[PATCH 2/2] Add support for LinuxThreads.

Jason Evans jasone at canonware.com
Tue Oct 22 13:47:09 PDT 2013

On Oct 22, 2013, at 1:31 PM, Leonard Crestez <lcrestez at ixiacom.com> wrote:
> On 10/22/2013 11:16 PM, Jason Evans wrote:
>> On Oct 21, 2013, at 2:12 PM, Leonard Crestez <lcrestez at ixiacom.com> wrote:
>>> When using LinuxThreads pthread_setspecific triggers recursive allocation on all threads. Work around this by creating a global linked list of in-progress tsd initializations.
>>> This modifies the _tsd_get_wrapper macro-generated function. When it has
>>> to initialize an TSD object it will push the item to the linked list
>>> first. If this causes a recursive allocation then the _get_wrapper
>>> request is satisfied from the list. When pthread_setspecific returns the item is removed from the list.
>>> This effectively adds a very poor substitute for real TLS used only
>>> during pthread_setspecific allocation recursion.
>>> Signed-off-by: Crestez Dan Leonard <lcrestez at ixiacom.com>
>>> ---
>>>  include/jemalloc/internal/tsd.h | 63 +++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 63 insertions(+)
>> I don't see how this code can work.  It stack-allocates block (struct tsd_init_block block;), then permanently links it into a ring.  There are other less critical issues (e.g. no cleanup during thread exit, using pthread_mutex_t rather than malloc_mutex_t, and coding style conformance), but let's worry first about whether there's a feasible way to restructure the initialization code.
> Hello,
> The link is not permanent, it is temporary until pthread_setspecific returns. The stack-allocated block is inserted in the list by tsd_init_checkrec and removed by tsd_init_finish, immediately after pthread_setspecific returns. It is allocated on the stack because the lifetime is so short. Unless a lot of threads are created the list will only contain at most one item during the first allocation on each thread.

Ah, I misread the ring removal code in tsd_init_finish().

> I can replace pthread_mutex_t. What should I fix about the coding style to make it acceptable? Should I move the tsd_init_* inside the malloc_tsd_funcs macro or to some separate file?

Hmm, there numerous minor style issues, but I don't want to take up a bunch of your time trying to deal with that.  I'll take it from here.  For future patches, take a look at FreeBSD's style(9) manual page (http://www.freebsd.org/cgi/man.cgi?query=style) for guidance.


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