IN WHICH Ross Rheingans-Yoo, a sometimes-poet and erstwhile student of Computer Science and Math, oc­cas­ion­al­ly writes on things of int­erest.

# Reading Feed (last update: July 9)

A collection of things that I was happy I read. Views expressed by linked authors are chosen because I think they're interesting, not because I think they're correct, unless indicated otherwise.

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Blog: Marginal Revolution | China green energy projection of the day — "China’s energy companies will make up nearly half of the new coal generation expected to go online in the next decade... Keep this all in mind the next time you hear someone tout China as the new leader of the global green energy movement."

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Blog: Marginal Revolution | Cheer you up true story from Maine — "But in Maine, servers actively campaigned to overturn the results of a November referendum raising servers’ hourly wages from $3.75 in 2016 to$12 by 2024, saying it would cause customers to tip less and actually reduce their take-home

# [CS161] The Classic CV Error

This is a very technical post, largely for the benefit of the students of CS161: Operating Systems, for which I am a Teaching Fellow this semester. It may be useful to you if you're interested in operating systems for some reason, but if you're not in a CS mood today, maybe just move along.

From what I've seen as a TF for this course, it is very, very normal to write condition-variables code that looks like this:
struct cv {
struct semaphore *sem;
volatile int waiters;
}

void cv_wait(struct cv *cv, struct lock *lock) {
KASSERT(lk_do_i_hold(lock));

cv->waiters++;
lk_release(lock);
P(cv->sem);
lk_acquire(lock);
}

void cv_broadcast(struct cv *cy struct lock *lock) {
KASSERT(lk_do_i_hold(lock));

for (; cv->waiters > 0; cv->waiters--)
V(cv->sem);
}

This code is wrong (or, more specifically, badly synchronized). And it is such a common

# [CS161] On Scheduling

This is a very technical post, largely for the benefit of the students of CS161: Operating Systems, for which I am a Teaching Fellow this semester. It may be useful to you if you're interested in operating systems for some reason, but if you're not in a CS mood today, maybe just move along.

# Why Do We Schedule, Master Bruce?

A scheduler, as you know, is responsible for determining which threads run, for how long, and in what order. As much as possible, it should give the shared illusion that each process is running constantly to completion, using the entire processor. To this end, there are three major desiderata:

• That interactive threads (in particular, user-interactive threads) are responsive.
• That no process starves.
• That the system, on average, runs quickly.

These high-level desiderata factor into the low-level conditions that:

• Threads which block expecting a response are rescheduled promptly after waking.
• Time