PTHREAD_KEYS_MAX cleanup.

I fixed this bug a while back, but didn't remove it from the list,
could have added a better test, and could have written clearer code
that didn't require a comment.

Change-Id: Iebdf0f9a54537a7d5cbca254a5967b1543061f3d

ABI-bugs.txt

@@ -8,8 +8,5 @@ KNOWN ABI BUGS
   sigset_t is too small on ARM and x86 (but correct on MIPS), so support
   for real-time signals is broken. http://b/5828899
 
-  Too few TLS slots mean we can't allocate 128 pthread_key_t instances,
-  which POSIX says should be the minimum.
-
   atexit(3) handlers registered by a shared library aren't called on
   dlclose(3); this only affects ARM. http://b/4998315

libc/private/bionic_tls.h

@@ -30,6 +30,7 @@
 #define __BIONIC_PRIVATE_BIONIC_TLS_H_
 
 #include <sys/cdefs.h>
+#include <sys/limits.h>
 #include "__get_tls.h"
 
 __BEGIN_DECLS
@@ -74,21 +75,21 @@ enum {
 };
 
 /*
- * Maximum number of elements in the TLS array.
- * POSIX says this must be at least 128, but Android has traditionally had only 64, minus those
- * ones used internally by bionic itself.
  * There are two kinds of slot used internally by bionic --- there are the well-known slots
  * enumerated above, and then there are those that are allocated during startup by calls to
  * pthread_key_create; grep for GLOBAL_INIT_THREAD_LOCAL_BUFFER to find those. We need to manually
  * maintain that second number, but pthread_test will fail if we forget.
  */
 #define GLOBAL_INIT_THREAD_LOCAL_BUFFER_COUNT 4
+
+#define BIONIC_ALIGN(x, a) (((x) + (a - 1)) & ~(a - 1))
+
 /*
- * This is PTHREAD_KEYS_MAX + TLS_SLOT_FIRST_USER_SLOT + GLOBAL_INIT_THREAD_LOCAL_BUFFER_COUNT
- * rounded up to maintain stack alignment.
+ * Maximum number of elements in the TLS array.
+ * This includes space for pthread keys and our own internal slots.
+ * We need to round up to maintain stack alignment.
  */
-#define BIONIC_ALIGN(x, a) (((x) + (a - 1)) & ~(a - 1))
-#define BIONIC_TLS_SLOTS BIONIC_ALIGN(128 + TLS_SLOT_FIRST_USER_SLOT + GLOBAL_INIT_THREAD_LOCAL_BUFFER_COUNT, 4)
+#define BIONIC_TLS_SLOTS BIONIC_ALIGN(PTHREAD_KEYS_MAX + TLS_SLOT_FIRST_USER_SLOT + GLOBAL_INIT_THREAD_LOCAL_BUFFER_COUNT, 4)
 
 __END_DECLS
 

tests/pthread_test.cpp

@@ -33,6 +33,11 @@ TEST(pthread, pthread_key_create) {
 
 #if !defined(__GLIBC__) // glibc uses keys internally that its sysconf value doesn't account for.
 TEST(pthread, pthread_key_create_lots) {
+  // POSIX says PTHREAD_KEYS_MAX should be at least 128.
+  ASSERT_GE(PTHREAD_KEYS_MAX, 128);
+  // sysconf shouldn't return a smaller value.
+  ASSERT_GE(sysconf(_SC_THREAD_KEYS_MAX), PTHREAD_KEYS_MAX);
+
   // We can allocate _SC_THREAD_KEYS_MAX keys.
   std::vector<pthread_key_t> keys;
   for (int i = 0; i < sysconf(_SC_THREAD_KEYS_MAX); ++i) {