###Background

As a terminal junkie, I've started messing around with a combination of mpd (Music Player Daemon) and a player, ncmpcpp (NCurses Media Player Client C++).

I installed these via Homebrew - a simple brew install mpd ncmpcpp. A bit of configuration later, and the apps are running quite nicely. The effect is actually rather impressive:

The problem I run into is when I want to run mpd automatically instead of having it launch in my terminal. It comes with a launchd plist, so I install that, and it appears to work - The problem is that whatever I'm playing, be that an MP3, streaming audio from a server, or whatever, the audio stutters every 5 seconds

This absolutely does not happen when mpd is invoked directly from the command line, only when it's fired off via launchd.

Here's what the plist looks like:

<!--homebrew.mxcl.mpd.plist-->
<?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>KeepAlive</key>
    <true/>
    <key>Label</key>
    <string>homebrew.mxcl.mpd</string>
    <key>ProcessType</key>
    <string>Interactive</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/opt/mpd/bin/mpd</string>
        <string>--no-daemon</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>WorkingDirectory</key>
    <string>/usr/local</string>
</dict>
</plist>

The "ProcessType" interactive was added by me in an attempt to force launchd to give the daemon higher priority, to no effect.

###Things I've already eliminated

• CPU / Disk IO

The system is relatively quiet - during the stutters, mpd is not even on the top 25 for memory or CPU usage, and load is well below 1.0

• Incorrect environment causing bad config settings to be loaded

My mpd config is the one being loaded from ~/.mpdconf - same as it is when I run it by hand.

This appears to be a symptom of the way launchd chooses to handle the process.

###The ultimate question Why is the daemon so misbehaved when run under launchd, but not when run via terminal?

###Bonus question: What about the way launchd kicks off processes could be making this behavior manifest?

###Background

As a terminal junkie, I've started messing around with a combination of mpd (Music Player Daemon) and a player, ncmpcpp (NCurses Media Player Client C++).

I installed these via Homebrew - a simple brew install mpd ncmpcpp. A bit of configuration later, and the apps are running quite nicely. The effect is actually rather impressive:

The problem I run into is when I want to run mpd automatically instead of having it launch in my terminal. It comes with a launchd plist, so I install that, and it appears to work - The problem is that whatever I'm playing, be that an MP3, streaming audio from a server, or whatever, the audio stutters every 5 seconds

This absolutely does not happen when mpd is invoked directly from the command line, only when it's fired off via launchd.

Here's what the plist looks like:

<!--homebrew.mxcl.mpd.plist-->
<?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>KeepAlive</key>
    <true/>
    <key>Label</key>
    <string>homebrew.mxcl.mpd</string>
    <key>ProcessType</key>
    <string>Interactive</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/opt/mpd/bin/mpd</string>
        <string>--no-daemon</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>WorkingDirectory</key>
    <string>/usr/local</string>
</dict>
</plist>

The ProcessType interactive was added by me in an attempt to force launchd to give the daemon higher priority, to no effect.

###Debugging?

If we dtruss the process, there is a huge blast of identical gettimeofday messages correlated with every stutter. It looks like this:

gettimeofday(0x10A03FD40, 0x0, 0x1000)       = 1428698761 0

###Things I've already eliminated

• CPU / Disk IO

The system is relatively quiet - during the stutters, mpd is not even on the top 25 for memory or CPU usage, and load is well below 1.0

• Incorrect environment causing bad config settings to be loaded

My mpd config is the one being loaded from ~/.mpdconf - same as it is when I run it by hand.

This appears to be a symptom of the way launchd chooses to handle the process.

###The ultimate question Why is the daemon so misbehaved when run under launchd, but not when run via terminal?

###Bonus question: What about the way launchd kicks off processes could be making this behavior manifest?