util: create but do not start reloadable fiber

This commit makes the whole vshard use `reloadable_fiber_new` instead of
the `reloadable_fiber_create`, from now on reloadable fiber is not
started, just created. This allows all functions not to yield, when
creating such fibers.

The initial motivation was `log_ratelimit` module, where we cannot yield
during creation of the flush fiber, since otherwise it may happen, that
several logs through limiters from different fibers may create several
flush fibers.

It was decided to apply that strategy everywhere, firstly, for the sake of
consistency and, secondly, in order not to repeat the same error in the
future - using `new` instead of `create` will protect us from creating
duplicate reloadable fibers from different fibers.

Needed for #606

NO_DOC=internal

Author: Serpentian

test/unit/util.result

@@ -34,7 +34,7 @@ function slow_fail() fiber.sleep(0.01) error('Error happened.') end
 fake_M.reloadable_function = function () fake_M.reloadable_function = slow_fail; slow_fail() end
 ---
 ...
-fib = util.reloadable_fiber_create('Worker_name', fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new('Worker_name', fake_M, 'reloadable_function')
 ---
 ...
 -- Check that the fiber starts with the proper name
@@ -62,7 +62,7 @@ log.info(string.rep('a', 1000))
 fake_M.reloadable_function = function () fiber.sleep(0.01); return true end
 ---
 ...
-fib = util.reloadable_fiber_create('Worker_name', fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new('Worker_name', fake_M, 'reloadable_function')
 ---
 ...
 while not test_run:grep_log('default', 'module is reloaded, restarting') do fiber.sleep(0.01) end
@@ -79,7 +79,7 @@ fib:cancel()
 name = string.rep('a', 512)
 ---
 ...
-fib = util.reloadable_fiber_create(name, fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new(name, fake_M, 'reloadable_function')
 ---
 ...
 fib:cancel()

test/unit/util.test.lua

@@ -14,7 +14,7 @@ function slow_fail() fiber.sleep(0.01) error('Error happened.') end
 -- Check autoreload on function change during failure.
 fake_M.reloadable_function = function () fake_M.reloadable_function = slow_fail; slow_fail() end
 
-fib = util.reloadable_fiber_create('Worker_name', fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new('Worker_name', fake_M, 'reloadable_function')
 -- Check that the fiber starts with the proper name
 while not test_run:grep_log('default', 'Worker_name.+reloadable_function has been started') do fiber.sleep(0.01); end
 while not test_run:grep_log('default', 'reloadable function reloadable_function has been changed') do fiber.sleep(0.01); end
@@ -25,14 +25,14 @@ log.info(string.rep('a', 1000))
 
 -- Check reload feature.
 fake_M.reloadable_function = function () fiber.sleep(0.01); return true end
-fib = util.reloadable_fiber_create('Worker_name', fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new('Worker_name', fake_M, 'reloadable_function')
 while not test_run:grep_log('default', 'module is reloaded, restarting') do fiber.sleep(0.01) end
 test_run:grep_log('default', 'reloadable_function has been started', 1000)
 fib:cancel()
 
 -- Re-loadable fiber must truncate too long name.
 name = string.rep('a', 512)
-fib = util.reloadable_fiber_create(name, fake_M, 'reloadable_function')
+fib = util.reloadable_fiber_new(name, fake_M, 'reloadable_function')
 fib:cancel()
 
 -- Yielding table minus.

