本节深入探讨Lua的底层机制、元编程技术、虚拟机原理以及高性能编程技巧,特别针对Android平台进行优化适配。
-- 查看字节码(Lua 5.2+)
local function test(a)
return a * 2 + 1
end
local dump = require("dump")
print(dump.bytecode(test))
-- 自定义代码加载
local chunk = load("return 1+1", "=(debug)", "t", {
__index = _G,
print = function(...)
android.util.Log.d("LUA", table.concat({...}, "\t"))
end
})
底层原理:
-- 控制GC行为
collectgarbage("setpause", 100) -- 控制内存增长
collectgarbage("setstepmul", 200) -- 控制回收速度
-- 弱引用表
local weakValues = setmetatable({}, {__mode = "v"})
local weakKeys = setmetatable({}, {__mode = "k"})
-- 对象生命周期追踪
debug.setmetatable(nil, {
__gc = function(obj)
print("GC回收:", tostring(obj))
end
})
性能要点:
-- 沙箱环境构造
function createSandbox()
local env = {
print = print,
math = math,
_VERSION = _VERSION
}
return setmetatable(env, {
__index = function(_, k)
error("禁止访问:"..tostring(k))
end,
__newindex = function(_, k, v)
error("禁止修改:"..tostring(k))
end
})
end
-- 受限执行
local unsafeCode = "os.execute('rm -rf /')"
local ok, err = pcall(setfenv(loadstring(unsafeCode), createSandbox()))
安全实践:
-- 运行时函数生成
function createAdder(n)
local code = {"return function(x) return x + ", n, " end"}
return load(table.concat(code))()
end
-- 预编译缓存
local cache = {}
function memoizedCompile(code)
if not cache[code] then
cache[code] = load(code)
end
return cache[code]
end
-- JIT优化提示(LuaJIT)
--[[jit.opt.start(3) -- 优化级别
local hotfunc = jit.on(func, true)]]
优化建议:
-- 简单协程池
local coPool = {
pool = {},
get = function(self)
for i, co in ipairs(self.pool) do
if coroutine.status(co) == "suspended" then
table.remove(self.pool, i)
return co
end
end
return coroutine.create(function() end)
end,
recycle = function(self, co)
table.insert(self.pool, co)
end
}
-- 事件驱动调度
local scheduler = {
events = {},
add = function(self, co, ...)
table.insert(self.events, {co=co, args={...}})
end,
run = function(self)
while #self.events > 0 do
local event = table.remove(self.events, 1)
coroutine.resume(event.co, unpack(event.args))
end
end
}
设计模式:
-- 封装Android Handler
local Fiber = {
handler = luajava.newInstance("android.os.Handler")
}
function Fiber:start(fn)
local co = coroutine.create(fn)
self.handler:post(luajava.createProxy("java.lang.Runnable", {
run = function()
local ok, res = coroutine.resume(co)
if not ok then
android.util.Log.e("FIBER", res)
end
end
}))
end
-- 使用示例
Fiber:start(function()
local data = fetchNetworkData() -- 可yield的耗时操作
updateUI(data)
end)
混合调度:
-- 简单性能分析器
local Profiler = {
records = {},
start = function(self, tag)
self.records[tag] = os.clock()
end,
stop = function(self, tag)
local duration = os.clock() - (self.records[tag] or 0)
print(string.format("%s: %.2fms", tag, duration*1000))
end
}
-- 使用Android Trace
local Trace = luajava.bindClass("android.os.Trace")
function traceSection(name)
Trace:beginSection(name)
return {
__gc = function() Trace:endSection() end
}
end
分析工具:
-- 对象复用池
local TablePool = {
pool = setmetatable({}, {__mode = "k"}),
get = function(self)
for t in pairs(self.pool) do
self.pool[t] = nil
return t
end
return {}
end,
recycle = function(self, t)
for k in pairs(t) do t[k] = nil end
self.pool[t] = true
end
}
-- 预分配数组
function createArray(size, init)
local arr = {}
for i = 1, size do
arr[i] = init
end
return arr
end
-- 使用FFI固定内存(LuaJIT)
--[[local ffi = require("ffi")
local buf = ffi.new("int[?]", 1024)]]
优化原则:
-- 高效Java方法调用
local ArrayList = luajava.bindClass("java.util.ArrayList")
local list = ArrayList()
local addMethod = list.getClass():getMethod("add",
{luajava.bindClass("java.lang.Object")})
-- 直接调用避免反射开销
for i = 1, 100 do
addMethod:invoke(list, {tostring(i)})
end
-- 使用JNI数组
local env = luajava.getEnv()
local jarray = env:NewIntArray(10)
env:SetIntArrayRegion(jarray, 0, 10, {1,2,3,4,5})
性能关键:
-- LuaJIT FFI示例
local ffi = require("ffi")
ffi.cdef[[
typedef struct {
int x, y;
} Point;
double sqrt(double x);
]]
-- 调用系统库
local math = ffi.load("m")
print(math.sqrt(2)) -- 1.414
-- 与Android交互
local Point = ffi.metatype("Point", {
__index = {
length = function(self)
return math.sqrt(self.x^2 + self.y^2)
end
}
})
最佳实践:
-- 原子操作模拟
local atomic = {
value = 0,
add = function(self, delta)
local old, new
repeat
old = self.value
new = old + delta
until self:cas(old, new)
return new
end,
cas = function(self, expected, new)
if self.value == expected then
self.value = new
return true
end
return false
end
}
-- 使用Android原子类
local AtomicInteger = luajava.bindClass("java.util.concurrent.atomic.AtomicInteger")
local counter = AtomicInteger(0)
counter:addAndGet(1)
并发原则:
-- Actor模型实现
local Actor = {
queue = {},
running = false,
send = function(self, msg)
table.insert(self.queue, msg)
if not self.running then
self:process()
end
end,
process = function(self)
self.running = true
while #self.queue > 0 do
local msg = table.remove(self.queue, 1)
self:handle(msg)
end
self.running = false
end
}
-- 使用Android的MessageQueue
local HandlerThread = luajava.bindClass("android.os.HandlerThread")
local thread = HandlerThread("Worker")
thread:start()
local handler = luajava.newInstance("android.os.Handler", thread:getLooper())
架构建议: