Standard algorithms and boost::ptr_vector

I did something bad the other day.

OK, I can't tell if it was bad. In another environment, it would have been bad, but since this was C++, perhaps it was OK. I was in the situation where I had a boost::ptr_vector, and I wanted to use a standard algorithm on it. Specifically, I wanted to use std::partition to separate the objects that were still "alive" from those that were "dead" (where alive and dead are domain concepts in our application). The complexity here is that ptr_vector is a crazy container.

Most containers deal with a specific type T. You add Ts to the container. Dereferencing an iterator gives you a T&. It's generally assumed that a container operates on a single type, and the standard algorithms make this assumption.

The ptr_vector, on the other hand, appears to be two containers at once. Semantically, it's analogous to a std::vector<managed_ptr_type<T> >. It is intended that, by adding a pointer to the ptr_vector, the ptr_vector takes ownership of the lifetime of the memory at the end of the pointer. So, it is a container of pointers. On the other hand, when iterating a ptr_vector, it appears that it is a container of Ts.

In my case, I wanted to rearrange my ptr_vector. In particular, I wanted to partition the pointers into those whose object was still "alive", and those whose object was "dead". Since a ptr_vector is semantically a container of pointers, it made sense that I should apply std::partition to the ptr_vector. However, ptr_vector::iterator removes a level of indirection: instead of iterating T*, it iterates T&.

In fact, ptr_vector doesn't seem to provide any ways to rearrange the pointers once they are put into the container. Sure, you can mutate the object on the end of the pointer. You could operate at that level. But there doesn't appear to be a safe way to treat the ptr_vector as a container of pointers.

Fortunately, ptr_vector provides a back door. Its iterators support a base() method, which will return an iterator over T* (instead of an iterator over T&). This allows us to treat the ptr_vector as a container of pointers, and to use standard algorithms to manipulate those pointers. Now, this is not without peril. While it seems to be OK to rearrange the pointers, it wouldn't be safe to change the set of pointers. I wouldn't trust using something like std::remove_if, because it might leave garbage in the container after it is done. The container might contain duplicate pointers. Some pointers might get dropped completely. If the container then goes out of scope, it will try to delete these pointers multiple times, which would be a bad thing. It might also fail to delete some pointers, because they were overwritten (and not preserved elsewhere in the container).

This whole thing felt like the best solution possible, while at the same time leaving a lot to be desired. I felt like I was violating the encapsulation of the ptr_vector. I suppose this is one of those cases for which they put in the base() methods on the iterators. Additionally, I don't see any clear way that they could do better. For example, I think an assumption of ptr_vector is that a given pointer only occurs inside it at most once. The standard algorithms don't necessarily respect this assumption; see my commentary on remove_if in the previous paragraph. The standard algorithms, in some cases, expect more freedom than ptr_vector can provide. This disconnect is unfortunate, but not without reason.

An important first step to helping with this problem would be to add methods to ptr_vector (and its siblings) that allow you to treat it as a container of pointers. You could add, remove, and re-arrange the container using these methods. In addition, they could maybe provide specializations of some of the standard algorithms for each container. This is difficult for third party developers to do, since the actual type of a ptr_vector::iterator is implementation defined. The boost guys can cleanly provide a specialization of std::partition for this kind of iterator, but I can't. Now, this isn't perfect. It would help with the standard algorithms, but not third-party algorithms. Still, it would be a great step in the right direction.

So, did I do something bad, or did I do something necessary?

Why Google Experience phones are pretty awesome

As Android has grown, devices fall into one of two major classifications. Some devices are so-called "Google Experience" devices (featuring the phrase "with Google" somewhere on the device). Other devices are, well, not Google Experience devices. What is the difference? I've had a hard time figuring it out.

I think that Google Experience phones are updated by Google itself, while the rest of the devices are supported by the phone's manufacturer. I have an original G1 (a Google Experience phone), and I've gotten prompt updates as each new Android OS version has been released. This is similar to the experience that iPhone users enjoy.

Some devices, such as the HTC Hero and the Motorola Cliq (and the HTC Magic in certain regions), are not Google Experience phones. These phones were released with heavily customized software (such as HTC's Sense UI or Motorola's Motoblur). These customizations, while attractive to some users, also make it much harder for the phone manufacturer to update to a new version of the base Android OS. Both the Hero and the Cliq shipped with Android 1.5, and I don't believe that there are announced plans to update either to 1.6 (or 2.0, for that matter).

At first, I thought that the notion of a Google Experience phone was silly. At the time, the Magic was launching on Rogers with Exchange support, and that somehow disqualified the phone as being a Google Experience device. I now understand that Google Experience really means "unforked code base". In order to add Exchange support, I suspect that HTC had to fork and modify the standard Mail app. While they were able to add a feature that people wanted, it really just makes these phones into some sort of mutant Android device. No thank you. Google should really make it clear to users that the Google Experience is a feature in and of itself.

