SERVER-30170 Embedded can now shutdown and re-initialize.

- ServiceContext* is now closer to be an instance context for the database. We still don't support multiple instances but I wrote the new code with this in mind. Teardown and reinitialize then becomes a matter of being able to delete and re-create the ServiceContext*.
- Use the new MONGO_INITIALIZER that supports deinit/reinit to be able to re-initialize global systems that are decorations on ServiceContext.
- Move creation/destruction of ServiceContext* out of MONGO_INITIALIZER. This so we can hold an exclusive lock during as much as possible of the shutdown (like how mongod does)
- New ServiceContext registrer where we can link in different implementations of ServiceContext (replaces the SetGlobalEnvironment MONGO_INITIALIZER)
- As a result the SetGlobalEnvironment prerequisite for MONGO_INITIALIZERs is gone.
- The ServiceContext is passed to runGlobalInitializers, put in InitializationContext/DeinitializationContext so the initializers know which context they operate on.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/mongo/executor/connection_pool.cpp b/src/mongo/executor/connection_pool.cpp
index 43d061db5a8..c00fe1c739b 100644
--- a/src/mongo/executor/connection_pool.cpp
+++ b/src/mongo/executor/connection_pool.cpp
@@ -280,7 +280,9 @@ ConnectionPool::ConnectionPool(std::unique_ptr<DependentTypeFactoryInterface> im
 }
 
 ConnectionPool::~ConnectionPool() {
-    if (_manager) {
+    // If we're currently destroying the service context the _manager is already deleted and this
+    // pointer dangles. No need for cleanup in that case.
+    if (hasGlobalServiceContext() && _manager) {
         _manager->remove(this);
     }
 }