Timer Class

ruby-talk
1

Hai Dude

I want to write one class that class should act as a Timer
On that class , i will check the database every second for database
field called Diaplay_time ,if the current system time matched with
database Display_Time field data then i will show the message in
console,That class should terminate only when i press "Ctrl+C" key
otherwise that wont stop
ok
can any body tell me the solution?
I need to do that
ok
Bye
By
P.S.Hussain

···

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Posted via http://www.ruby-forum.com/.

2

Hussain wrote:

Hai Dude

I want to write one class that class should act as a Timer
On that class , i will check the database every second for database
field called Diaplay_time ,if the current system time matched with
database Display_Time field data then i will show the message in
console,That class should terminate only when i press "Ctrl+C" key
otherwise that wont stop

You can write a very simple while loop for this:

while true do
   start_time = Time.now
   #do database stuff
   total_time = Time.now - start_time
   sleep(1.0 - total_time) # ignoring the possibility of total_time > 1
end

Alternatively, to make it more Rubyish, use a block or two (untested):

def time_block
   start_time = Time.now
   yield
   return Time.now - start_time
end

def repeat_every(seconds)
   while true do
     sleep( seconds - time_block { yield } ) # again ignoring time > seconds
   end
end

Use it like this:

repeat_every(1.0) do
   # do database stuff
end

···

--
Alex

3

In general there are two common approaches:
  - use threads
  - use an event loop

In Ruby, threads are easy to write. To set up a timer using threads,
create a thread that sleeps for one second, wakes up, then does your
check. The disadvantage to this approach is that your code must be
thread-safe.

With an event loop, your code waits for an event (a timer to fire, input
from the user, etc.) and responds to that event. There are numerous
libraries out there to help with this, including Ruby/Event and
IO::Reactor.

Paul

···

On Fri, Apr 27, 2007 at 04:19:18PM +0900, Hussain wrote:

Hai Dude

I want to write one class that class should act as a Timer
On that class , i will check the database every second for database
field called Diaplay_time ,if the current system time matched with
database Display_Time field data then i will show the message in
console,That class should terminate only when i press "Ctrl+C" key
otherwise that wont stop
ok
can any body tell me the solution?
I need to do that

4

Hi Alex,

···

On 4/27/07, Alex Young <alex@blackkettle.org> wrote:

Hussain wrote:
> Hai Dude
>
> I want to write one class that class should act as a Timer
> On that class , i will check the database every second for database
> field called Diaplay_time ,if the current system time matched with
> database Display_Time field data then i will show the message in
> console,That class should terminate only when i press "Ctrl+C" key
> otherwise that wont stop

You can write a very simple while loop for this:

while true do
   start_time = Time.now
   #do database stuff
   total_time = Time.now - start_time
   sleep(1.0 - total_time) # ignoring the possibility of total_time > 1
end

Alternatively, to make it more Rubyish, use a block or two (untested):

def time_block
   start_time = Time.now
   yield
   return Time.now - start_time
end

def repeat_every(seconds)
   while true do
     sleep( seconds - time_block { yield } ) # again ignoring time > seconds
   end
end

After seeing this code, I thought, how we can make this reentrant.
Here is what I could come up with.
------
def time_block
  start_time = Time.now
  Thread.new { yield }
  Time.now - start_time
end

def repeat_every(seconds)
  while true do
    time_spent = time_block { yield } # To handle -ve sleep interaval
    sleep(seconds - time_spent) if time_spent < seconds
  end
end

repeat_every(1) {
  puts "Task started. #{Time.now}"
  sleep(2)
  puts "Task done. #{Time.now}"
}
------

What precautions should one take in such code involving threads and sleep?

Use it like this:

repeat_every(1.0) do
   # do database stuff
end

--
Alex

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