System.out.println performance

最新推荐文章于 2025-12-03 18:58:29 发布

最新推荐文章于 2025-12-03 18:58:29 发布 · 88 阅读

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本文探讨了使用System.out.println进行日志记录时可能遇到的性能问题，特别是当多线程环境中频繁调用此方法时可能导致系统性能显著下降。文章通过代码分析揭示了其内部同步机制如何成为性能瓶颈，并提供了实验数据说明不同场景下的性能退化情况。

Any system that logs vast amounts of information, needs to think about performance. The activity of logging cannot be a synchronous blocking call that returns only when the message has been logged to a persistence store. Enterprise logging systems usually make use of a message bus to carry messages asynchronously to their target persistence store. Be it a database or a file.

Talking about logging brings us to System.out.println() (Lets call is SOP for short). It is a surprisingly commonly method to “log” messages. SOP is not meant to be used as a logging system, but unfortunately there is no dearth of projects that have these statements scattered around the code base. The adverse effects that this statement can bring on the performance of the system is often not recognized as well as it should be.

Why is SOP a bottleneck for performance ? This is why…

Code excerpt from PrintStream.java:

private void write(String s) { try { synchronized (this) { ensureOpen(); textOut.write(s); textOut.flushBuffer(); charOut.flushBuffer(); if (autoFlush && (s.indexOf('\n') >= 0)) out.flush(); } } catch (InterruptedIOException x) { Thread.currentThread().interrupt(); } catch (IOException x) { trouble = true; } }

All SOP calls on a String result in a corresponding call to the private write(String s) method in PrintStream.java. The synchronized block ensures that every thread has to wait for this call to end before it can proceed. Whats more, the calls to flushBuffer() on the BufferedWriter that is textOut result in the execution of more synchronized blocks. These blocks are expensive to execute.

Here is a chart that shows how performance degrades when a program logs 100,000 messages through various threads. The rate of degradation also depends on the number of characters that are passing through the stream.

System.out.println performance:

The degradation experienced in ‘Web application X / Y’ may vary, but it cannot be discounted. Avoid using SOPs to log messages in your app. Even one or two that are left over can harm performance under the right conditions. Let us also not forget about e.printStackTrace() and other forms of writing to console output that follow the same synchronized pattern.