关于Synchronized方法使用问题

前言

今天遇到一个问题(项目)，客户测试，插入2张SIM卡重启，只有卡1收到短信。正常情况是收到2条短信，此问题是偶现，概率不高。

代码

关键代码如下，通过for循环每张卡发送短信。

List<SubscriptionInfo> subInfoList = SubscriptionManager.from(                        mContext).getActiveSubscriptionInfoList();                Log.d(TAG, "subInfoList size " + subInfoList.size());                for (SubscriptionInfo subscriptionInfo : subInfoList) {                ....                sendMms(msg, getReturnPhoneNumber(slot_imei, sim_number));}

sendMms方法实现：

    private void sendMms(Message msg, String sendText) {    int subid = msg.getData().getInt(Sms.SUBSCRIPTION_ID);        ...        SmsManager smsManager = SmsManager.getSmsManagerForSubscriptionId(subid);        PendingIntent pendInt = createSendIntent(subid, sendText, tiems);        String encrypt_text = encrypt(sendText);        if (encrypt_text.length() > 70) {            ArrayList<String> parts = smsManager.divideMessage(encrypt_text);            ArrayList<PendingIntent> list = new ArrayList<PendingIntent>();            list.add(pendInt);            smsManager.sendMultipartTextMessage(address, scAddress, parts, list, null);        } else {            smsManager.sendTextMessage(address, scAddress, encrypt_text, pendInt, null);        }    }

日志分析

日志显示

11-16 14:22:07.713052  1649  2745 D LockChangeReceiver: subInfoList size 211-16 14:22:07.734687  1649  2745 D LockChangeReceiver: last_sim iccid:89911100185008968471 current iccid:8991119018513666485211-16 14:22:07.788860  1649  2745 D LockChangeReceiver: subid: 7 address [phone] scAddress: [phone] sendText: *CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:11-16 14:22:07.799236  1649  2745 D LockChangeReceiver: encryptedMsg: cwU4Yp/CTK97F7TnAT39McKzpfNW/qM3fEbCepmUIADsgWN3xOzmeUPXJgzMFO9Z11-16 14:22:07.913115  1649  2745 D LockChangeReceiver: last_sim iccid:8991101505026689073f current iccid:8991119018506030042411-16 14:22:08.004434  1649  2745 D LockChangeReceiver: subid: 3 address [phone] scAddress: [phone] sendText: *CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:11-16 14:22:08.008499  1649  2745 D LockChangeReceiver: encryptedMsg: cwU4Yp/CTK97F7TnAT39McKzpfNW/qM3fEbCepmUIADsgWN3xOzmeUPXJgzMFO9Z

上面的日志显示，sim 卡 subid 3，7都发送了短信出去。

发送结果

11-16 14:22:36.926676  1649  1649 D LockChangeReceiver: action: com.lava.action.resend_msg11-16 14:22:36.926924  1649  1649 W LockChangeReceiver: 11-16 14:22:36.926924  1649  1649 W LockChangeReceiver:  send msg result 3411-16 14:22:36.927063  1649  1649 W LockChangeReceiver: Bundle[{msg_ref_num=34, sub_id=3, pdu_size=77, body=*CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:, send_times=0}]11-16 14:22:36.927194  1649  1649 W LockChangeReceiver: send msg success subid 3 body:*CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:11-16 14:22:37.964181  1649  1649 D LockChangeReceiver: action: com.lava.action.resend_msg11-16 14:22:37.964313  1649  1649 W LockChangeReceiver: 11-16 14:22:37.964313  1649  1649 W LockChangeReceiver:  send msg result 22811-16 14:22:37.964431  1649  1649 W LockChangeReceiver: Bundle[{msg_ref_num=228, sub_id=3, pdu_size=77, body=*CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:, send_times=0}]11-16 14:22:37.964498  1649  1649 W LockChangeReceiver: send msg success subid 3 body:*CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:

从上面的日志可以看出，设备发送了2次短信，但是都是subid = 3的sim卡。所以用户反馈sim卡二未发送短信到服务器平台。

原因分析

1.在方法sendMms里面有一个系统接口调用：

SmsManager smsManager = SmsManager.getSmsManagerForSubscriptionId(subid);

此方法实现：

    /**     * Get the the instance of the SmsManager associated with a particular subscription id     *     * @param subId an SMS subscription id, typically accessed using     *   {@link android.telephony.SubscriptionManager}     * @return the instance of the SmsManager associated with subId     */    public static SmsManager getSmsManagerForSubscriptionId(int subId) {        // TODO(shri): Add javadoc link once SubscriptionManager is made public api        synchronized(sLockObject) {            SmsManager smsManager = sSubInstances.get(subId);            if (smsManager == null) {                smsManager = new SmsManager(subId);                sSubInstances.put(subId, smsManager);            }            return smsManager;        }    }

这里面有同步关键字synchronized。当程序执行到这个地方后，由于时间长，至第一个程序没有执行完，第二个程序也执行到这里，此时第一个程序执行完成，返回结果，第二个程序也得到结果，但是是一个的结果。这样2个程序得到同样的结果对象。最终以相同的SIM卡发送短信。

解决方案

• 在sendMms方法中添加关键字synchronized，避免多程序进入。
• 在for循环中添加延时，每执行一次 暂停N百毫秒