STEPS TO REPRODUCE: 1) Put the following in ~/test.js: "startProfiling(); stopProfiling();" 2) Start shark and put it in programmatic control mode 3) Set shark's sampling interval to 5s 4) Build an optimized js shell with --enable-shark 5) Run |js ~/test.js| ACTUAL RESULTS: Shark gives an alert that says "No samples taken. [CHUDDataSource]" and the js shell hangs. Attaching to the process in gdb doesn't work (gdb itself hangs if I try that). Quitting shark unhangs the shell. EXPECTED RESULTS: Get the alert, but the shell finishes execution. ADDITIONAL INFORMATION: The hang actually happens as the shell process is trying to exit. When it does this, ps shows its state as "UE", which means it's in an uninterruptible wait while trying to exit.
Shark builds were removed in http://hg.mozilla.org/mozilla-central/rev/926651591417 (bug 1150312)