vshard/log_ratelimit.lua

@@ -173,7 +173,7 @@ local function ratelimit_create(cfg)
     setmetatable(ratelimit, ratelimit_mt)
     M.limiters[ratelimit.name] = ratelimit
     if M.flush_fiber == nil then
-        M.flush_fiber = util.reloadable_fiber_create(
+        M.flush_fiber = util.reloadable_fiber_new(
             'vshard.ratelimit_flush', M, 'ratelimit_flush_f')
     end
     return ratelimit

vshard/router/init.lua

@@ -457,7 +457,7 @@ local function discovery_set(router, new_mode)
         -- is found. But it is the case already. So nothing to do.
         return
     end
-    router.discovery_fiber = util.reloadable_fiber_create(
+    router.discovery_fiber = util.reloadable_fiber_new(
         'vshard.discovery.' .. router.name, M, 'discovery_f', router)
 end
 

vshard/storage/init.lua

@@ -3085,9 +3085,8 @@ local function rebalancer_role_update()
     elseif need_rebalancer then
         if not M.rebalancer_fiber then
             log.info('Starting the rebalancer')
-            M.rebalancer_fiber =
-                util.reloadable_fiber_create('vshard.rebalancer', M,
-                                             'rebalancer_f')
+            M.rebalancer_fiber = util.reloadable_fiber_new(
+                'vshard.rebalancer', M, 'rebalancer_f')
             return
         end
     end
@@ -3381,11 +3380,11 @@ local function master_role_update()
     if this_is_master() and M.is_configured then
         if not M.collect_bucket_garbage_fiber then
             M.collect_bucket_garbage_fiber =
-                util.reloadable_fiber_create('vshard.gc', M, 'gc_bucket_f')
+                util.reloadable_fiber_new('vshard.gc', M, 'gc_bucket_f')
         end
         if not M.recovery_fiber then
             M.recovery_fiber =
-                util.reloadable_fiber_create('vshard.recovery', M, 'recovery_f')
+                util.reloadable_fiber_new('vshard.recovery', M, 'recovery_f')
         end
     else
         if M.collect_bucket_garbage_fiber then
@@ -3494,7 +3493,7 @@ end
 local function instance_watch_update()
     if M.this_replicaset.is_master_auto then
         if not M.instance_watch_fiber then
-            M.instance_watch_fiber = util.reloadable_fiber_create(
+            M.instance_watch_fiber = util.reloadable_fiber_new(
                 'vshard.state_watch', M, 'instance_watch_f')
         end
         return

vshard/util.lua

@@ -102,7 +102,7 @@ end
 -- errors and module reload.
 -- This loop executes the latest version of itself in case of
 -- reload of that module.
--- See description of parameters in `reloadable_fiber_create`.
+-- See description of parameters in `reloadable_fiber_new`.
 --
 local function reloadable_fiber_main_loop(module, func_name, data)
     local func = module[func_name]
@@ -135,9 +135,9 @@ local function reloadable_fiber_main_loop(module, func_name, data)
 end
 
 --
--- Create a new fiber which runs a function in a loop. This loop
--- is aware of reload mechanism and it loads a new version of the
--- function in that case.
+-- Create but do not start a new fiber which runs a function in a loop. This
+-- loop is aware of reload mechanism and it loads a new version of the function
+-- in that case.
 -- To handle module reload and run new version of a function
 -- in the module, the function should just return.
 -- @param fiber_name Name of a new fiber. E.g.
@@ -148,12 +148,11 @@ end
 -- @param data Data to be passed to the specified function.
 -- @retval New fiber.
 --
-local function reloadable_fiber_create(fiber_name, module, func_name, data)
+local function reloadable_fiber_new(fiber_name, module, func_name, data)
     assert(type(fiber_name) == 'string')
     local xfiber = fiber.new(reloadable_fiber_main_loop, module, func_name, data)
     xfiber:name(fiber_name, {truncate = true})
     xfiber:wakeup()
-    fiber.yield()
     return xfiber
 end
 
@@ -483,7 +482,7 @@ return {
     core_version = tnt_version,
     uri_eq = uri_eq,
     tuple_extract_key = tuple_extract_key,
-    reloadable_fiber_create = reloadable_fiber_create,
+    reloadable_fiber_new = reloadable_fiber_new,
     future_wait = future_wait,
     generate_self_checker = generate_self_checker,
     async_task = async_task,