Some small tidying up.
Chris Pressey
8 years ago
| 13 | 13 | which they write to and read from is shared between them. |
| 14 | 14 | |
| 15 | 15 | It then computes all possible interleavings of these two programs, and |
| 16 | executes them all, each on a freshly-zeroed shared memory. Unless _all_ | |
| 17 | the interleavings leave the memory in exactly the same state after execution, | |
| 18 | the programs have a race condition. | |
| 16 | executes them all, each on freshly-zeroed registers and shared memory. Unless | |
| 17 | _all_ the possible interleavings leave the memory in exactly the same state | |
| 18 | after execution, the programs have a race condition. | |
| 19 | 19 | |
| 20 | 20 | Basic Examples |
| 21 | 21 | -------------- |
| 30 | 30 | |
| 31 | 31 | PROG 1 |
| 32 | 32 | |
| 33 | INC M1 | |
| 33 | INC M0 | |
| 34 | 34 | |
| 35 | 35 | But the following two programs _do_ have a race condition: |
| 36 | 36 | |
| 59 | 59 | |
| 60 | 60 | There are two pragmas. The first, `DESC`, indicates a section of the |
| 61 | 61 | program which contains a human-readable (and computer-ignored) description |
| 62 | of the program. The other, `PROG`, specifies which program is being given | |
| 63 | next in the file. | |
| 62 | of the following program(s). This description is not free-form; it should be | |
| 63 | given in terms of comments. | |
| 64 | ||
| 65 | The other pragma, `PROG`, is followed by an integer which specifies which | |
| 66 | program is being given next in the file. | |
| 64 | 67 | |
| 65 | 68 | These pragmas are only used when the source is a single text file; |
| 66 | 69 | if the two programs are being given separately, for example in individual |
| 135 | 138 | Can you give me an example? Can you tell me about one you had to find |
| 136 | 139 | and fix?" during phone screens.) |
| 137 | 140 | |
| 138 | A huge example that is relevant to virtually every programmer is the | |
| 141 | A glaring example that is relevant to virtually every programmer is the | |
| 139 | 142 | filesystem. It's a big, shared, mutable store. There are often some |
| 140 | 143 | operations, like renaming a file, that are guaranteed to be atomic; but |
| 141 | 144 | most filesystem operations do not have this guarantee. |
| 171 | 174 | TODO |
| 172 | 175 | ---- |
| 173 | 176 | |
| 174 | * better "(can't happen)" | |
| 175 | ||
| 176 | Slightly more advanced TODO items (might not happen before release): | |
| 177 | ||
| 178 | 177 | * improve error-checking subsystem to report the program and line number |
| 179 | 178 | * better output on "Find RCs" -- explain why it failed |
| 180 | 179 | * animation style selector: staggered, black + white, no animation |