feat(queue): implement functions Quque.is_full & Queue.can_enqueue (

#13164)

* feat(queue): implement functions `Quque.is_full` & `Queue.will_full`

Generating entries is expensive in some cases,
so we'd better have a way to observe the state of the Queue.

Co-authored-by: Hans Hübner <hans.huebner@gmail.com>
Co-authored-by: Chrono <chrono_cpp@me.com>

kong/tools/queue.lua

@@ -95,16 +95,106 @@ local Queue_mt = {
 }
 
 
-local function make_queue_key(name)
+local function _make_queue_key(name)
   return (workspaces.get_workspace_id() or "") .. "." .. name
 end
 
 
+local function _remaining_capacity(self)
+  local remaining_entries = self.max_entries - self:count()
+  local max_bytes = self.max_bytes
+
+  -- we enqueue entries one by one,
+  -- so it is impossible to have a negative value
+  assert(remaining_entries >= 0, "queue should not be over capacity")
+
+  if not max_bytes then
+    return remaining_entries
+  end
+
+  local remaining_bytes = max_bytes - self.bytes_queued
+
+  -- we check remaining_bytes before enqueueing an entry,
+  -- so it is impossible to have a negative value
+  assert(remaining_bytes >= 0, "queue should not be over capacity")
+
+  return remaining_entries, remaining_bytes
+end
+
+
+local function _is_reaching_max_entries(self)
+  -- `()` is used to get the first return value only
+  return (_remaining_capacity(self)) == 0
+end
+
+
+local function _will_exceed_max_entries(self)
+   -- `()` is used to get the first return value only
+  return (_remaining_capacity(self)) - 1 < 0
+end
+
+
+local function _is_entry_too_large(self, entry)
+  local max_bytes = self.max_bytes
+
+  if not max_bytes then
+    return false
+  end
+
+  if type(entry) ~= "string" then
+    -- handle non-string entry, including `nil`
+    return false
+  end
+
+  return #entry > max_bytes
+end
+
+
+local function _is_reaching_max_bytes(self)
+  if not self.max_bytes then
+    return false
+  end
+
+  local _, remaining_bytes = _remaining_capacity(self)
+  return remaining_bytes == 0
+end
+
+
+local function _will_exceed_max_bytes(self, entry)
+  if not self.max_bytes then
+    return false
+  end
+
+  if type(entry) ~= "string" then
+    -- handle non-string entry, including `nil`
+    return false
+  end
+
+  local _, remaining_bytes = _remaining_capacity(self)
+  return #entry > remaining_bytes
+end
+
+
+local function _is_full(self)
+  return _is_reaching_max_entries(self) or _is_reaching_max_bytes(self)
+end
+
+
+local function _can_enqueue(self, entry)
+  return not (
+    _is_full(self)                       or
+    _is_entry_too_large(self, entry)     or
+    _will_exceed_max_entries(self)       or
+    _will_exceed_max_bytes(self, entry)
+  )
+end
+
+
 local queues = {}
 
 
 function Queue.exists(name)
-  return queues[make_queue_key(name)] and true or false
+  return queues[_make_queue_key(name)] and true or false
 end
 
 -------------------------------------------------------------------------------
@@ -115,7 +205,7 @@ end
 local function get_or_create_queue(queue_conf, handler, handler_conf)
 
   local name = assert(queue_conf.name)
-  local key = make_queue_key(name)
+  local key = _make_queue_key(name)
 
   local queue = queues[key]
   if queue then
@@ -193,6 +283,28 @@ function Queue:count()
 end
 
 
+function Queue.is_full(queue_conf)
+  local queue = queues[_make_queue_key(queue_conf.name)]
+  if not queue then
+    -- treat non-existing queues as not full as they will be created on demand
+    return false
+  end
+
+  return _is_full(queue)
+end
+
+
+function Queue.can_enqueue(queue_conf, entry)
+  local queue = queues[_make_queue_key(queue_conf.name)]
+  if not queue then
+    -- treat non-existing queues as not full as they will be created on demand
+    return false
+  end
+
+  return _can_enqueue(queue, entry)
+end
+
+
 -- Delete the frontmost entry from the queue and adjust the current utilization variables.
 function Queue:delete_frontmost_entry()
   if self.max_bytes then
@@ -260,9 +372,9 @@ function Queue:process_once()
   for _ = 1, entry_count do
     self:delete_frontmost_entry()
   end
-  if self.queue_full then
+  if self.already_dropped_entries then
     self:log_info('queue resumed processing')
-    self.queue_full = false
+    self.already_dropped_entries = false
   end
 
   local start_time = now()
@@ -393,38 +505,54 @@ local function enqueue(self, entry)
     self.warned = nil
   end
 
