はてなブックマーク

[ 2015-December-27 14:42 ] TL;DR: The Java NIO API caches a maximum-sized direct ByteBuffer for each thread, which looks like a native memory leak if you read or write large blocks from many threads. You can easily patch the JDK yourself to work around this problem. Always use direct ByteBuffers with Java NIO APIs for the best performance, and to avoid this "leak." Under the covers, heap ByteBuffe

The Four Month Bug: JVM statistics cause garbage collection pauses about | archive [ 2015-March-24 16:56 ] TL;DR: The JVM by default exports statistics by mmap-ing a file in /tmp (hsperfdata). On Linux, modifying a memory mapped file can block until disk I/O completes, which can be hundreds of milliseconds. Since the JVM modifies these statistics during garbage collection and safepoints, this caus

[ 2010-September-03 10:04 ] I have been testing one of Intel's "consumer" SSD (X25-M G2) to see if it stores data durably, meaning that if the disk claims the data has been written, it actually survives a power failure. This is important because you want your airline ticket to stay purchased after your buy it, even if the system crashes. The conclusion is that this SSD can lose data in power failu

[ 2009-April-15 13:57 ] I find distributed consensus algorithms, such as Viewstamped Replication or Paxos, to be somewhat magical. Given a set of processes communicating over a network, they will either all eventually agree on the same value, or they will fail to reach agreement if the network is failing in arbitrary ways. These algorithms are used to build reliable distributed systems using repli

[ 2009-February-11 21:36 ] The C standard library function rand is not recommended to be used because older implementations were not very random. The newer function random is typically a better choice, particularly since you can call setstate to give it a large state array, which helps to generate better random numbers. However, neither of these are guaranteed to be thread-safe. That is, if you ca

Figure 1: Linux System Process List Threads Inter-process communication is simple and easy to use when it is used occasionally. However, if there are many processes and many resources to be shared between them, the model quickly becomes cumbersome. Threads were created to make this sort of resource sharing simple and efficient. The concept is that a single process can have a number of threads, and

[ 2005-October-01 20:15 ] Tim Bray describes why Unicode and UTF-8 are wonderful much better than I could, so go read that for an overview of what Unicode is, and why all your programs should support it. What I'm going to tell you is how to use Unicode, and specifically UTF-8, with one of the coolest programming languages, Python, but I have also written an introduction to Using Unicode in C/C++.