Android, at this point, is a rapidly evolving platform. Google Experience phones seem to be the best way to keep up with this evolution. I was pleased when I heard a Verizon rep say that the Droid will be a Google Experience phone. Now they just need to release a T-Mobile US GSM version, and I'll be happy. Over time, Android evolution will slow down, and then it might make sense for a manufacturer to fork the Android code base. Maybe they would even be willing to contribute back to the core distribution. But, until then, I'm sticking with Google Experience devices.

Fixing hard disk clicking / aggressive head parking on Mac OS X

I recently bought a Western Digital Scorpio notebook hard drive to put into my 2007-vintage Macbook Pro. Everything seemed fine at first. However, as I used my laptop, I noticed that it would frequently make a quiet clicking noise. At first, I thought that I had gotten a bad disk. However, after doing a little research, it became clear that this is a common problem. This clicking is a "normal" operational noise - it is the sound of the heads parking.

People say that you should just get used to the noise. However, this blog post makes the argument that every one of these clicks is killing your hard disk. Some people claim that this is related to the sudden motion sensor that's built into most (if not all) Apple portables. However, this is a red herring. The disk still clicks even if it is sitting on a table. It is the hard disk's own built-in power management that is causing the head parking. The disk's SMART statistics record the number of head parking cycles. If you want to see this for yourself, you can use either this menu extra or this command line tool (MacPorts). You are looking for the Load Cycle Count value.

To explain the problem (as I understand it), modern hard disks have some responsibility to manage their power consumption. One manifestation of this is to spin down the platters and to park the read/write heads. The operating system can influence the time before the heads are parked by setting the "APM Level" of the drive to a value between 0x00 and 0xfe. Each drive manufacturer is free to interpret this value as they see fit. Mac OS X seems to set a default APM Level for all disks, and I think this value is 0x80. This is fine with Apple-shipped disks, but not necessarily for third party disks.

But wait! Perhaps you have bought the same kind of drive that Apple ships in their laptops. Are you safe? Not necessarily. Allegedly, Apple flashes their own firmware onto the the hard disks that they install at the factory. That's right, you're not running stock disk firmware. My suspicion is that this firmware changes the drive's interpretation of the default APM level. Recently, there was a firmware update from Apple that fixed this problem on disks that were shipped by Apple. Unfortunately, you can't use this utility to flash the new firmware onto a non-Apple drive.

Right, so the two solutions that I see are either:

1. Write our own firmware
2. Set a different APM Level value

Obviously, option 2 looks much more attractive. Bryce McKinlay wrote a utility called hdapm for doing just that. He even includes a launchd configuration to run hdapm as the system starts. One thing not mentioned in the readme is that you need to get the permissions of the launchd config file correct. The file needs to be owned by root (preferably root:wheel), and must not be group- or world-writeable. I also changed the config file a little; here is my version:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
 <key>Label</key>
 <string>hdapm</string>
 <key>ProgramArguments</key>
 <array>
  <string>/usr/local/bin/hdapm</string>
  <string>disk0</string>
  <string>max</string>
 </array>
 <key>RunAtLoad</key>
 <true/>
</dict>
</plist>

The biggest change is that I removed the "LaunchOnlyOnce" and "ServiceDescription" keys. I didn't see a reason to load it only once, and ServiceDescription seemed undocumented. This solution isn't perfect, however. First of all, hdapm uses a seemingly undocumented back door to adjust the APM setting. Ideally, we would actually spawn a daemon that continuously monitors and adjusts the drive's APM level. I'm not yet convinced that Mac OS X won't override my setting. Still, I have been running with this configuration for a couple of days, and things seem to be working well.

I have an open support issue with Western Digital to see if they have a fix for this issue. If there were some way that we could change the way the disk behaves under OSX, we could forego the additional software, which would be great. I've also heard of a utility called wdidle, which allegedly lets you write new idle settings to the hard drive. However, I was unable to find any official site for this software, so I'm not using it.

Finally, I would like to thank two people. First, Doug Aghassi's post really explained the symptoms that he was experiencing and put me on the right track for solving the problem. Thanks, Doug. Also, Bryce McKinlay was kind enough not only to write the hdapm utility, but also to answer the questions that I emailed to him. Thanks, Bryce.

More Painting Space Marines

I have an update to my Space Marine painting. I've continued to shade the marines. After the previous coat of 1:1 Regal Blue to Ultramarine Blue, I added the following:

• 1:2 Regal Blue to Ultramarine Blue
• Ultramarine Blue
• 2:1 Ultramarine Blue to Codex Grey

Each coat is painted in a slightly smaller area. The goal is to shade the model to match an imaginary light source. In my case, my light source is directly above the model. Here are the results:

I'm now only painting 2 marines. I'm going to finish them before starting others, so that I can improve on my technique for those later models.

