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Mention dl_load_lock by name in the comments

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Mention dl_load_lock by name instead of just 'load lock' in the
comments.  This makes it unambigious which lock we're talking about.
This commit is contained in:
Siddhesh Poyarekar 2015-07-24 06:09:47 +05:30
parent b301e68e4b
commit a81a00ff94
2 changed files with 15 additions and 9 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2015-07-24 Siddhesh Poyarekar <siddhesh@redhat.com>
* stdlib/cxa_thread_atexit_impl.c: Use the lock name dl_load_lock
instead of just saying load lock in the comments.
2015-07-23 Roland McGrath <roland@hack.frob.com>
* sysdeps/unix/Subdirs: Moved ...

19
stdlib/cxa_thread_atexit_impl.c
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@ -25,14 +25,15 @@
combinations of all three functions are the link map list, a link map for a
DSO and the link map member l_tls_dtor_count.
__cxa_thread_atexit_impl acquires the load_lock before accessing any shared
state and hence multiple of its instances can safely execute concurrently.
__cxa_thread_atexit_impl acquires the dl_load_lock before accessing any
shared state and hence multiple of its instances can safely execute
concurrently.
_dl_close_worker acquires the load_lock before accessing any shared state as
well and hence can concurrently execute multiple of its own instances as
_dl_close_worker acquires the dl_load_lock before accessing any shared state
as well and hence can concurrently execute multiple of its own instances as
well as those of __cxa_thread_atexit_impl safely. Not all accesses to
l_tls_dtor_count are protected by the load lock, so we need to synchronize
using atomics.
l_tls_dtor_count are protected by the dl_load_lock, so we need to
synchronize using atomics.
__call_tls_dtors accesses the l_tls_dtor_count without taking the lock; it
decrements the value by one. It does not need the big lock because it does
@ -51,8 +52,8 @@
it is safe to unload the DSO. Hence, to ensure that this does not happen,
the following conditions must be met:
1. In _dl_close_worker, the l_tls_dtor_count load happens before the DSO
is unload and its link map is freed
1. In _dl_close_worker, the l_tls_dtor_count load happens before the DSO is
unloaded and its link map is freed
2. The link map dereference in __call_tls_dtors happens before the
l_tls_dtor_count dereference.
@ -122,7 +123,7 @@ __cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_symbol)
/* This increment may only be concurrently observed either by the decrement
in __call_tls_dtors since the other l_tls_dtor_count access in
_dl_close_worker is protected by the load lock. The execution in
_dl_close_worker is protected by the dl_load_lock. The execution in
__call_tls_dtors does not really depend on this value beyond the fact that
it should be atomic, so Relaxed MO should be sufficient. */
atomic_fetch_add_relaxed (&lm_cache->l_tls_dtor_count, 1);