What went wrong with the libdispatch (a tale of caution for the future of concurrency).

Back in the mid 2000s processors performance started to plateau and chip makers like Intel told the world that the time of ever increasing the CPU clock speed was not going to be enough. They would not be able to meet Moore's law that way anymore but they had another way: to pack more cores onto the same chip. There was a catch of course, developers would need to update their software if they wanted to be able to take advantage of these many cores. Back then some believed that in 10 years time consumer machines with 80 cores (or even more) would be common. Fast-forward to today's 2020 and most consumer machines have about 4 cores and pro machines have about 8 to 12 cores. Something must have gone wrong along the way. Spoiler: multithreading is hard.

Apple responded in 2008 with the announcement of Mac OS X 10.6 Snow Leopard (considered by some to be the best Mac OS version ever released) which included the libdispatch (a.k.a. Grand Central Dispatch). I was there at WWDC 2008 when it was announced and we were all ecstatic, it was probably the most exciting WWDC I've attended (I would attend 5 other times after that). The libdispatch and the new inline block syntax were nothing short of amazing and offered the promise to finally easily access the power of multicore machines. Multicore machines have been available for a long time before that (dual processors really) but it was mainly used by pro apps such as Photoshop. In the 2000-2008 era, developers would generally only start multithreading their app when they had to, for example because a piece of work was long-running and would block the user-events run loop of the app for too long (causing the infamous spinning beach ball to appear).

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