Comment 36 for bug 680444

I have run into this issue. Also when using Thunderbird. I thought it was the 14 to 15 Thunderbird upgrade in 12.04 since the problem started basically overnight, and coincidentally after the 14 to 15 Thunderbird upgrade. I was pulling my hair out since Thunderbird was basically unusable -- it would run normally but pause for a few seconds after opening a new message, deleting messages, or just clicking to select messages. It would also pause while writing a new message, so whatever you typed didn't show up right away but instead be displayed all of the sudden a few seconds later. Totally annoying.

Another symptom was Unity dimming the Thunderbird window at some points because it thought that TB was unresponsive (hung), though it would undim it a few seconds later -- I would notice this behavior when TB initially ran and it was establishing the connection to my IMAP server. I would also notice this same behavior at some other times, like opening a new message, though these were rare.

I downgraded to TB 14 and it didn't help. I ran TB without extensions; in safe mode, etc. to no avail. It was completely puzzling because I had not been having this problem before.

Running strace on the Thunderbird executable revealed one of the same symptoms mentioned by people above, i.e. lots of these:

sendmsg(38, {msg_name(0)=NULL, msg_iov(2)=[{"l\4\1\1\24\1\0\0002\304\23\0x\0\0\0\1\1o\0\25\0\0\0/org/a11"..., 136}, {"\5\0\0\0:1.48\0\0\0!\0\0\0/org/a11y/atspi/"..., 276}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 412

Then, somehow I found this bug and confirmed in top that each time I had a pause, both thunderbird and dbus-daemon would be hogging the CPU. I did notice that the dbus-daemon that was hogging the CPU was not the system DBus daemon, but one associated with at-spi2 (accessability).

Fortunately, I don't need accessability features, so I looked for ways to prevent all the at-spi2 stuff from auto-starting upon logging into my Unity session to see if that fixed the problem I was having with Thunderbird. Turns out that in Ubuntu 12.04 you can disable at-spi2 by using gsettings like this:

shell$ gsettings set org.gnome.desktop.interface toolkit-accessibility false

After logging out and logging back in, the at-spi2 processes were not running. I then fired up Thunderbird and the problem was completely gone. In fact, Thunderbird feels now a lot snappier -- everything (opening messages, deleting messages, replying, etc.) seems faster. But, the most important thing is that the annoying pauses/temporary freezes seem to be completely gone.

What is very puzzling is that this problem happened overnight for me. I could have been an unrelated 12.04 package update, but if that is the case, I don't know what package it was. In any case, if you end up reading this bug, and your symptoms are similar to the ones described here then try disabling at-spi2.