// The last time a signal was processed
// Initialized to DateTime.MinValue so the first signal received
// will not be lost
DateTime LastSignalTime = DateTime.MinValue;

// Lock object to prevent re-entrancy
object SignalLock = new object();

// Minimum time between invocations
static readonly TimeSpan MinimumTime = TimeSpan.FromSeconds(1.0);

void SignalReceived(SomeObject dataObject)
{
    if (!Monitor.TryEnter(SignalLock))
    {
        // Currently processing. Exit.
        return;
    }
    try
    {
        if ((DateTime.Now - LastSignalTime) < MinimumTime)
        {
            // Already processed within the last second.
            return;
        }
        // ...
        // do processing here
        // ...
        // And then save the last signal time.
        LastSignalTime = DateTime.Now;
    }
    finally
    {
        Monitor.Exit(SignalLock);
    }
}

That looks reasonable. I covered all the bases, protecting the processing with a Monitor to prevent re-entrant use, and checking the time to ensure that I don’t process a signal more often than once per second.

There’s only one problem. The program assumes that DateTime.Now will increase by one second for every wall clock second. This code does not take into account Daylight Saving Time changes, changes caused by updating with an NTP service, or the user resetting the clock. If one of those events occurs, things fall apart.

For example, when we set the clocks ahead in the spring, this code could process twice in a very short period of time. Imagine that you processed a signal at 01:59:59.800. 200 milliseconds later, the time will be 03:00:00.000. Your code would then process another signal, even though less than one second has passed.

It’s worse when the time is set back in the fall. Say you process a signal at 01:59:59.100. 900 milliseconds after that, the time is changed to 01:00:00.000, and it will be another hour before the code does any more processing.

You can avoid those DST errors by using DateTime.UtcNow in place of DateTime.Now, but that won’t solve the problem that occurs with NTP or user-initiated time changes.

The problem here is that your code is depending on the system clock, which the program doesn’t control. The clock can change at any time, and if you depend on it for critical processing you’re going to be sorry.

You can remove that dependency by using a Stopwatch, which measures elapsed time independent of the system clock. In the code below, I initialize a Stopwatch when the program starts. I’ve modified the logic slightly to save a NextSignalTime, which represents the time when another signal can be processed.

// The amount of time elapsed since the program started
static readonly Stopwatch ProgramTimer = Stopwatch.StartNew();

// The next time a signal can be processed.
TimeSpan NextSignalTime = TimeSpan.Zero;

// Lock object to prevent re-entrancy
object SignalLock = new object();

// Minimum time between invocations
static readonly TimeSpan MinimumTime = TimeSpan.FromSeconds(1.0);

void SignalReceived(SomeObject dataObject)
{
    if (!Monitor.TryEnter(SignalLock))
    {
        // Currently processing. Exit.
        return;
    }
    try
    {
        if (ProgramTimer.Elapsed < NextSignalTime)
        {
            // Already processed within the last second.
            return;
        }
        // ...
        // do processing here
        // ...
        // And then save the next signal time.
        NextSignalTime = ProgramTimer.Elapsed + MinimumTime;
    }
    finally
    {
        Monitor.Exit(SignalLock);
    }
}

This code can’t be affected by system time changes because it doesn’t depend on the system time.

You don’t control the system clock. Don’t depend on it for measuring elapsed time. It’s fine to depend on it to tell you what time of day it is. If the user changes his clock, that’s his problem. But you can’t be at the mercy of the system clock if you want accurate elapsed time measurements.

The Spring Round-Up does not feature a show or any real “public” appeal. The general public is welcome to come in and look around, of course, but there are no tables set up with pieces on display, and there is no judged contest. The judged show takes place in the fall–typically the last week of September or first week of October.

I had two goals for my trip: to participate in the Whittlin’ Contest, and to buy some tools. I’m decidedly not a tool junkie, but I’ve been carving for three years with just a knife (okay, I own a handful of knives), one V-tool, and one gouge. There are things I can’t do (or can’t do easily) with those few tools, so I thought I’d pick up a few other gouges. I could have ordered the tools online, but wanted some advice from more experienced carvers, and the ability to hold the tools in my hand before I shelled out money for them. I ended up with six new gouges and a few new power carving bits, all of which should help me improve my carving.

I spent Tuesday afternoon wandering around the floor, briefly watching and listening to the classes that were taking place, talking to other carvers, and generally having a good ol’ wood nerd time. I also spent a little time in the Carving Corner, whittling a little dog and chatting with other carvers. Once again I was struck by how friendly and inclusive carvers are. Every carver there, from those who are just starting out to the most accomplished, were happy to sit around and chat while whittling away on a project. And they’re happy to answer questions and spend their time demonstrating some technique or other. Whittling with this group is a relaxing and entertaining experience.

The Whittlin’ Contest was scheduled for 7:00 PM. There are three classes: Novice, Intermediate, and Open. There are a few set rules, the most important being that if you win in one of the lower classes, you have to move up. Beyond that, the person in charge of the contest (who, by tradition, is the person who won the Open class the year before) sets the other rules.

Because I had never done this before, I entered into the Novice class. There were five of us in Novice, five or six in Intermediate, and almost a dozen in the Open class. We all sat down at our respective tables and they passed out the wood. The Novices got a block of basswood, 2-1/2″ x 2-1/2″ x 3″. They told us to carve a “Civil War hat,” further clarified as “any kind of hat you would have seen during the Civil War.”

