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Allow caller to block signals.

Greetings,

We use libunwind just for stack traces (I suspect many others do as well).

The use pattern is:

GetStackTrace(void** result, int max_depth)
{
...
  unw_getcontext(&uc);
  unw_init_local(&cursor, &uc);

  while (n < max_depth) {
    if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) {
      break;
    }
    result[n++] = ip;
    if (unw_step(&cursor) <= 0) {
      break;
    }
  }

Given this usage, it is quite convenient for us to block signals (or
prevent signal handlers from re-entering libunwind by other means) at the
"top level", which makes most of the sigprocmask calls performed by
libunwind itself unneccessary.

The second patch in this series adds a configure option which removes most
of the sigprocmask calls.

Attached patch is a preliminary for it -- consolidating all of the
"sigprocmask; mutex_lock;" sequences into lock_acquire and "mutex_unlock;
sigprocmask;" sequences into lock_release.

Thanks,
--
Paul Pluzhnikov

commit 402d15b123d54a7669db7cf17a76dd315094e472
Author: Paul Pluzhnikov <ppluzhnikov@google.com>
Date:   Mon Sep 21 10:18:28 2009 -0700

    Replace "sigprocmask + mutext_lock" with a single lock_acquire.
    Likewise, replace "mutext_unlock + sigprocmask" with lock_release.
This commit is contained in:
Paul Pluzhnikov 2009-09-21 12:02:07 -07:00 committed by Arun Sharma
parent 35e6a1a108
commit 84d4150668
10 changed files with 20 additions and 40 deletions

View file

@ -44,8 +44,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&arm_lock);
lock_acquire (&arm_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -61,6 +60,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&arm_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&arm_lock, saved_mask);
}

View file

@ -489,11 +489,10 @@ get_rs_cache (unw_addr_space_t as, intrmask_t *saved_maskp)
if (AO_test_and_set (&cache->busy) == AO_TS_SET)
return NULL;
# else
sigprocmask (SIG_SETMASK, &unwi_full_mask, saved_maskp);
if (likely (caching == UNW_CACHE_GLOBAL))
{
Debug (16, "%s: acquiring lock\n", __FUNCTION__);
mutex_lock (&cache->lock);
lock_acquire (&cache->lock, *saved_maskp);
}
# endif
#endif
@ -521,8 +520,7 @@ put_rs_cache (unw_addr_space_t as, struct dwarf_rs_cache *cache,
AO_CLEAR (&cache->busy);
# else
if (likely (as->caching_policy == UNW_CACHE_GLOBAL))
mutex_unlock (&cache->lock);
sigprocmask (SIG_SETMASK, saved_maskp, NULL);
lock_release (&cache->lock, *saved_maskp);
# endif
#endif
}

View file

@ -35,8 +35,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&hppa_lock);
lock_acquire (&hppa_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -52,6 +51,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&hppa_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&hppa_lock, saved_mask);
}

View file

@ -71,8 +71,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&unw.lock);
lock_acquire (&unw.lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -120,6 +119,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&unw.lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&unw.lock, saved_mask);
}

View file

@ -113,11 +113,10 @@ get_script_cache (unw_addr_space_t as, intrmask_t *saved_maskp)
if (AO_test_and_set (&cache->busy) == AO_TS_SET)
return NULL;
# else
sigprocmask (SIG_SETMASK, &unwi_full_mask, saved_maskp);
if (likely (caching == UNW_CACHE_GLOBAL))
{
Debug (16, "%s: acquiring lock\n", __FUNCTION__);
mutex_lock (&cache->lock);
lock_acquire (&cache->lock, *saved_maskp);
}
# endif
#endif
@ -144,8 +143,7 @@ put_script_cache (unw_addr_space_t as, struct ia64_script_cache *cache,
AO_CLEAR (&cache->busy);
# else
if (likely (as->caching_policy == UNW_CACHE_GLOBAL))
mutex_unlock (&cache->lock);
sigprocmask (SIG_SETMASK, saved_maskp, NULL);
lock_release (&cache->lock, *saved_maskp);
# endif
#endif
}

View file

@ -44,8 +44,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&mips_lock);
lock_acquire (&mips_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -61,6 +60,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&mips_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&mips_lock, saved_mask);
}

View file

@ -115,8 +115,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&ppc32_lock);
lock_acquire (&ppc32_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -132,6 +131,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&ppc32_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&ppc32_lock, saved_mask);
}

View file

@ -162,8 +162,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&ppc64_lock);
lock_acquire (&ppc64_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -179,6 +178,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&ppc64_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&ppc64_lock, saved_mask);
}

View file

@ -47,8 +47,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&x86_lock);
lock_acquire (&x86_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -64,6 +63,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&x86_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&x86_lock, saved_mask);
}

View file

@ -61,8 +61,7 @@ tdep_init (void)
sigfillset (&unwi_full_mask);
sigprocmask (SIG_SETMASK, &unwi_full_mask, &saved_mask);
mutex_lock (&x86_64_lock);
lock_acquire (&x86_64_lock, saved_mask);
{
if (!tdep_needs_initialization)
/* another thread else beat us to it... */
@ -78,6 +77,5 @@ tdep_init (void)
tdep_needs_initialization = 0; /* signal that we're initialized... */
}
out:
mutex_unlock (&x86_64_lock);
sigprocmask (SIG_SETMASK, &saved_mask, NULL);
lock_release (&x86_64_lock, saved_mask);
}