Allow a single-threaded program to cancel itself

There is nothing in the POSIX specification to disallow a
single-threaded program from cancelling itself, so we forcibly enable
multiple_threads to allow the next available cancellation point in the
thread to run.

Also added additional tests to cover various cancellation scenarios.

1 files changed, 3 insertions, 1 deletions

diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 68c690e88e..24a24717fc 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -378,7 +378,9 @@ extern int *__libc_pthread_init (unsigned long int *ptr,
 				 const struct pthread_functions *functions)
      internal_function;
 
-/* Variable set to a nonzero value if more than one thread runs or ran.  */
+/* Variable set to a nonzero value either if more than one thread runs or ran,
+   or if a single-threaded process is trying to cancel itself.  See
+   nptl/descr.h for more context on the single-threaded process case.  */
 extern int __pthread_multiple_threads attribute_hidden;
 /* Pointer to the corresponding variable in libc.  */
 extern int *__libc_multiple_threads_ptr attribute_hidden;