Chapter 9 - Expect the Unexpected
Any function you call may not work as you expect.
• If you are lucky, it will return an error code to signal this. (p.69)
p.70:
- understand basic concurrency principles
- Understand mechanisms to reliably and quickly pass messages between thread contexts without introducing race conditions or blocking the threads unnecessarily
- Shutdown:
- how to bring the code to a graceful halt without leaking resources, locking up, or crashing
- especially hard in a multithreaded system
- don't leave one object attempting to use or return to another that has been deleted
Chapter 10 - Bug Hunting
- Lay Traps: Add assertions or tests to verify the system invariants—the facts that must hold for the state to be correct. (p.78)
- Binary Chop: (p.78)
- Work out the start of a chain of events.
- Work out the end
- Check middle point
- if good, then start to middle is good, so check midpoint of here to end
- if bad, then check midpoint of start to this point
- Software Archaeology
- Look thru your version control to find the last time this bug didn't exist
- Binary chop through time to find where bug was introduced
- Use a code coverage tool to inspect how much of your code is actually covered by tests. (p.79)
- Once you find the bug:
- Write a simple test that demonstrates the bug.
- Add it to the test suite before you fix the code.
- Use the test to:
- prove bug is fixed
- test to prevent bug from reoccurring
- Analyze/look for related bugs
- Are there more bugs in the section where you found this one?
- Was bug in a repeated code pattern that's used elsewhere?
- Note in which parts of the code you're finding more bugs.
- Part of code that's used most often?
- Weakness in that particular section of the software?
- Non-Reproducible Bugs
- Keep records that may eventually help you come up with theories you can test to possibly find the cause.
- Add more assertions and log statements -- preferably into your beta or release builds.
- Automate a test farm to run long-running soak tests.
- Common situations leading to hard-to-reproduce bugs:
- Threads
- "Heisenbugs" - disappear when you add log statements
- Network interacation
- Speed to access database, disk, other storage can vary
- Memory corruption
- Global variables
Chapter 2
- KEY ➤ Remember who you’re writing code for: other people. (p.9)
- page 10:
Some programmers like to present banner comments in pretty ASCII-art boxes:
/**************************************************
* This is a pretty comment. *
* Note that there are asterisks on the *
* righthand side of the box. Wow; it looks neat. *
* Hope I never have to fix this tiypo. *
**************************************************/
...Frankly, this is a sadistic presentation style.
- Also on p.10, he says to write code as you would prose. "Functions are akin to chapters."
- Within the chapters, related lines of code are equivalent to paragraphs.
- Insert blank lines only between these conceptual paragraphs, not within them
- Don't have too many of these "paragraphs" per function
- If you clean up code, make that a separate commit from any changes to the code's behavior.
KEY ➤ Never alter presentation and behaviour at the same time. Make
them separate version-controlled changes. (p.14)
Chapter 3
- (p.18) There are many reasons why unnecessary code is the root of all evil...
- Writing a fresh line of code is the birth of a little life form.
- ...
- Code harbours bugs. The more code you have, the more places there are for bugs
to hide.
- Refactoring (p.20)
- A refactor is only a refactor if it is a transformation of the source code, preserving behaviour.
- the DRY principle: Don’t Repeat Yourself!
- ...factoring similar code into a shared function introduces tight coupling...
They both now rely on a shared interface;...
—so DRY your code responsibly! (p.21)
- Dead code is code that is never run, that can never be reached...
- Tell your code to get a life, or get lost. (p.23)
- The code itself says what and how. A comment should explain why..(p.24)
- Do not remove code by commenting it out. (p.24)
- Remove code completely.
- You can always get it back afterwards from your source control
system.
Chapter 4
- YAGNI = You Aren’t Gonna Need It: (p.29)
- Don't write..code you think is going to be needed in future versions.
- Don’t write it now if you don’t need it now.
- Much "debug" code is necrotic...unsightly scaffolding that hides the beautiful architecture underneath. (p.31)
- It is harder to refactor, simplify, or optimise your program when it is bogged down
by zombie code. (p.32)
- Don’t add “minor”features that you think are interesting, but no one has asked for. They’ll be easy enough to add later, if they are required. Even if it seems like a good idea. Don’t do it. (p.33) That one is hard to resist. :^)
Chapter 6
- ...try adding a single, one-line, failing test. Does the test suite immediately fail? This smoke test proves that the tests are not actively being ignored. (p.50)
Chapter 7
- I know I shouldn’t moan, but sometimes I swear that programmers shouldn’t be allowed
to type the word thread without first obtaining a license to wield such a dangerous
weapon. (p.56)
- ...if it has been working adequately for years without tinkering, it is probably inappropriate to “tidy it up” now, especially if you’re unlikely to need to make many more changes in the future. (p.58)
- KEY ➤ Make code changes slowly, and carefully. Make one change at a time. (p.58)
- ...the unreadable mess of special cases might be like that for a reason. Each bodge and code hack encodes an important piece of functionality that has been uncovered through bitter
experience. Ignore these subtle behaviours at your peril. (p.59)
- The effective programmer does not only deal well with the bad code, but also with the people that wrote it. (p.60)
- “refactored the code to look neater.” -> “refactored code back to working.” (p.60)
Chapter 8:
- Don't ignore:
- Return codes - e.g. printf
- Side effects - e.g. errno - which is a mess when code is threaded
- Exceptions
try
{
// ...do something...
}
catch (...) {} // ignore errors
The saving grace of this awful construct is that it highlights the fact you’re doing
something morally dubious. (p.64)
- Understand your language’s idioms and requirements for effective exception use. (p.65)
