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Thread-safe just means it won't result in data corruption, race conditions or other similar issues when used from multiple threads. That's still quite different

Thread-safe just means it won't result in data corruption, race conditions or other similar issues when used from multiple threads. That's still quite different from being able to execute concurrently.

k__ 6y ago
haha, in fact "not being able to execute concurrently" is the easiest way "to ensure thread-safety" :D
- ioquatix 6y ago
  Actually, completely sequential programs can have parallelism bugs due to the underlying hardware being out of order and other such features. I know, maybe a bit of a stretch by your definitions, but I'm also not sure that "not being able to execute concurrently" implies "thread safety" in practice (even though theoretically pretty sound).
  - BubRoss 6y ago
    That would not be a bug in the software, that would be a bug in the CPU. Still, I haven't ever heard of this actually happening, do you have a link?
    - ioquatix 6y ago
      Yes, agreed, all I'm trying to say is, as software engineers we have some assumptions about processors (and compilers/interpreters) that they do things in the order we specify... but that's not always the case, and sometimes that introduces non-determinism. Processors (and compilers) are not supposed to leak the implications of their non-determinism into user code... but unfortunately it does happen. Rewriting the order of instructions sometimes happens incorrectly (which is why we need memory barriers). It's not my area, but two things that come to mind, are out-of-order execution where the CPU will re-order micro-ops, and speculative execution, where the CPU will execute one or more branches before the result of a conditional is known. Both of these issues have lead to bugs in the past and will continue to be a source of bugs in the future. https://en.wikipedia.org/wiki/Spectre_(security_vulnerability) https://en.wikipedia.org/wiki/Spectre_(security_vulnerabilit...
      - BubRoss 6y ago
        None of that has anything to do with software bugs, it doesn't change the behavior of a program. People can understand that or not, it doesn't affect the correctness of the software.

k__ 6y ago

haha, in fact "not being able to execute concurrently" is the easiest way "to ensure thread-safety" :D

ioquatix 6y ago
Actually, completely sequential programs can have parallelism bugs due to the underlying hardware being out of order and other such features. I know, maybe a bit of a stretch by your definitions, but I'm also not sure that "not being able to execute concurrently" implies "thread safety" in practice (even though theoretically pretty sound).
- BubRoss 6y ago
  That would not be a bug in the software, that would be a bug in the CPU. Still, I haven't ever heard of this actually happening, do you have a link?
  - ioquatix 6y ago
    Yes, agreed, all I'm trying to say is, as software engineers we have some assumptions about processors (and compilers/interpreters) that they do things in the order we specify... but that's not always the case, and sometimes that introduces non-determinism. Processors (and compilers) are not supposed to leak the implications of their non-determinism into user code... but unfortunately it does happen. Rewriting the order of instructions sometimes happens incorrectly (which is why we need memory barriers). It's not my area, but two things that come to mind, are out-of-order execution where the CPU will re-order micro-ops, and speculative execution, where the CPU will execute one or more branches before the result of a conditional is known. Both of these issues have lead to bugs in the past and will continue to be a source of bugs in the future. https://en.wikipedia.org/wiki/Spectre_(security_vulnerability) https://en.wikipedia.org/wiki/Spectre_(security_vulnerabilit...
    - BubRoss 6y ago
      None of that has anything to do with software bugs, it doesn't change the behavior of a program. People can understand that or not, it doesn't affect the correctness of the software.