read.close
    
    # Time to tell the parent about what went down
    wr.write Marshal.dump(result)
    wr.close

    exit  
  end
end

#get_children(parent_pid) ⇒ Object 



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# File 'lib/bluepill/system.rb', line 35

def get_children(parent_pid)
  returning(Array.new) do |child_pids|
    ps_axu.each_pair do |pid, chunks| 
      child_pids << chunks[IDX_MAP[:pid]].to_i if chunks[IDX_MAP[:ppid]].to_i == parent_pid.to_i
    end
  end
end

#memory_usage(pid) ⇒ Object 



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# File 'lib/bluepill/system.rb', line 31

def memory_usage(pid)
  ps_axu[pid] && ps_axu[pid][IDX_MAP[:rss]].to_f
end

#pid_alive?(pid) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bluepill/system.rb', line 18

def pid_alive?(pid)
  begin
    ::Process.kill(0, pid)
    true
  rescue Errno::ESRCH
    false
  end
end

#ps_axu ⇒ Object 



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# File 'lib/bluepill/system.rb', line 174

def ps_axu
  # TODO: need a mutex here
  store[:ps_axu] ||= begin
    # BSD style ps invocation
    lines = `ps axo pid=,ppid=,pcpu=,rss=`.split("\n")

    lines.inject(Hash.new) do |mem, line| 
      chunks = line.split(/\s+/)
      chunks.delete_if {|c| c.strip.empty? }
      pid = chunks[IDX_MAP[:pid]].strip.to_i
      mem[pid] = chunks
      mem
    end
  end
end

#redirect_io(io_in, io_out, io_err) ⇒ Object 



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# File 'lib/bluepill/system.rb', line 212

def redirect_io(io_in, io_out, io_err)
  $stdin.reopen(io_in) if io_in
  
  if !io_out.nil? && !io_err.nil? && io_out == io_err
    $stdout.reopen(io_out, APPEND_MODE)
    $stderr.reopen($stdout)
    
  else
    $stdout.reopen(io_out, APPEND_MODE) if io_out
    $stderr.reopen(io_err, APPEND_MODE) if io_err
  end
end

#reset_data ⇒ Object 



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# File 'lib/bluepill/system.rb', line 170

def reset_data
  store.clear unless store.empty?
end

#store ⇒ Object 



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# File 'lib/bluepill/system.rb', line 166

def store
  @store ||= Hash.new
end