Fix deadlock in standalone mcrouter on invalid config #455
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After 6c2142a, standalone mcrouter now deadlocks if router the configuration was incorrect. Spotted on facebook#449, where `test_unknown_named_handles` started failing due to the mcrouter process being tested never existing. GDB [indicates](https://gist.github.com/mszabo-wikia/47916c5655deffdb95332e972a52caf8) a deadlock between three threads: ``` (gdb) info threads Id Target Id Frame * 1 Thread 0x7f7b4cce1e00 (LWP 211878) "mcrouter" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38 2 Thread 0x7f7b43fff6c0 (LWP 211882) "mcr-cpuaux-0" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38 3 Thread 0x7f7b49e0a6c0 (LWP 211879) "IOThreadPool0" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38 ``` Thread 1, the main thread, has triggered exit() and is waiting on the auxiliary thread pool to be destroyed. Thread 2, an auxiliary thread pool thread, is in the process of destroying the CarbonRouterInstance due to 6c2142a and is blocked on destroying the virtual EVBs by child proxies. These however are ultimately sourced from the IO thread pool which is also used by AsyncMcServer. Thread 3, an IO thread pool thread, is blocked by AsyncMcServer which is waiting to be started by later initialization code that never runs due to the config error, preventing the IO thread pool itself from being destroyed. Fix it by initializing the AsyncMcServer only after the router has been initialized.
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Formatting should hopefully be fixed in the latest commit (using https://github.com/facebook/folly/blob/abf77ba9340d7fb225c0a0fe6b355ca2a5652231/folly/.clang-format as a baseline) |
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After 6c2142a, standalone mcrouter now deadlocks if the router configuration was incorrect. Spotted on #449, where
test_unknown_named_handlesstarted failing due to the mcrouter process being tested never exiting.GDB indicates a deadlock between three threads:
6c2142a and is blocked on destroying the virtual EVBs by child proxies. These however are ultimately sourced from the IO thread pool which is also used by AsyncMcServer.
Fix it by initializing the AsyncMcServer only after the router has been initialized.