I also started painting my Tyranid spores. This has been basecoated with Chaos Black spray, then painted with Blood Red, then washed with Chestnut Ink. I had tried Red Ink, but unfortunately, that color is too close to Blood Red.

Painting Space Marines

For some reason, I got an itch to paint some Warhammer 40k figures. I've been slowly assembling them over... I don't know, maybe 2 years. Hey, I have a lot of things that I do in my free time. Anyway, I finally got around to priming them the other day, and I've been painting like a crazy person since then.

Now, I should mention that these aren't the first figures I've painted. I had painted a squad of 5 marines that came in a box along with 6 paints and a brush. Here's one of them.

That was a good learning experience. This time, I have quality glue, basing material, spray primer, a variety of brushes, and lots of paints and inks. I'm posting some photos of various steps of the process. Hopefully, by putting them here, I will actually finish painting them.

---

This space marine has been assembled, based, and primed. The basing material is sand and rock, glued into place with regular white glue. The whole model is sprayed with a flat black primer, to help the other paint stick better.

This marine has had his armor painted with Ultramarine Blue. Actually, his feet are missing some paint, but I'll get around to that. Additionally, the black ground cover has been drybrushed to look like sand and rocks. I started with rocky sand, painted it black, then painted it to look like rocky sand again. Crazy? Probably.

This marine has been washed with a blue ink (which I think has been replaced with Asurmen Blue Wash). Ink is used because it settles in the crevasses and provides great depth.

This marine has had his armor panels painted with a 50/50 mix of Regal Blue and Ultramarine Blue. By leaving a slight gap around the edges, the blue wash peeks through the armor panels, and this looks great.

For those who don't know much about 40k, these figures are pretty small. Here's a comparison shot.

Now imagine trying to paint those eye lenses. Yeah, I'm not looking forward to it, either. Besides the eyes, I still have a lot to do. I plan to put another few layers of blue on the armor, paint the shoulder pad edges, drybrush the metal pieces, and so on. If anybody reads this and has feedback or suggestions, I'd love to hear from you!

I wish Blogger would let me rename tags

Occasionally, if you read this via RSS, you will notice that I repost old articles. This isn't intentional - any time I edit or retag a post in Blogger, it puts it back on the feed. I don't see any way to say "quietly republish this post". The same problem occurs if I want to rename a tag - I have to remove the tag from all posts, and then re-add it to all posts. Please, Google, add features to Blogger to make this less painful.

T-Mobile Visual Voicemail Problems

T-Mobile recently released their Visual Voicemail application in the Android market. It had some launch problems, but those are mostly smoothed out at this point. The app works pretty well, and I'm glad that they have finally implemented it. However, the app does have its share of first-release problems. They are listed here, in the order that I hope T-Mobile addresses them.

VVM doesn't work with Wifi. Most people probably have Wifi enabled on their phones. After all, it's the most efficient (both bytes / time and power / byte) way to tranfer data. However, VVM doesn't work with Wifi. It will neither notify you of new voicemails, nor will it download new messages. In order to make it work, you need to

1. Turn off Wifi
2. Wait or click "Synchronize Voicemails"
3. Turn Wifi back on

Call me crazy, but that's just stupid. At the very least, the "Synchronize Voicemails" button should do those steps for you, similar to the My Account app. There has been some FUD about the reason for this omission. Some people claim that it's for "security". I'm going to make this perfectly clear: there is no security-related reason to prevent people from getting their voicemails over Wifi. It's easy to encrypt data that is transmitted over the internet. There are a number of possible reasons they don't support Wifi. It might just be too much work. Maybe they haven't had time yet. It might be cost prohibitive. Perhaps there is a technical restriction - they would need to read the SIM's IMSI into the app, which Android might not allow. Whatever the case, it's not a security issue.

VVM has a separate notification icon. Every time you get a new voicemail, you get the standard voicemail icon. In addition, you get a new VVM icon. For now, this is fine. If I have Wifi enabled, I still get notified of a new voicemail (via the standard voicemail icon). When the Wifi issue is fixed, however, I would like to see the new icon go away. The notification bar is crowded enough.

VMM uses the wrong audio stream. VVM uses the "media" audio stream. Many people complain that prevents you from using a bluetooth headset to listen to your VM. I don't have a bluetooth headset, so I can't confirm this. It should use the "phone" audio stream.

