Many-core concurrent programming offers exciting and compelling advantages. The single-core, single-thread programming model is assumed by imperative programming languages. This model offers sequential consistency as its fundamental characteristic. Because many-core systems use layered cache memory systems, sequential consistency is not guaranteed among threads. Because imperative programming languages allow implicit sharing of data between threads, many misguided idioms and optimizations are possible that erroneously assume sequential consistency. One example of this is the double-checked locking optimization. The pernicious nature of these sorts of bugs is they defy programmers’ natural intuition about how programs behave, they are not statically detectable, and there is no way to reliably test a program to rule out the existence of such bugs. A program may appear to work, but have problems appear years later, fail when ported to a different platform, and such problems may be extremely hard to reproduce and track down. In essence, the correctness of the program relies entirely on the expertise and care of the programmer. This is not an acceptable situation for developers of programs that require high reliability.
The D programming language is an imperative programming language with an innovative type system that prevents implicit sharing and also fosters a complete, integrated pure functional subset. It is possible to statically verify that D programs do not have sequential consistency bugs. The double-checked locking optimization bug is not possible. Type support for shared data and immutable data, as well as pure functions, means that mutating data interactions between threads can occur only under carefully controlled conditions. This dramatically reduces the problem space for concurrency bugs from the whole of the source code to a small subset of it, making it a much more tractable problem.
Walter Bright graduated from Caltech in 1979 with a degree in mechanical engineering. He worked for Boeing for 3 years on the development of the 757 stabilizer trim system. He then switched to writing software, in particular compilers, and has been writing them ever since.
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