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

[Ilia K]

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.

Thanks,
Ilia

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];
>> #ifdef WITH_SELECT_FIX
>>     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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>>
>
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