The UI needs polish. There are some small look-and-feel issues:

1. The VVM status bar icon doesn't match the Android UI Guidelines.
2. After pressing the "Synchronize Voicemails" button, there is no feedback. No spinner, no progress bar, nothing.
3. The long-press context menu on a VM does not include a "delete" option (only Open, Reply As, and Copy To)
4. The buttons that appear when you press the "Menu" button have no icons.
5. The "Copy to" screen is a little too technical. The file name defaults to vmn (i.e. vm0, vm1, vm2). It should instead default to something like "Voicemail from John Smith on 22 Jul, 2009". In addition, the save directory defaults to "/sdcard". Should users really be exposed to UNIX pathnames? Clicking the Save in Directory dropdown presents me with a file browser for my SD card. For me, this lists locations like ".Trashes" (I use a Mac), espeak-data (the data files for the Text-To-Speech engine), "where" (the data for Where), and other places that I probably shouldn't be saving random files. Do I really need to be able to specify the location to save the voicemail? Why not just save everything to /sdcard/voicemails? Or at least, why not assume that all voicemails get saved to /sdcard/voicemails or a subdirectory (i.e. you can't save a voicemail outside this directory, only inside)?

Initial, first-run experience is lousy. When I first installed and ran the app, it wasn't able to connect to the server. After disabling Wifi, it worked. I was taken to a set-up screen, but then got distracted by something and hit the back button. When I relaunched the application, the set-up screen wasn't presented. This worried me (is there some setup that needed to occur), so I uninstalled the app and re-installed it. I don't think I did any harm, but the app didn't behave as I expected, so I didn't know what to think.

Deleting doesn't always work. I'm going to chalk this up to glitch behavior. The first time I used the app, I went through and deleted some old messages. Then I went into the analog voicemail system, and they were back! I deleted them a second time, and now they're really gone. shrug

Now, I don't mind all of those problems. I'm glad that T-Mobile finally released a VVM app. I'm glad that they released it early, warts and all. I hope that they are not done working on it. For me, the Wifi issue is huge. I'm connected to Wifi 90% of the time, and that means that the VVM app doesn't function as a voicemail app 90% of the time. I suspect many other people are in the same boat as me. Furthermore, Google Voice is coming. If the Wifi issue isn't fixed by the time GV is generally available, I might just jump ship, and T-Mobile doesn't want me to do that. I understand if T-Mobile can't fix this on their own - they might need support from Google. Still, every carrier is going to want to provide VVM, and it would behoove Google to provide whatever support necessary.

Getting Started with Stack Overflow

I joined Stack Overflow shortly after it launched, but I didn't do anything with it. I found it in search results here and there, but I never asked any questions. I would have done more, but new users are pretty helpless. You can't vote up or down, you can't comment on answers, you can't post an answer with more than 1 link, etc. It's almost like you're not wanted. Compared to the relative freedom of Wikipedia, it was really demoralizing to me.

I decided tonight to actually try to get some reputation. Most of the interesting stuff happens around 50 reputation, so that's my goal. I answered 2 questions this evening. Suddenly, my rep is skyrocketing. I'm at 31 right now, and I bet that will continue to climb on its own. It seems that people are very willing to vote your answers up if they are relevant. As you can see, it shouldn't be hard to get to the point of actually being able to contribute.

So, if you want to get started with Stack Overflow, here are my suggestions.

1. Go to the newest questions page.
2. Find something that you know something about. Don't troll, and don't post to random topics about which you know nothing.
3. Write an answer.

That should just about do it. Don't despair, it's easier than it initially seems.

Fixing the Xbox 360 's Grinding Noise / Tray Ejection Problem

I spent an evening performing unexpected surgery on my Xbox 360. When I put a game in, the drive made the most horrible grinding noise. On top of that, the drive would not stay closed. The tray would almost always eject seconds after being closed. Research led me to conclude that the rare earth magnet that is part of the disc clamp had probably become unglued. Since my initial warranty has long since expired and the red ring of death warranty only has another year, I decided to crack the case myself.

It's not worth going through the details, but I did find two useful videos. The first is an overview of the problem. The second is a good tutorial on opening the 360's case. I used some Zap-A-Gap brand contact adhesive that I had laying around to actually reattach the magnet.

I felt quite proud to have diagnosed, researched, and fixed the problem on my own (without sending my console to Microsoft for repairs). $100 plus shipping just to have some intern apply some glue is a little extreme. So many people have had this problem that YouTube videos just refer to it as "the grinding noise problem." Either Hitachi (the drive manufacturer) just made a lousy drive, or Microsoft didn't correctly anticipate the effect that their game furnace would have on the glue that Hitachi used. I don't know who is to blame, but Microsoft should extend their warranty on the 360 to 3 years for all defects, not just those that cause the red LEDs to light up in a circular fashion. I don't expect my car to wear out in 2 years, and I use it every day. My game console shouldn't wear out, either.