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guard.cc: Fix comments.

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2011-05-26  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* libsupc++/guard.cc: Fix comments.

From-SVN: r174241
This commit is contained in:
Jonathan Wakely 2011-05-25 23:43:32 +00:00 • committed by Jonathan Wakely
parent 2b4e07b814
commit 50aeb6f48c
2 changed files with 19 additions and 15 deletions
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4
libstdc++-v3/ChangeLog
View file

@ -1,3 +1,7 @@
2011-05-26 Jonathan Wakely <jwakely.gcc@gmail.com>
* libsupc++/guard.cc: Fix comments.
2011-05-25 Ian Lance Taylor <iant@google.com>
PR libstdc++/49060

30
libstdc++-v3/libsupc++/guard.cc
View file

@ -85,7 +85,7 @@ namespace
# if defined(__GTHREAD_HAS_COND) && !defined(_GLIBCXX_USE_FUTEX)
namespace
{
// A single conditional variable controlling all static initializations.
// A single condition variable controlling all static initializations.
static __gnu_cxx::__cond* static_cond;
// using a fake type to avoid initializing a static class.
@ -136,7 +136,7 @@ __set_and_release (__cxxabiv1::__guard *g)
#endif /* __GTHREADS */
//
// Here are C++ run-time routines for guarded initiailization of static
// Here are C++ run-time routines for guarded initialization of static
// variables. There are 4 scenarios under which these routines are called:
//
// 1. Threads not supported (__GTHREADS not defined)
@ -147,24 +147,24 @@ __set_and_release (__cxxabiv1::__guard *g)
//
// The old code supported scenarios 1-3 but was broken since it used a global
// mutex for all threads and had the mutex locked during the whole duration of
// initlization of a guarded static variable. The following created a dead-lock
// with the old code.
// initialization of a guarded static variable. The following created a
// dead-lock with the old code.
//
// Thread 1 acquires the global mutex.
// Thread 1 starts initializing static variable.
// Thread 1 creates thread 2 during initialization.
// Thread 2 attempts to acuqire mutex to initialize another variable.
// Thread 2 attempts to acquire mutex to initialize another variable.
// Thread 2 blocks since thread 1 is locking the mutex.
// Thread 1 waits for result from thread 2 and also blocks. A deadlock.
//
// The new code here can handle this situation and thus is more robust. Howere,
// we need to use the POSIX thread conditional variable, which is not supported
// The new code here can handle this situation and thus is more robust. However,
// we need to use the POSIX thread condition variable, which is not supported
// in all platforms, notably older versions of Microsoft Windows. The gthr*.h
// headers define a symbol __GTHREAD_HAS_COND for platforms that support POSIX
// like conditional variables. For platforms that do not support conditional
// like condition variables. For platforms that do not support condition
// variables, we need to fall back to the old code.
// If _GLIBCXX_USE_FUTEX, no global mutex or conditional variable is used,
// If _GLIBCXX_USE_FUTEX, no global mutex or condition variable is used,
// only atomic operations are used together with futex syscall.
// Valid values of the first integer in guard are:
// 0 No thread encountered the guarded init
@ -211,7 +211,7 @@ namespace __cxxabiv1
#endif
}
// acuire() is a helper function used to acquire guard if thread support is
// acquire() is a helper function used to acquire guard if thread support is
// not compiled in or is compiled in but not enabled at run-time.
static int
acquire(__guard *g)
@ -284,7 +284,7 @@ namespace __cxxabiv1
{
// The guarded static is currently being initialized by
// another thread, so we release mutex and wait for the
// conditional variable. We will lock the mutex again after
// condition variable. We will lock the mutex again after
// this.
get_static_cond().wait_recursive(&get_static_mutex());
}
@ -295,7 +295,7 @@ namespace __cxxabiv1
}
# else
// This provides compatibility with older systems not supporting
// POSIX like conditional variables.
// POSIX like condition variables.
if (acquire(g))
{
mw.unlock = false;
@ -335,7 +335,7 @@ namespace __cxxabiv1
set_init_in_progress_flag(g, 0);
// If we abort, we still need to wake up all other threads waiting for
// the conditional variable.
// the condition variable.
get_static_cond().broadcast();
return;
}
@ -344,7 +344,7 @@ namespace __cxxabiv1
set_init_in_progress_flag(g, 0);
#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
// This provides compatibility with older systems not supporting POSIX like
// conditional variables.
// condition variables.
if (__gthread_active_p ())
static_mutex->unlock();
#endif
@ -385,7 +385,7 @@ namespace __cxxabiv1
#if defined(__GTHREADS) && !defined(__GTHREAD_HAS_COND)
// This provides compatibility with older systems not supporting POSIX like
// conditional variables.
// condition variables.
if (__gthread_active_p())
static_mutex->unlock();
#endif