"Nadav Har'El" <n...@cloudius-systems.com> writes: > First of all, thanks. This indeed fixes the bug, and is exactly the first > patch I tried to fix it this problem.
> I want to explain, though, why I ended up sending a different patch for > this problem - a 4-line patch instead of this one-liner. The explanation is > not very important, and I should probably have done this earlier, but > perhaps someone would find it interesting. > When the user types ^C, the operating system sends SIGINT to all processes > belonging to the terminal's process group - and in particular it sends > SIGINT to *both* the child compiler and ccache, separately. > Your patch makes ccache exit as soon as it gets the SIGINT - but the child > compiler might still be running for a while longer. This will usually be > fine, but I thought the user can be surprised if he sees ccache (which he > considers to be the compiler) exit, but "ps" shows the compiler is still > running. This would be especially annoying if some hypothetical compiler > trapped SIGINT deliberately, and continued to run long after ccache exits. Actually, that's a bug not just a cosmetic problem, because it introduces a race condition. Consider this sequence of events: * make launches "ccache gcc -o test.o test.c" * user types control-C * ccache receives SIGINT and exits * make does unlink("test.o") to clean up after failed compile step, which it thinks is done * gcc creates test.o * gcc receives SIGINT and exits We're left with a probably-broken test.o in the filesystem, despite make's attempt to clean up. Now, the window for this is pretty narrow, but I think it could happen: I don't believe that sending signals to multiple processes is atomic in most kernels. You really don't want ccache to exit until after all externally-observable things have stopped happening. (I recently fixed a somewhat related bug in Postgres :-(, which is why this caught my eye.) regards, tom lane _______________________________________________ ccache mailing list firstname.lastname@example.org https://lists.samba.org/mailman/listinfo/ccache