31–40 of 83 posts
Earlier quoted context omitted.
there are two hard things in computer science: cache invalidation, naming things, and off-by-one errors
there are three hard things concurrency, in computer science: cache invalidation, naming things, and off-by-one errors
https://github.com/torvalds/linux/blob/d158fc7f36a25e19791d2... Variables `three`, `five` and `seven` are better described as `next_power_of_three`, `next_power_of_five` and `next_power_of_seven`. Since the `ext4_list_backups` function should iterate through 1 (= 3^0 = 5^0 = 7^0), 3, 5, 7, 3^2, 5^2, 3^3, 7^2, ... and 1 should not repeat three times, the initial value of `next_power_of_three` (or any of others) should…
A perfect example of a missing code-comment.
Read the comment above ext4_list_backups right above: https://github.com/torvalds/linux/blob/d158fc7f36a25e19791d2... /* * Iterate through the groups which hold BACKUP superblock/GDT copies in an * ext4 filesystem. The counters should be initialized to 1, 5, and 7 before * calling this for the first time. In a sparse filesystem it will be the * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ... * F…
If I'm not mistaken, the first number (1) is not considered a power of three, hence the initial (seemingly strange) three=1. See http://www.nongnu.org/ext2-doc/ext2.pdf#page15 for a slightly more detailed explanation. "The first version of ext2 (revision 0) stores a copy at the start of every block group, along with backups of the group descriptor block(s). Because this can consume a considerable amount of space for…
If only there was a system for fixing the code yourself instead of having to post about it to a widely read tech site.
> There are only two hard things in Computer Science: cache invalidation and naming things. > -- Phil Karlton
I've always thought that the "naming things" refers to the more subtle problem of giving things unique identifiers in distributed systems, rather than coming up with variable names. "Naming things" includes systems like MAC address allocation, IP address allocation, DNS, URLs for documents, process IDs, name to inode mapping in filesystems, autoincrement primary keys in databases, etc. Any ideas on what Karlton reall…
>The difficulty only arises if the body of a nested function refers directly (i.e., not via argument passing) to identifiers defined in the environment in which the function is defined, but not in the environment of the function call.
Also, the version I know has much more bite:
>There is also a variation on this that says there are two hard things in computer science: cache invalidation, naming things, and off-by-one errors.
Earlier quoted context omitted.
I've always thought that the "naming things" refers to the more subtle problem of giving things unique identifiers in distributed systems, rather than coming up with variable names. "Naming things" includes systems like MAC address allocation, IP address allocation, DNS, URLs for documents, process IDs, name to inode mapping in filesystems, autoincrement primary keys in databases, etc. Any ideas on what Karlton reall…
I always assumed it was the more general "coming up with names" - for variables, hostnames, project names etc. The non-human-readable things like MACs, IPs and auto-increment keys are easy. But when I have to come up with a short, memorable and non-confusing name for something like a script that can take me longer than writing the code.
For example, how to assign unique MAC numbers to network cards without a centralised database that has to be modified for each card manufactured? Vendors get address space blocks, and probably split these further into blocks for factories and production lines.
Generating unique autoincrement row numbers in a distributed database or process IDs in a cluster is also a complex problem if it has to be faster than any communication between the nodes.
Designing the layout of IP addresses, architecture of DHCP and DNS, and the very idea of URLs are fantastic pieces of Computer Science work. Easy to use, but a hard problem for the original designers!
But of course, I have no idea what Karlton had in mind with the quote. "Naming things" as "assigning unique identifiers" always felt appropriate with cache invalidation, as both are problems that are easy for single cores/machines, but very complex in distributed systems.
Earlier quoted context omitted.
More like a terribly named variable.
Agreed, comments are generally a way to compensate failure to express ourselves in the code (in this case bad naming).
The goal is to enumerate the powers of 3, 5, and 7, once each. Since power sequences all overlap at x^0 = 1, but we specifically don't want to enumerate 1 three times, we have to give one (or, from an alternative viewpoint, two) of the variables special treatment. Whether you name the variables "three", "five", and "seven", or "next_power_of_three", "next_power_of_five", and "next_power_of_seven", you're doing something strange by starting one of them at 1 and the other two past 1, and that should be commented on. The naming-only solution "powers_of_three_initialized_starting_at_three_to_the_zeroeth", "powers_of_five_initialized_starting_at_five_to_the_first", and "powers_of_seven_initialized_starting_at_seven_to_the_first", is hilariously awful, and still requires a comment to explain why the threes variable is more (or less) special than the other two.
Read the comment above ext4_list_backups right above: https://github.com/torvalds/linux/blob/d158fc7f36a25e19791d2... /* * Iterate through the groups which hold BACKUP superblock/GDT copies in an * ext4 filesystem. The counters should be initialized to 1, 5, and 7 before * calling this for the first time. In a sparse filesystem it will be the * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ... * F…
See this comment: https://news.ycombinator.com/item?id=7296586 Good commenting is no substitute for good naming. For a variable containing the number 1, "three" is a shitty name.
If I adjust your comment to "for a variable whose only purpose is to be passed to another function as the parameter called 'three', 'three' is a shitty name", would you endorse that sentiment?
Earlier quoted context omitted.
If I'm not mistaken, the first number (1) is not considered a power of three, hence the initial (seemingly strange) three=1. See http://www.nongnu.org/ext2-doc/ext2.pdf#page15 for a slightly more detailed explanation. "The first version of ext2 (revision 0) stores a copy at the start of every block group, along with backups of the group descriptor block(s). Because this can consume a considerable amount of space for…
1 is the zeroth power of 3