-  if self:count() == self.max_entries then
-    if not self.queue_full then
-      self.queue_full = true
-      self:log_err("queue full, dropping old entries until processing is successful again")
-    end
+  if _is_reaching_max_entries(self) then
+    self:log_err("queue full, dropping old entries until processing is successful again")
     self:drop_oldest_entry()
+    self.already_dropped_entries = true
   end
 
+  if _is_entry_too_large(self, entry) then
+    local err_msg = string.format(
+      "string to be queued is longer (%d bytes) than the queue's max_bytes (%d bytes)",
+      #entry,
+      self.max_bytes
+    )
+    self:log_err(err_msg)
+
+    return nil, err_msg
+  end
+
+  if _will_exceed_max_bytes(self, entry) then
+    local dropped = 0
+
+    repeat
+      self:drop_oldest_entry()
+      dropped = dropped + 1
+      self.already_dropped_entries = true
+    until not _will_exceed_max_bytes(self, entry)
+
+    self:log_err("byte capacity exceeded, %d queue entries were dropped", dropped)
+  end
+
+  -- safety guard
+  -- The queue should not be full if we are running into this situation.
+  -- Since the dropping logic is complicated,
+  -- further maintenancers might introduce bugs,
+  -- so I added this assertion to detect this kind of bug early.
+  -- It's better to crash early than leak memory
+  -- as analyze memory leak is hard.
+  assert(
+    -- assert that enough space is available on the queue now
+    _can_enqueue(self, entry),
+    "queue should not be full after dropping entries"
+  )
+
   if self.max_bytes then
     if type(entry) ~= "string" then
       self:log_err("queuing non-string entry to a queue that has queue.max_bytes set, capacity monitoring will not be correct")
-    else
-      if #entry > self.max_bytes then
-        local message = string.format(
-          "string to be queued is longer (%d bytes) than the queue's max_bytes (%d bytes)",
-          #entry, self.max_bytes)
-        self:log_err(message)
-        return nil, message
-      end
-
-      local dropped = 0
-      while self:count() > 0 and (self.bytes_queued + #entry) > self.max_bytes do
-        self:drop_oldest_entry()
-        dropped = dropped + 1
-      end
-      if dropped > 0 then
-        self.queue_full = true
-        self:log_err("byte capacity exceeded, %d queue entries were dropped", dropped)
-      end
-
-      self.bytes_queued = self.bytes_queued + #entry
     end
+
+    self.bytes_queued = self.bytes_queued + #entry
   end
 
   self.entries[self.back] = entry
@@ -442,24 +570,56 @@ function Queue.enqueue(queue_conf, handler, handler_conf, value)
   assert(type(handler) == "function",
     "arg #2 (handler) must be a function")
   assert(handler_conf == nil or type(handler_conf) == "table",
-    "arg #3 (handler_conf) must be a table")
-
+    "arg #3 (handler_conf) must be a table or nil")
   assert(type(queue_conf.name) == "string",
     "arg #1 (queue_conf) must include a name")
 
+  assert(
+    type(queue_conf.max_batch_size) == "number",
+    "arg #1 (queue_conf) max_batch_size must be a number"
+  )
+  assert(
+    type(queue_conf.max_coalescing_delay) == "number",
+    "arg #1 (queue_conf) max_coalescing_delay must be a number"
+  )
+  assert(
+    type(queue_conf.max_entries) == "number",
+    "arg #1 (queue_conf) max_entries must be a number"
+  )
+  assert(
+    type(queue_conf.max_retry_time) == "number",
+    "arg #1 (queue_conf) max_retry_time must be a number"
+  )
+  assert(
+    type(queue_conf.initial_retry_delay) == "number",
+    "arg #1 (queue_conf) initial_retry_delay must be a number"
+  )
+  assert(
+    type(queue_conf.max_retry_delay) == "number",
+    "arg #1 (queue_conf) max_retry_delay must be a number"
+  )
+
+  local max_bytes_type = type(queue_conf.max_bytes)
+  assert(
+    max_bytes_type == "nil" or max_bytes_type == "number",
+    "arg #1 (queue_conf) max_bytes must be a number or nil"
+  )
+
   local queue = get_or_create_queue(queue_conf, handler, handler_conf)
   return enqueue(queue, value)
 end
 
