doc: update example and manual

Signed-off-by: He Xian <[email protected]>

API.md

@@ -122,6 +122,8 @@ Process a host name request. Specifically:
 - SOCKS5 with host name (a.k.a. "socks5h")
 - Any SOCKS4A
 
+*This callback is called from an asynchronous routine.*
+
 **Params**
 
 - `domain`: full qualified domain name and port, like `"www.example.org:80"`
@@ -155,6 +157,8 @@ Process an IPv4 request. Specifically:
 - SOCKS5 with IPv4 address
 - Any SOCKS4
 
+*This callback is called from an asynchronous routine.*
+
 **Params**
 
 - `addr`: address and port, like `"203.0.113.1:80"`
@@ -180,6 +184,8 @@ Process an IPv6 request. Specifically:
 
 - SOCKS5 with IPv6 address
 
+*This callback is called from an asynchronous routine.*
+
 **Params**
 
 - `addr`: address and port, like `"[2001:DB8::1]:80"`
@@ -203,6 +209,8 @@ end
 
 Periodic timer callback. See [neosocksd.setinterval](#neosocksdsetinterval).
 
+*This callback is NOT called from an asynchronous routine.*
+
 **Params**
 
 - `now`: current timestamp in seconds
@@ -228,6 +236,8 @@ end
 
 Generate custom information to be provided in the API `/stats`. See also [stats](#stats).
 
+*This callback is NOT called from an asynchronous routine.*
+
 **Params**
 
 - `dt`: seconds elapsed since last call

example/ruleset.lua

@@ -165,7 +165,15 @@ function ruleset.stats(dt, q)
     return w:concat("\n")
 end
 
+function ruleset.tick(now)
+    libruleset.tick(now)
+    if stat_requests:get(1) ~= stat_requests:get(2) then
+        collectgarbage("step")
+    end
+end
+
 local function main(...)
+    pcall(collectgarbage, "generational")
     neosocksd.setinterval(60)
     -- inherit undefined fields from libruleset
     return setmetatable(ruleset, {