ThreadLocal使用

多线程

#ThreadLocal使用

##Thread介绍

###1、set方法

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public void set(T value) {
     Thread t = Thread.currentThread();
     ThreadLocalMap map = getMap(t);
     if (map != null)
         map.set(this, value);
     else
         createMap(t, value);
 }

每个线程里面居然都有一个threadlocals变量，是ThreadLocalMap的引用，set方法就是往里面设置值

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private void set(ThreadLocal<?> key, Object value) {
        Entry[] tab = table;  //table
        int len = tab.length; //tab的长度
        int i = key.threadLocalHashCode & (len-1); //当前ThreadLocal hashkode且长度
        for (Entry e = tab[i]; e != null;
             e = tab[i = nextIndex(i, len)]) {
            ThreadLocal<?> k = e.get();  //从table数组中拿到
            if (k == key) {
                e.value = value;      //当前value设置给entry里面的，替换掉原值
                return;
            }
            if (k == null) { //当前entry为空
                replaceStaleEntry(key, value, i); //当前key设置进来
                return;
            }
        }
        tab[i] = new Entry(key, value);//table为空，就直接new一个
        int sz = ++size;
        if (!cleanSomeSlots(i, sz) && sz >= threshold)
            rehash(); //如果长度大于threshold(阈值)，重新hash
    }

  • One possible (and common) use is when you have some object that is not thread-safe, but you want to avoid synchronizing access to that object (I’m looking at you, SimpleDateFormat). Instead, give each thread its own instance of the object.
    For example:
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public class Foo
{
    // SimpleDateFormat is not thread-safe, so give one to each thread
    private static final ThreadLocal<SimpleDateFormat> formatter = new ThreadLocal<SimpleDateFormat>(){
        @Override
        protected SimpleDateFormat initialValue()
        {
            return new SimpleDateFormat("yyyyMMdd HHmm");
        }
    };
    public String formatIt(Date date)
    {
        return formatter.get().format(date);
    }
}
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//added by jude end 手续费  扣平台手续费，用户不扣手续费
            //平台收取用户5%的手续费，先打给平台，然后平台垫付
           //充值手续费
            $chongzhi_fee_rate_plat = Core::$recharge_fee;
            $chongzhi_fee_plat = round($payAmount / (1 + $chongzhi_fee_rate_plat) * $chongzhi_fee_rate_plat, 2);
            if ($chongzhi_fee_plat < 0.01)
                $chongzhi_fee_plat = 0.01;
            $this->FinanceAccount->accountOpByAlias("chongzhi_fee_baofoo", $chongzhi_fee_plat, "user:{$m_id}", "site_baofoo",$remark);
            $this->FinanceAccount->accountOpByAlias("chongzhi_fee_out_baofoo", $payAmount*0.001, "site_baofoo", "site_baofoo_out",$remark);//这里的0.01不能改
            //因为实际不收取手续费，所以还给用户，只是有资金记录
            $this->FinanceAccount->accountOpByAlias("site_activity", $chongzhi_fee_plat, "sitebalance", "user:{$m_id}", Core::$DeductFeePrompt);
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