fix(healthcheck) retry locking protected fn

When ngx.sleep API is not available (e.g. in the log phase) it's not possible to
lock using lua-resty-lock and functions that must run protected were failing.

This change adds a retry method that starts a new light thread that has access
to ngx.sleep and will succeed to lock.

Fix Kong/kong#5137

lib/resty/healthcheck.lua

@@ -416,17 +416,13 @@ end
 ------------------------------------------------------------------------------
 
 
--- Run the given function holding a lock on the target.
--- WARNING: the callback will run unprotected, so it should never
--- throw an error, but always return `nil + error` instead.
--- @param self The checker object
--- @param ip Target IP
--- @param port Target port
--- @param hostname Target hostname
--- @param fn The function to execute
--- @return The results of the function; or nil and an error message
--- in case it fails locking.
-local function locking_target(self, ip, port, hostname, fn)
+--- Helper function to actually run the function holding a lock on the target.
+-- @see locking_target
+local function run_mutexed_fn(premature, self, ip, port, hostname, fn)
+  if premature then
+    return
+  end
+
   local lock, lock_err = resty_lock:new(self.shm_name, {
                   exptime = 10,  -- timeout after which lock is released anyway
                   timeout = 5,   -- max wait time to acquire lock
@@ -436,20 +432,47 @@ local function locking_target(self, ip, port, hostname, fn)
   end
   local lock_key = key_for(self.TARGET_LOCK, ip, port, hostname)
 
-  local ok, err = lock:lock(lock_key)
-  if not ok then
-    return nil, "failed to acquire lock: " .. err
+  local pok, perr = pcall(resty_lock.lock, lock, lock_key)
+  if not pok then
+    self:log(DEBUG, "failed to acquire lock: ", perr)
+    return nil, "failed to acquire lock"
   end
 
   local final_ok, final_err = fn()
 
-  ok, err = lock:unlock()
+  local ok, err = lock:unlock()
   if not ok then
     -- recoverable: not returning this error, only logging it
     self:log(ERR, "failed to release lock '", lock_key, "': ", err)
   end
 
   return final_ok, final_err
+
+end
+
+
+-- Run the given function holding a lock on the target.
+-- WARNING: the callback will run unprotected, so it should never
+-- throw an error, but always return `nil + error` instead.
+-- @param self The checker object
+-- @param ip Target IP
+-- @param port Target port
+-- @param hostname Target hostname
+-- @param fn The function to execute
+-- @return The results of the function; or true in case it fails locking and
+-- will retry asynchronously; or nil+err in case it fails to retry.
+local function locking_target(self, ip, port, hostname, fn)
+  local ok, err = run_mutexed_fn(false, self, ip, port, hostname, fn)
+  if err == "failed to acquire lock" then
+    local _, terr = ngx.timer.at(0, run_mutexed_fn, self, ip, port, hostname, fn)
+    if terr ~= nil then
+      return nil, terr
+    end
+
+    return true
+  end
+
+  return ok, err
 end
 
 

t/06-report_http_status.t

@@ -3,7 +3,7 @@ use Cwd qw(cwd);
 
 workers(1);
 
-plan tests => repeat_each() * 50;
+plan tests => repeat_each() * 53;
 
 my $pwd = cwd();
 
@@ -444,3 +444,50 @@ checking unhealthy targets: nothing to do
 --- no_error_log
 unhealthy HTTP increment
 event: target status '(127.0.0.1:2119)' from 'true' to 'false'
+
+
+=== TEST 5: report_http_status() must work in log phase
+--- http_config eval
+qq{
+    $::HttpConfig
+}
+--- config
+    location = /t {
+        content_by_lua_block {
+            ngx.say("OK")
+        }
+        log_by_lua_block {
+            local we = require "resty.worker.events"
+            assert(we.configure{ shm = "my_worker_events", interval = 0.1 })
+            local healthcheck = require("resty.healthcheck")
+            local checker = healthcheck.new({
+                name = "testing",
+                shm_name = "test_shm",
+                type = "http",
+                checks = {
+                    passive = {
+                        healthy  = {
+                            successes = 3,
+                        },
+                        unhealthy  = {
+                            tcp_failures = 2,
+                            http_failures = 3,
+                        }
+                    }
+                }
+            })
+            local ok, err = checker:add_target("127.0.0.1", 2119, nil, true)
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+            checker:report_http_status("127.0.0.1", 2119, nil, 500, "passive")
+        }
+    }
+--- request
+GET /t
+--- response_body
+OK
+--- no_error_log
+failed to acquire lock: API disabled in the context of log_by_lua