Move the cleanup code that frees memory allocated for a dead thread from

the thread kernel into a garbage collector thread which is started when
the fisrt thread is created (other than the initial thread). This
removes the window of opportunity where a context switch will cause a
thread that has locked the malloc spinlock, to enter the thread kernel,
find there is a dead thread and try to free memory, therefore trying
to lock the malloc spinlock against itself.

The garbage collector thread acts just like any other thread, so
instead of having a spinlock to control accesses to the dead thread
list, it uses a mutex and a condition variable so that it can happily
wait to be signalled when a thread exists.

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/libc_r/uthread/uthread_init.c b/lib/libc_r/uthread/uthread_init.c
index 69b0fef..50f3bef 100644
--- a/lib/libc_r/uthread/uthread_init.c
+++ b/lib/libc_r/uthread/uthread_init.c
@@ -251,6 +251,11 @@ _thread_init(void)
 	__set_dynamic_handler_allocator( dynamic_allocator_handler_fn );
 #endif /* GCC_2_8_MADE_THREAD_AWARE */
 
+	/* Initialise the garbage collector mutex and condition variable. */
+	if (pthread_mutex_init(&_gc_mutex,NULL) != 0 ||
+	    pthread_cond_init(&_gc_cond,NULL) != 0)
+		PANIC("Failed to initialise garbage collector mutex or condvar");
+
 	return;
 }