 -- For testing, the _exists() function is provided to allow a test to wait for the
 -- queue to have been completely processed.
 function Queue._exists(name)
-  local queue = queues[make_queue_key(name)]
+  local queue = queues[_make_queue_key(name)]
   return queue and queue:count() > 0
 end
 
 
+-- [[ For testing purposes only
 Queue._CAPACITY_WARNING_THRESHOLD = CAPACITY_WARNING_THRESHOLD
+-- ]]
 
 
 return Queue

spec/01-unit/27-queue_spec.lua

@@ -788,4 +788,80 @@ describe("plugin queue", function()
     assert.match_re(log_messages, 'WARN \\[\\] queue continue-processing: handler could not process entries: .*: hard error')
     assert.match_re(log_messages, 'ERR \\[\\] queue continue-processing: could not send entries, giving up after \\d retries.  1 queue entries were lost')  
   end)
+
+  it("sanity check for function Queue.is_full() & Queue.can_enqueue()", function()
+    local queue_conf = {
+      name = "queue-full-checking-too-many-entries",
+      max_batch_size = 99999, -- avoiding automatically flushing,
+      max_entries = 2,
+      max_bytes = nil, -- avoiding bytes limit
+      max_coalescing_delay = 99999, -- avoiding automatically flushing,
+      max_retry_time = 60,
+      initial_retry_delay = 1,
+      max_retry_delay = 60,
+    }
+
+    local function enqueue(queue_conf, entry)
+      Queue.enqueue(
+        queue_conf,
+        function()
+          return true
+        end,
+        nil,
+        entry
+      )
+    end
+
+    assert.is_false(Queue.is_full(queue_conf))
+    assert.is_false(Queue.can_enqueue(queue_conf, "One"))
+    enqueue(queue_conf, "One")
+    assert.is_false(Queue.is_full(queue_conf))
+
+    assert.is_true(Queue.can_enqueue(queue_conf, "Two"))
+    enqueue(queue_conf, "Two")
+    assert.is_true(Queue.is_full(queue_conf))
+
+    assert.is_false(Queue.can_enqueue(queue_conf, "Three"))
+
+
+    queue_conf = {
+      name = "queue-full-checking-too-many-bytes",
+      max_batch_size = 99999, -- avoiding automatically flushing,
+      max_entries = 99999, -- big enough to avoid entries limit
+      max_bytes = 2,
+      max_coalescing_delay = 99999, -- avoiding automatically flushing,
+      max_retry_time = 60,
+      initial_retry_delay = 1,
+      max_retry_delay = 60,
+    }
+
+    assert.is_false(Queue.is_full(queue_conf))
+    assert.is_false(Queue.can_enqueue(queue_conf, "1"))
+    enqueue(queue_conf, "1")
+    assert.is_false(Queue.is_full(queue_conf))
+
+    assert.is_true(Queue.can_enqueue(queue_conf, "2"))
+    enqueue(queue_conf, "2")
+    assert.is_true(Queue.is_full(queue_conf))
+
+    assert.is_false(Queue.can_enqueue(queue_conf, "3"))
+
+    queue_conf = {
+      name = "queue-full-checking-too-large-entry",
+      max_batch_size = 99999, -- avoiding automatically flushing,
+      max_entries = 99999, -- big enough to avoid entries limit
+      max_bytes = 3,
+      max_coalescing_delay = 99999, -- avoiding automatically flushing,
+      max_retry_time = 60,
+      initial_retry_delay = 1,
+      max_retry_delay = 60,
+    }
+
+    enqueue(queue_conf, "1")
+
+    assert.is_false(Queue.is_full(queue_conf))
+    assert.is_true(Queue.can_enqueue(queue_conf, "1"))
+    assert.is_true(Queue.can_enqueue(queue_conf, "11"))
+    assert.is_false(Queue.can_enqueue(queue_conf, "111"))
+  end)
 end)