[Lldb-commits] [PATCH] fix lldb-mi hang on OSX

Ilia K ki.stfu at gmail.com
Tue Dec 2 09:24:56 PST 2014

Hi Zachary,

We can save file descriptor once and don't use fileno() every time we need
it but it may doesn't work and it doesn't resolve design flaw. Redesign the
lldb-mi is a big task which can take a long time.

Currently problem is that OSX's implementation of libc hangs on it in
mutex_lock() and this patch, as I understood, avoids this behaviour.
I think the 'select' patch should be committed as is.


On Tue, Dec 2, 2014 at 7:33 PM, Zachary Turner <zturner at google.com> wrote:

> I kind of feel like calling fgets from one thread and fileno from another
> thread indicates a design flaw. Is there any way to fix the design problem
> instead of this particular bug?
> On Tue, Dec 2, 2014 at 1:24 AM Илья К <ki.stfu at gmail.com> wrote:
>> Hello Abid,
>> >RE: But I am still wondering why you need extra "return" in case of
>> -exec-run. It seems to work ok on Linux. Where is it blocking in OSX?
>> I had the same bug on OSX but "select" patch helped me (btw, thank Dawn
>> for that).
>> As I understood the problem occurs when trying to get filno(stdin), when
>> another thread sleeping in fgets(stdin). The filno() starts sleeping too
>> because stdin's mutex already locked by fgets(). Perhaps it related to
>> OSX's libc implementation and therefore it don't reproduced on Linux.
>> I wrote test, which doesn't works properly without WITH_SELECT_FIX:
>> <code>
>> #include <cstdio>
>> #include <thread>
>> #include <unistd.h>
>> #include <sys/select.h>
>> //#define WITH_SELECT_FIX
>> void first_func()
>> {
>>     char buf[1024];
>>     fd_set inset;
>>     FD_ZERO(&inset);
>>     FD_SET(0, &inset);
>>     select(1, &inset, NULL, NULL, NULL);
>> #endif
>>     char *line = fgets(buf, sizeof buf, stdin);
>>     printf("you entered: %s\n", buf);
>> }
>> void second_func()
>> {
>>     usleep(100);
>>     printf("fileno: ");
>>     printf("%d\n", fileno(stdin));
>> }
>> int main()
>> {
>>     std::thread first(first_func);
>>     std::thread second(second_func);
>>     printf("start test\n");
>>     first.join();
>>     second.join();
>>     printf("exiting\n");
>>     return 0;
>> }
>> </code>
>> >RE: Btw, if the problem is only with gdb-exit then an extra check for
>> it where we check for "quit" will work too.
>> As I said above, it doesn't solve a problem, it only fixes a certain case.
>> So I think you should accept the Dawn's "select" patch.
>> Thanks,
>> Ilia
>> _______________________________________________
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>> lldb-commits at cs.uiuc.edu
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