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* [newlib-cygwin] Cygwin: pthreads: iterate over key destructors per POSIX
@ 2020-08-30 12:29 Corinna Vinschen
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From: Corinna Vinschen @ 2020-08-30 12:29 UTC (permalink / raw)
To: cygwin-cvs
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=b9ad0fbf286ada6cdb6b86f351196369cf703c73
commit b9ad0fbf286ada6cdb6b86f351196369cf703c73
Author: Corinna Vinschen <corinna@vinschen.de>
Date: Sat Aug 29 21:08:31 2020 +0200
Cygwin: pthreads: iterate over key destructors per POSIX
POSIX requires that key destructors are called in a loop
for each key with a non-NULL value until all values are
NULL, or until all destructors for non-NULL values
have been called at least PTHREAD_DESTRUCTOR_ITERATIONS
(per POSIX: 4) times.
Cygwinonly called all destructors with non-NULL values
exactly once. This patch fixes Cygwin to follow POSIX.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Diff:
---
winsup/cygwin/include/limits.h | 7 +------
winsup/cygwin/thread.cc | 4 ++++
winsup/cygwin/thread.h | 20 +++++++++++++++++++-
3 files changed, 24 insertions(+), 7 deletions(-)
diff --git a/winsup/cygwin/include/limits.h b/winsup/cygwin/include/limits.h
index 524a469e4..6a55578f3 100644
--- a/winsup/cygwin/include/limits.h
+++ b/winsup/cygwin/include/limits.h
@@ -225,13 +225,8 @@ details. */
/* Maximum number of attempts made to destroy a thread's thread-specific
data values on thread exit. */
-/* FIXME: I really don't understand this value. Why should multiple
- attempts be necessary to destroy thread-specific data?!? Anyway, the
- current value here is 1, taken originally from our pthread.h file,
- where it was mistakenly defined first. Unfortunately this value is
- lower than the POSIX defined minimum value, which is 4. */
#undef PTHREAD_DESTRUCTOR_ITERATIONS
-#define PTHREAD_DESTRUCTOR_ITERATIONS 1
+#define PTHREAD_DESTRUCTOR_ITERATIONS 4
/* Maximum number of data keys that can be created by a process. */
/* Tls has 1088 items - and we don't want to use them all :] */
diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index e09507e07..617be57c2 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -1713,6 +1713,8 @@ pthread_key::_fixup_after_fork ()
set (fork_buf);
}
+bool pthread_key::iterate_dtors_once_more;
+
void
pthread_key::run_destructor ()
{
@@ -1723,6 +1725,8 @@ pthread_key::run_destructor ()
{
set (NULL);
destructor (oldValue);
+ if (get ())
+ iterate_dtors_once_more = true;
}
}
}
diff --git a/winsup/cygwin/thread.h b/winsup/cygwin/thread.h
index 4c6557aef..c574a3915 100644
--- a/winsup/cygwin/thread.h
+++ b/winsup/cygwin/thread.h
@@ -197,6 +197,7 @@ protected:
class pthread_key: public verifyable_object
{
DWORD tls_index;
+ static bool iterate_dtors_once_more;
public:
static bool is_good_object (pthread_key_t const *);
@@ -218,7 +219,24 @@ public:
static void run_all_destructors ()
{
- keys.for_each (&pthread_key::run_destructor);
+ /* POSIX requires at least four iterations of running destructors:
+
+ If, after all the destructors have been called for all non-NULL
+ values with associated destructors, there are still some non-NULL
+ values with associated destructors, then the process is repeated.
+ If, after at least {PTHREAD_DESTRUCTOR_ITERATIONS} iterations of
+ destructor calls for outstanding non-NULL values, there are still
+ some non-NULL values with associated destructors, implementations
+ may stop calling destructors, or they may continue calling
+ destructors until no non-NULL values with associated destructors
+ exist, even though this might result in an infinite loop. */
+ for (int i = 0; i < PTHREAD_DESTRUCTOR_ITERATIONS; ++i)
+ {
+ iterate_dtors_once_more = false;
+ keys.for_each (&pthread_key::run_destructor);
+ if (!iterate_dtors_once_more)
+ break;
+ }
}
/* List support calls */
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