The Intermediates were given a piece that was approximately 8 inches long, and cut in to a triangle that was about 2″ on a side. I think their instructions were to carve “a military scene.” The Open contestants were given a block about 2-1/2 inches square and maybe six inches tall, and told to carve “a Civil War caricature.”

We Novices were told that we could use any tool in our toolbox. The Intermediates were limited to, I think, three tools, and those in the Open category could use only one knife. They told us that we had an hour, and started the clock.

I don’t know much about hats in general, and I know even less about the kinds of hats worn during the Civil War. I could picture the Confederate cap, but not well enough to try carving one without a reference. But I figured that I could do a cowboy hat. Certainly somebody during that time was wearing cowboy hats. The only problem was that I had to remove a whole lot of wood to realize my vision.

At one point, after I made a mistake and broke the brim of what I was working on, I considered changing to a stovepipe hat, but I ended up having enough time left over to make it look kind of like a cowboy hat.

Judging is done based on originality, technical quality (proportion, symmetry, clean cuts, etc.), and also on completeness. Somebody told me that completing the project within the time allotted was worth a lot in the judges’ eyes. I had carved a couple of stovepipe hats before, and one (failed) cowboy hat, so I was pretty sure I could finish this project in an hour.

I did finish it in an hour, and although it’s a bit of a goofy looking hat, I ended up winning first place in the Novice category. Here’s my hat along with the second and third place winners.

I think that either of the other two would have beat mine, had the carvers finished them in time.  My hat is two inches tall, and the brim is two inches in diameter. Here’s a closer picture.

I was going to show the Intermediate and Open winners, as well, but the pictures were very blurry.

My prize was a plaque:

I’ll be the first to admit that my hat is no great carving. But then, I was under pressure just to finish something in the allotted time. Given advanced notice and unlimited time, I could do a much better hat.

I honestly was very surprised to win this little contest. But now I have to move up to Intermediate, and that’s going to require a lot of practice. Even the worst of the Intermediate entries was beyond my current skills.

I’ve been saying for the last month that I’m going to get back on the bike, but I’ve been putting it off. This morning I got frustrated with the program I was working on, and decided to take a ride and clear my head. An hour on the bike usually does.

Every time I come back to cycling after a long absence, I unable to understand how I could possibly have stopped. That first few miles feels so good: back out on the road, enjoying the fresh air and the wind in my face, nothing heavy on my mind. It’s very liberating.

It hurts, of course. My legs aren’t used to climbing even the smallest hills. But I know that within a couple of weeks the pain will be gone and I’ll feel a lot better. I just can’t understand how I could have stopped riding again.

I took an experimental loop through a new subdivision and was on my way home when I saw a large group of riders–perhaps as many as 50–coming up on the other side of the road. There were two motorcycles in front, obviously part of the ride, and three vans following. One of the vans said, “Ride 2 Recovery” on it, and “Wounded Veterans Ahead.”

I had to go see what that was all about.

I turned around, sprinted past the vans, and caught up with the riders. I struck up a conversation with one of the riders, a former Army Ranger from Albuquerque, NM. They’re participating in the Texas Challenge: a 6-day ride from San Antonio to Arlington. The riders raise money to help support the programs that Ride 2 Recovery sponsors. I talked to this guy for a few more minutes, then rode up the line offering encouragement before turning around and heading home.

Had I been in better shape, I probably would have stayed with them all the way to Fort Hood, and then found a ride back somehow. But I figured that 50 miles was probably a bit too far for my first ride after over a year of not riding seriously.

“The Ride 2 Recovery,” the web site says, “is produced by the Fitness Challenge Foundation, (501C3) in partnership with the Military and VA Volunteer Service Office, to benefit Mental and Physical Rehabilitation Programs for our country’s wounded veterans that feature cycling as the core activity.”

Call it fate, coincidence, serendipity, whatever. The likelihood of me running into a group of riders on a Wednesday morning, out on the back roads on my first ride of the season is pretty low. But then, improbable events happen quite frequently. After all, people do win the lottery. Whatever the reason, or even if there was no reason, I sure am glad I encountered this group today. That’s some serious motivation.

I just happen to have a whole lot of bark from an oak tree . . .

As I said, the piece is unfinished. I’ve sanded and finished the dolphin carvings, but the oak bark is still raw. I’ll have to put something on the bark so that it won’t flake off and deteriorate over time.

I realize that neither of the dolphin carvings is especially good. I goofed on the back of the walnut piece–making it too straight and too thin. And I didn’t round the front of the mahogany dolphin very well. That one’s dorsal fin is too small, too. That’s not my fault. The person who gave me the blank had cut it a bit short.

That said, I rather like the idea of using bark as a substitute ocean surface. What do you think?

Here’s another view, closer up.

The piece is a wall hanging, about nine inches tall on the right side, and about two and a half inches wide. Don’t know yet where I’ll hang it.

This is the second “flat back” I’ve carved. I did the other one about two years ago. I also carved a larger whimsical house in a class back in October of 2010.

I like carving the cottonwood bark. The only real problem is that I have to buy the stuff! I might have to find a good supplier, though, and stock up. These things are addictive.