Revert "MB-43373: Abort memcached if exception thrown from GlobalTask…

…::run v2"

Now FollyExecutorPool no longer catches exceptions on bg threads (see
MB-44253), we don't want to catch them ourselves in GlobalTask - we
want them to be uncaught and trigger std::terminate with a full
backtrace to where the exception was thrown from.

(Note: This was partially reverted by 8828aa7 ("Revert "MB-43818:
GlobalTask::execute: Log task info if exception thrown"), but the
throw was not removed. This patch completes the revert.

This reverts commit b6ed8d0.

Change-Id: I4b4085ee4b4eae3e397d79ade51cb3fc88f67e87
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/147330
Reviewed-by: James Harrison <james.harrison@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>

engines/ep/src/globaltask.cc

@@ -70,13 +70,8 @@ GlobalTask::~GlobalTask() {
 
 bool GlobalTask::execute() {
     // Invoke run with the engine as the target for alloc/dalloc
-    try {
-        BucketAllocationGuard guard(engine);
-        return run();
-    } catch (...) {
-        // Our terminate handler will print details of the exception.
-        std::terminate();
-    }
+    BucketAllocationGuard guard(engine);
+    return run();
 }
 
 void GlobalTask::snooze(const double secs) {

engines/ep/src/globaltask.h

@@ -254,12 +254,6 @@ class GlobalTask {
      * how long to sleep before it should be scheduled again.
      * If the task is complete (and should never be run again), return false.
      *
-     * This method should not throw any (uncaught) exceptions - if it did then
-     * the task is potentially in a undefined state and hence not possible to
-     * know if it should be re-scheduled or not. If any exceptions are thrown
-     * then the exception will be logged and the program will be terminated
-     * via std::terminate.
-     *
      * @return Whether or not this task should be rescheduled
      */
     virtual bool run() = 0;