cache_store: handle missing process.

Library/Homebrew/cache_store.rb

@@ -89,9 +89,15 @@ def db
           end
         rescue ErrorDuringExecution, Timeout::Error
           odebug "Failed to read #{dbm_file_path}!"
-          Process.kill(:KILL, dbm_test_read_cmd.pid)
+          begin
+            Process.kill(:KILL, dbm_test_read_cmd.pid)
+          rescue Errno::ESRCH
+            # Process has already terminated.
+            nil
+          end
           false
         end
+        Utils::Analytics.report_event("dbm_test_read", dbm_test_read_success.to_s)
         cache_path.delete unless dbm_test_read_success
       end
       DBM.open(dbm_file_path, DATABASE_MODE, DBM::WRCREAT)

docs/Analytics.md

@@ -28,7 +28,8 @@ Homebrew's analytics records the following different events:
 - an `event` hit type with the `install` event category and the Homebrew formula from a non-private GitHub tap you install plus any used options, e.g. `wget --with-pcre` as the action and an event label e.g. `macOS 10.12, non-/usr/local, CI` to indicate the OS version, non-standard installation location and invocation as part of CI. This allows us to identify the formulae that need fixing and where more easily.
 - an `event` hit type with the `install_on_request` event category and the Homebrew formula from a non-private GitHub tap you have requested to install (e.g. explicitly named it with a `brew install`) plus options and an event label as above. This allows us to differentiate the formulae that users intend to install from those pulled in as dependencies.
 - an `event` hit type with the `cask_install` event category and the Homebrew cask from a non-private GitHub tap you install as the action and an event label as above. This allows us to identify the casks that need fixing and where more easily.
-- an `event` hit type with the `BuildError` event category and the Homebrew formula that failed to install, e.g. `wget` as the action and an event label e.g. `macOS 10.12`
+- an `event` hit type with the `BuildError` event category and the Homebrew formula that failed to install, e.g. `wget` as the action and an event label e.g. `macOS 10.12`.
+- an `event` hit type with the `dbm_test_read` event category and `true` or `false` as the action (depending on if a corrupt DBM database was detected) and an event label e.g. `macOS 10.12`.
 
 You can also view all the information that is sent by Homebrew's analytics by setting `HOMEBREW_ANALYTICS_DEBUG=1` in your environment. Please note this will also stop any analytics from being sent.