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, 272 insertions, 0 deletions

diff --git a/lib/libpthread/thread/thr_gc.c b/lib/libpthread/thread/thr_gc.c
new file mode 100644
index 0000000..faf1b5d
--- /dev/null
+++ b/lib/libpthread/thread/thr_gc.c
@@ -0,0 +1,272 @@
+/*
+ * Copyright (c) 1998 John Birrell <jb@cimlogic.com.au>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by John Birrell.
+ * 4. Neither the name of the author nor the names of any co-contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	$Id$
+ *
+ * Garbage collector thread. Frees memory allocated for dead threads.
+ *
+ */
+#include <errno.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <pthread.h>
+#include "pthread_private.h"
+
+pthread_addr_t
+_thread_gc(pthread_addr_t arg)
+{
+	int		f_debug;
+	int		f_done = 0;
+	int		ret;
+	pthread_t	pthread;
+	pthread_t	pthread_cln;
+	pthread_t	pthread_nxt;
+	pthread_t	pthread_prv;
+	struct timespec	abstime;
+	void		*p_stack;
+
+	/* Set a debug flag based on an environment variable. */
+	f_debug = (getenv("LIBC_R_DEBUG") == NULL);
+
+	/* Set the name of this thread. */
+	pthread_set_name_np(_thread_run,"GC");
+
+	while (!f_done) {
+		/* Check if debugging this application. */
+		if (f_debug)
+			/* Dump thread info to file. */
+			_thread_dump_info();
+
+		/* Lock the thread list: */
+		_lock_thread_list();
+
+		/* Check if this is the last running thread: */
+		if (_thread_link_list == _thread_run &&
+		    _thread_link_list->nxt == NULL)
+			/*
+			 * This is the last thread, so it can exit
+			 * now.
+			 */
+			f_done = 1;
+
+		/* Unlock the thread list: */
+		_unlock_thread_list();
+
+		/*
+		 * Lock the garbage collector mutex which ensures that
+		 * this thread sees another thread exit:
+		 */
+		if (pthread_mutex_lock(&_gc_mutex) != 0)
+			PANIC("Cannot lock gc mutex");
+
+		/* No stack of thread structure to free yet: */
+		p_stack = NULL;
+		pthread_cln = NULL;
+
+		/* Point to the first dead thread (if there are any): */
+		pthread = _thread_dead;
+
+		/* There is no previous dead thread: */
+		pthread_prv = NULL;
+
+		/*
+		 * Enter a loop to search for the first dead thread that
+		 * has memory to free.
+		 */
+		while (p_stack == NULL && pthread_cln == NULL &&
+		    pthread != NULL) {
+			/* Save a pointer to the next thread: */
+			pthread_nxt = pthread->nxt_dead;
+
+			/* Check if the initial thread: */
+			if (pthread == _thread_initial)
+				/* Don't destroy the initial thread. */
+				pthread_prv = pthread;
+
+			/*
+			 * Check if this thread has detached:
+			 */
+			else if ((pthread->attr.flags &
+			    PTHREAD_DETACHED) != 0) {
+				/*
+				 * Check if there is no previous dead
+				 * thread:
+				 */
+				if (pthread_prv == NULL)
+					/*
+					 * The dead thread is at the head
+					 * of the list: 
+					 */
+					_thread_dead = pthread_nxt;
+				else
+					/*
+					 * The dead thread is not at the
+					 * head of the list: 
+					 */
+					pthread_prv->nxt_dead =
+					    pthread->nxt_dead;
+
+				/*
+				 * Check if the stack was not specified by
+				 * the caller to pthread_create and has not
+				 * been destroyed yet: 
+				 */
+				if (pthread->attr.stackaddr_attr == NULL &&
+				    pthread->stack != NULL) {
+					/*
+					 * Point to the stack that must
+					 * be freed outside the locks:
+					 */
+					p_stack = pthread->stack;
+				}
+
+				/*
+				 * Point to the thread structure that must
+				 * be freed outside the locks:
+				 */
+				pthread_cln = pthread;
+			} else {
+				/*
+				 * This thread has not detached, so do
+				 * not destroy it: 
+				 */
+				pthread_prv = pthread;
+
+				/*
+				 * Check if the stack was not specified by
+				 * the caller to pthread_create and has not
+				 * been destroyed yet: 
+				 */
+				if (pthread->attr.stackaddr_attr == NULL &&
+				    pthread->stack != NULL) {
+					/*
+					 * Point to the stack that must
+					 * be freed outside the locks:
+					 */
+					p_stack = pthread->stack;
+
+					/*
+					 * NULL the stack pointer now
+					 * that the memory has been freed: 
+					 */
+					pthread->stack = NULL;
+				}
+			}
+
+			/* Point to the next thread: */
+			pthread = pthread_nxt;
+		}
+
+		/*
+		 * Check if this is not the last thread and there is no
+		 * memory to free this time around.
+		 */
+		if (!f_done && p_stack == NULL && pthread_cln == NULL) {
+			/* Get the current time. */
+			if (clock_gettime(CLOCK_REALTIME,&abstime) != 0)
+				PANIC("gc cannot get time");
+
+			/*
+			 * Do a backup poll in 10 seconds if no threads
+			 * die before then.
+			 */
+			abstime.tv_sec += 10;
+
+			/*
+			 * Wait for a signal from a dying thread or a
+			 * timeout (for a backup poll).
+			 */
+			if ((ret = pthread_cond_timedwait(&_gc_cond,
+			    &_gc_mutex, &abstime)) != 0 && ret != ETIMEDOUT)
+				PANIC("gc cannot wait for a signal");
+		}
+
+		/* Unlock the garbage collector mutex: */
+		if (pthread_mutex_unlock(&_gc_mutex) != 0)
+			PANIC("Cannot unlock gc mutex");
+
+		/*
+		 * If there is memory to free, do it now. The call to
+		 * free() might block, so this must be done outside the
+		 * locks.
+		 */
+		if (p_stack != NULL)
+			free(p_stack);
+		if (pthread_cln != NULL) {
+			/* Lock the thread list: */
+			_lock_thread_list();
+
+			/*
+			 * Check if the thread is at the head of the
+			 * linked list.
+			 */
+			if (_thread_link_list == pthread_cln)
+				/* There is no previous thread: */
+				_thread_link_list = pthread_cln->nxt;
+			else {
+				/* Point to the first thread in the list: */
+				pthread = _thread_link_list;
+
+				/*
+				 * Enter a loop to find the thread in the
+				 * linked list before the thread that is
+				 * about to be freed.
+				 */
+				while (pthread != NULL &&
+				    pthread->nxt != pthread_cln)
+					/* Point to the next thread: */
+					pthread = pthread->nxt;
+
+				/* Check that a previous thread was found: */
+				if (pthread != NULL) {
+					/*
+					 * Point the previous thread to
+					 * the one after the thread being
+					 * freed: 
+					 */
+					pthread->nxt = pthread_cln->nxt;
+				}
+			}
+
+			/* Unlock the thread list: */
+			_unlock_thread_list();
+
+			/*
+			 * Free the memory allocated for the thread
+			 * structure.
+			 */
+			free(pthread_cln);
+		}
+		
+	}
+	return (NULL);
+}