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Re: innobase/sync0policy.h converts opaque pthread_t to ULINT



Something similar (HAVE_IB_ATOMIC_PTHREAD_T_GCC) was removed in
2b47f8ff03845f7ffe2fa3bd583dd4123dae2b61. IIRC the reason was: relevant code
didn't follow this macro properly and this code was still functional.

You may use os_thread_pf(os_thread_get_curr_id()) to cast it to ulint. Yes, it
is unsafe. But I'd leave it this way assuming it works. This code is subject for
refactoring and I would avoid further spread of hacks.

Real fix options I could immediately think of:
- let all InnoDB threads have id based on some global counter, something like
- if all threads would have been guaranteed to have some per-thread variable
  (like my_thread_var), we could have used it's address as thread id
- SYS_gettid, but it isn't portable (see toku_os_gettid())
- add some mutex and access m_thread_id under mutex protection

The bigger problem is: this is not the only code that is accessing pthread_t
concurrently. In fact this code is probably least important of these.


On Mon, Apr 16, 2018 at 11:35:44AM +0200, Sergei Golubchik wrote:
> Hi, Teodor!
> I'd just say that this MutexDebug thing relies on pthread_t being
> ulint.
> So, I'd add a test to innodb.cmake, like, PTHREAD_T_IS_ULINT or detected
> that by the compiler in sync0policy.h. And only compiled MutexDebug is
> pthread_t is ulint. Or, at least, sizeof(pthread_t) == sizeof(ulint).
> On Apr 16, Teodor Mircea Ionita wrote:
> > Hi,
> > 
> > While trying to build on macOS 10.13.4 with clang 9.1.0 I originally came across this error:
> > --
> > .../storage/innobase/include/sync0policy.h:79:4: error: cannot initialize a parameter of type 'int64' (aka 'long long') with
> >      an rvalue of type 'os_thread_id_t' (aka '_opaque_pthread_t *')
> >                        my_atomic_storelint(&m_thread_id, os_thread_get_curr_id());
> > ---
> > This problem was originally reported in MDEV-15778. Since pthread_t on macOS is a pointer to a struct named  _opaque_pthread_t, the "obvious" solution for this was to explicitly cast to ULINT which in turn is defined as size_t, fine so far. Solution was tested in PR#691.
> > 
> > However, upon testing my patch with buildbot, on slave kvm-fulltest2, which is 64bit qemu vm with Ubuntu precise-i386 (32bit) running and gcc compiling in -march=i686. The above "fix" now yields:
> > --
> > /home/buildbot/buildbot/build/mariadb-10.3.6/storage/innobase/include/sync0policy.h:79:4: error: invalid cast from type ‘os_thread_id_t {aka long unsigned int}’ to type ‘ulint {aka unsigned int}’
> > ---
> > 
> > Now reconsidering more carefully, this looks more serious then initially thought, posix pthread_t(3) is defined as:
> > --
> > POSIX.1 allows an implementation wide freedom in choosing the type used to represent a thread ID; for example, representation using either an arithmetic type or a structure is permitted. Therefore, variables of type pthread_t can't portably be compared using the C equality operator (==); use pthread_equal(3)instead.
> > ---
> > 
> > So in this particular platform spec, where pthread_t on Linux is defined as unsigned long int integral type and if LP64 model is used, this implies pthread_t always being 64bit in either both 32 and 64 arch and trying to convert to size_t on a 32bit arch will fail.
> > 
> > Now given that the standard particularly states pthread_t as being opaque and no assumptions should be made in regards to the actual type, not even an initializer type (which ULINT_UNDEFINED defines as -1), trying to cast m_thread_id to any other type ( (ULINT) ) either implicitly or explicit is not portable. Is this a bug that needs fixing or just impossible to handle pthread id atomically in any other fashion? How about a test case I can run to confirm/infirm erratic behavior?
> > 
> > Since I don't have access to the particular bb slave instance to check with sizeof() maybe somebody else can help me here to confirm this? Relevant links bellow:
> > 
> > https://jira.mariadb.org/browse/MDEV-15778
> > https://buildbot.askmonty.org/buildbot/builders/kvm-fulltest2/builds/12317/steps/compile/logs/stdio
> > https://linux.die.net/man/3/pthread_self
> > https://github.com/MariaDB/server/pull/691
> > 
> > Cheers,
> > Teodor
> Regards,
> Sergei
> Chief Architect MariaDB
> and security@xxxxxxxxxxx
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