4 ms·

Really? Go take a look at the two code snippets in "The Reentrant Kernel." I can't tell what the salient difference is supposed to be between them, much less ho

Really? Go take a look at the two code snippets in "The Reentrant Kernel." I can't tell what the salient difference is supposed to be between them, much less how they are meant to illustrate the concept of reentrancy. I mean, I appreciate the concept of what she's doing here, but that self-assessment sounds reasonable to me.

NAFV_P 12y ago
> I mean, I appreciate the concept of what she's doing here, but that self-assessment sounds reasonable to me. I would use "realistic", as opposed to "reasonable", look hard enough and you will see that everyone has gaps in their knowledge.
- probablybanned 12y ago
  That's a vacuous statement. She said "big" gaps. And I'm saying that she's making errors that no one with a background in CS (e.g. a degree) ought to make. I have no idea what your agenda is in lavishing all this unnecessary praise on Morgan Phillips, but it's gross. Please stop.
  - mrrrgn 12y ago
    I don't have any desire to be lavished in praise; but you're being unnecessarily rude I think. :[
    - probablybanned 12y ago
      Hey, I picked this username for a reason.
  - NAFV_P 12y ago
    > That's a vacuous statement. She said "big" gaps. And I'm saying that she's making errors that no one with a background in CS (e.g. a degree) ought to make. I have no idea what your agenda is in lavishing all this unnecessary praise on Morgan Phillips, but it's gross. Please stop. Is your name Linus Torvalds by any chance?
mrrrgn 12y ago
I appreciate any feedback, of course, I'm trying to learn here! About the snippets you mentioned, my reasoning was: There's a variable outside of the functions scope. If the value of the global variable were changed before it's referenced in the function the outcome would change. int global_int; int is_not_reentrant(int x) { int x = x; // An arbitrary operation return global_int + x; // the result depends on global_int } In the second, the value of the global_int is copied into a variable within the function; so the result is no longer dependent on anything outside of the function's scope. My thinking was, that this demonstrated reentrancy. int global_int; int is_reentrant(int x) { int saved = global_int; return saved + x; } From the looks of it I did make a mistake, since it seems to be missing one of these criteria. I'll modify the snippets to fix it. Thanks! :) +Must hold no static (or global) non-constant data. +Must not return the address to static (or global) non- constant data. -Must work only on the data provided to it by the caller. +Must not rely on locks to singleton resources. +Must not modify its own code (unless executing in its own unique thread storage) +Must not call non-reentrant computer programs or routines.
- probablybanned 12y ago
  Yeah, I would argue that both of those functions are re-entrant. The question is whether you can have two calls to is_not_reentrant executing concurrently without interfering with each other. So a typical example would have a non-reentrant function altering a variable like global_int as part of its computation. Also, it's important to think about the kinds of program transformations that the C compiler is free to do with your code when going from C to assembly. I think it's likely that your compiler would produce the same output for both functions. Lines of C code do not execute atomically, and instructions can be re-ordered. EDIT: Returning to this because I think I made a mistake. "Two calls executing concurrently" is not exactly right, because it admits the possibility of arbitrary instruction interleaving. A reentrant function must be able to be paused at any point, have another call to the function execute entirely, and then resume correctly. This is a weaker condition.

NAFV_P 12y ago

> I mean, I appreciate the concept of what she's doing here, but that self-assessment sounds reasonable to me. I would use "realistic", as opposed to "reasonable", look hard enough and you will see that everyone has gaps in their knowledge.

probablybanned 12y ago
That's a vacuous statement. She said "big" gaps. And I'm saying that she's making errors that no one with a background in CS (e.g. a degree) ought to make. I have no idea what your agenda is in lavishing all this unnecessary praise on Morgan Phillips, but it's gross. Please stop.
- mrrrgn 12y ago
  I don't have any desire to be lavished in praise; but you're being unnecessarily rude I think. :[
  - probablybanned 12y ago
    Hey, I picked this username for a reason.
- NAFV_P 12y ago
  > That's a vacuous statement. She said "big" gaps. And I'm saying that she's making errors that no one with a background in CS (e.g. a degree) ought to make. I have no idea what your agenda is in lavishing all this unnecessary praise on Morgan Phillips, but it's gross. Please stop. Is your name Linus Torvalds by any chance?

mrrrgn 12y ago

I appreciate any feedback, of course, I'm trying to learn here! About the snippets you mentioned, my reasoning was: There's a variable outside of the functions scope. If the value of the global variable were changed before it's referenced in the function the outcome would change. int global_int; int is_not_reentrant(int x) { int x = x; // An arbitrary operation return global_int + x; // the result depends on global_int } In the second, the value of the global_int is copied into a variable within the function; so the result is no longer dependent on anything outside of the function's scope. My thinking was, that this demonstrated reentrancy. int global_int; int is_reentrant(int x) { int saved = global_int; return saved + x; } From the looks of it I did make a mistake, since it seems to be missing one of these criteria. I'll modify the snippets to fix it. Thanks! :) +Must hold no static (or global) non-constant data. +Must not return the address to static (or global) non- constant data. -Must work only on the data provided to it by the caller. +Must not rely on locks to singleton resources. +Must not modify its own code (unless executing in its own unique thread storage) +Must not call non-reentrant computer programs or routines.

probablybanned 12y ago
Yeah, I would argue that both of those functions are re-entrant. The question is whether you can have two calls to is_not_reentrant executing concurrently without interfering with each other. So a typical example would have a non-reentrant function altering a variable like global_int as part of its computation. Also, it's important to think about the kinds of program transformations that the C compiler is free to do with your code when going from C to assembly. I think it's likely that your compiler would produce the same output for both functions. Lines of C code do not execute atomically, and instructions can be re-ordered. EDIT: Returning to this because I think I made a mistake. "Two calls executing concurrently" is not exactly right, because it admits the possibility of arbitrary instruction interleaving. A reentrant function must be able to be paused at any point, have another call to the function execute entirely, and then resume correctly. This is a weaker condition.