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 2
11-16 14:22:07.734687  1649  2745 D LockChangeReceiver: last_sim iccid:89911100185008968471 current iccid:89911190185136664852
11-16 14:22:07.788860  1649  2745 D LockChangeReceiver: subid: 7 address +917065333399 scAddress: +919811009998 sendText: *CRED* IMEI: 862893009046736 NEW MOBILE NUMBER:
11-16 14:22:07.799236  1649  2745 D LockChangeReceiver: encryptedMsg: cwU4Yp/CTK97F7TnAT39McKzpfNW/qM3fEbCepmUIADsgWN3xOzmeUPXJgzMFO9Z
11-16 14:22:07.913115  1649  2745 D LockChangeReceiver: last_sim iccid:8991101505026689073f current iccid:89911190185060300424
11-16 14:22:08.004434  1649  2745 D LockChangeReceiver: subid: 3 address +917065333399 scAddress: +919811009998 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_msg
11-16 14:22:36.926924  1649  1649 W LockChangeReceiver:
11-16 14:22:36.926924  1649  1649 W LockChangeReceiver:  send msg result 34
11-16 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_msg
11-16 14:22:37.964313  1649  1649 W LockChangeReceiver:
11-16 14:22:37.964313  1649  1649 W LockChangeReceiver:  send msg result 228
11-16 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