Fix mutex pretty printer test and pretty printer output.

This fixes the mutex pretty printer so that, if the owner ID isn't recorded
(such as in the current lock elision implementation), "Owner ID" will be shown
as "Unknown" instead of 0. It also changes the mutex printer output so that it
says "Acquired" instead of "Locked". The mutex tests are updated accordingly.

In addition, this adds a paragraph to the "Known issues" section of the
printers README explaining that the printer output isn't guaranteed to cover
every detail.

2017-01-14  Martin Galvan  <martingalvan@sourceware.org>

        * README.pretty-printers (Known issues): Warn about printers not
        always covering everything.
        * nptl/nptl-printers.py (MutexPrinter): Change output.
        * nptl/test-mutex-printers.py: Fix test and adapt to changed output.

ChangeLog

@@ -1,3 +1,10 @@
+2017-01-14  Martin Galvan  <martingalvan@sourceware.org>
+
+	* README.pretty-printers (Known issues): Warn about printers not
+	always covering everything.
+	* nptl/nptl-printers.py (MutexPrinter): Change output.
+	* nptl/test-mutex-printers.py: Fix test and adapt to changed output.
+
 2017-01-20  Stefan Liebler  <stli@linux.vnet.ibm.com>
 
 	* sysdeps/unix/sysv/linux/s390/htm.h: Adjust comments.

README.pretty-printers

@@ -29,7 +29,7 @@ However, with a pretty printer gdb will output something like this:
 (gdb) print mutex
 $1 = pthread_mutex_t = {
   Type = Normal,
-  Status = Unlocked,
+  Status = Not acquired,
   Robust = No,
   Shared = No,
   Protocol = Priority protect,
@@ -145,6 +145,11 @@ any changes to the target code must also update the corresponding printers.
 On the plus side, the printer code itself may serve as a kind of documentation
 for the target code.
 
+* There's no guarantee that the information the pretty printers provide is
+complete, i.e. some details might be left off.  For example, the pthread_mutex_t
+printers won't report whether a thread is spin-waiting in an attempt to acquire
+the mutex.
+
 * Older versions of the gdb Python API have a bug where
 gdb.RegexpCollectionPrettyPrinter would not be able to get a value's real type
 if it was typedef'd.  This would cause gdb to ignore the pretty printers for

nptl/nptl-printers.py

@@ -101,9 +101,9 @@ class MutexPrinter(object):
     def read_status(self):
         """Read the mutex's status.
 
-        For architectures which support lock elision, this method reads
+        Architectures that support lock elision might not record the mutex owner
-        whether the mutex appears as locked in memory (i.e. it may show it as
+        ID in the __owner field.  In that case, the owner will be reported as
-        unlocked even after calling pthread_mutex_lock).
+        "Unknown".
         """
 
         if self.kind == PTHREAD_MUTEX_DESTROYED:
@@ -124,13 +124,14 @@ class MutexPrinter(object):
         """
 
         if self.lock == PTHREAD_MUTEX_UNLOCKED:
-            self.values.append(('Status', 'Unlocked'))
+            self.values.append(('Status', 'Not acquired'))
         else:
             if self.lock & FUTEX_WAITERS:
-                self.values.append(('Status', 'Locked, possibly with waiters'))
+                self.values.append(('Status',
+                                    'Acquired, possibly with waiters'))
             else:
                 self.values.append(('Status',
-                                    'Locked, possibly with no waiters'))
+                                    'Acquired, possibly with no waiters'))
 
             if self.lock & FUTEX_OWNER_DIED:
                 self.values.append(('Owner ID', '%d (dead)' % self.owner))
@@ -147,7 +148,7 @@ class MutexPrinter(object):
     def read_status_no_robust(self):
         """Read the status of a non-robust mutex.
 
-        Read info on whether the mutex is locked, if it may have waiters
+        Read info on whether the mutex is acquired, if it may have waiters
         and its owner (if any).
         """
 
@@ -157,7 +158,7 @@ class MutexPrinter(object):
             lock_value &= ~(PTHREAD_MUTEX_PRIO_CEILING_MASK)
 
         if lock_value == PTHREAD_MUTEX_UNLOCKED:
-            self.values.append(('Status', 'Unlocked'))
+            self.values.append(('Status', 'Not acquired'))
         else:
             if self.kind & PTHREAD_MUTEX_PRIO_INHERIT_NP:
                 waiters = self.lock & FUTEX_WAITERS
@@ -168,12 +169,18 @@ class MutexPrinter(object):
                 owner = self.owner
 
             if waiters:
-                self.values.append(('Status', 'Locked, possibly with waiters'))
+                self.values.append(('Status',
+                                    'Acquired, possibly with waiters'))
             else:
                 self.values.append(('Status',
-                                    'Locked, possibly with no waiters'))
+                                    'Acquired, possibly with no waiters'))
 
+            if self.owner != 0:
                 self.values.append(('Owner ID', owner))
+            else:
+                # Owner isn't recorded, probably because lock elision
+                # is enabled.
+                self.values.append(('Owner ID', 'Unknown'))
 
     def read_attributes(self):
         """Read the mutex's attributes."""
@@ -208,14 +215,14 @@ class MutexPrinter(object):
     def read_misc_info(self):
         """Read miscellaneous info on the mutex.
 
-        For now this reads the number of times a recursive mutex was locked
+        For now this reads the number of times a recursive mutex was acquired
         by the same thread.
         """
 
         mutex_type = self.kind & PTHREAD_MUTEX_KIND_MASK
 
         if mutex_type == PTHREAD_MUTEX_RECURSIVE and self.count > 1:
-            self.values.append(('Times locked recursively', self.count))
+            self.values.append(('Times acquired by the owner', self.count))
 
 class MutexAttributesPrinter(object):
     """Pretty printer for pthread_mutexattr_t.

nptl/test-mutex-printers.py

@@ -39,15 +39,18 @@ try:
 
     break_at(test_source, 'Test status (non-robust)')
     continue_cmd() # Go to test_status_no_robust
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})
     next_cmd()
     thread_id = get_current_thread_lwpid()
-    test_printer(var, to_string, {'Status': 'Locked, possibly with no waiters',
+    # Owner ID might be reported either as the thread ID or as "Unknown"
-                                  'Owner ID': thread_id})
+    # (if e.g. lock elision is enabled).
+    test_printer(var, to_string,
+                 {'Status': 'Acquired, possibly with no waiters',
+                  'Owner ID': r'({0}|Unknown)'.format(thread_id)})
 
     break_at(test_source, 'Test status (robust)')
     continue_cmd() # Go to test_status_robust
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})
 
     # We'll now test the robust mutex locking states.  We'll create a new
     # thread that will lock a robust mutex and exit without unlocking it.
@@ -75,15 +78,15 @@ try:
     test_printer(var, to_string, {'Owner ID': thread_id,
                            'State protected by this mutex': 'Inconsistent'})
     next_cmd()
-    test_printer(var, to_string, {'Status': 'Unlocked',
+    test_printer(var, to_string, {'Status': 'Not acquired',
                         'State protected by this mutex': 'Not recoverable'})
     set_scheduler_locking(False)
 
     break_at(test_source, 'Test recursive locks')
     continue_cmd() # Go to test_recursive_locks
-    test_printer(var, to_string, {'Times locked recursively': '2'})
+    test_printer(var, to_string, {'Times acquired by the owner': '2'})
     next_cmd()
-    test_printer(var, to_string, {'Times locked recursively': '3'})
+    test_printer(var, to_string, {'Times acquired by the owner': '3'})
     continue_cmd() # Exit
 
 except (NoLineError, pexpect.TIMEOUT) as exception: