原理，在Looper的loop方法中，有统计耗时的逻辑，在此基础上，增加了Thread的堆栈信息打印。
Looper.java
/* If set, the looper will show a warning log if a message dispatch takes longer than time. */ private long mSlowDispatchThresholdMs;
/** {@hide} */ public void setSlowDispatchThresholdMs(long slowDispatchThresholdMs) { mSlowDispatchThresholdMs = slowDispatchThresholdMs; }
/**
- Control logging of messages as they are processed by this Looper. If
- enabled, a log message will be written to printer
- at the beginning and ending of each message dispatch, identifying the
- target Handler and message contents.
- @param printer A Printer object that will receive log messages, or
- null to disable message logging. */ public void setMessageLogging(@Nullable Printer printer) { mLogging = printer; }