[PATCH] Add pretty printers for the NPTL lock types

[Martin Galvan <martin dot galvan at tallertechnologies dot com>]

This patch adds the pretty-printers for the following NPTL types:

- pthread_mutex_t
- pthread_mutexattr_t
- pthread_cond_t
- pthread_condattr_t
- pthread_rwlock_t
- pthread_rwlockattr_t

To load the pretty-printers into your gdb session, do:

source printers.py

You can check which printers are registered and enabled by issuing the
'info pretty-printer' gdb command. Printers should trigger automatically when
trying to print a variable of one of the types mentioned above.

I spent a lot of time trying to change the install target inside the
NPTL Makefile so that the printers would be automatically installed to
$datadir/gdb/auto-load, and properly renamed to libpthread(version)-gdb.py.
Since I didn't succeed you'll have to install them manually; it would be great
if someone who's more familiar with the build system could add it to the Makefile.

These printers are architecture-independent. However, most of the C macros
defined in nptl/pthread.h and nptl/pthreadP.h had to be replicated in the Python
code as global variables as there was no other way to check which flags were
set.

The printers were tested on both the gdb CLI and Eclipse CDT.

I have a company-wide copyright assignment for glibc. I don't have write access,
though, so if anyone could commit this for me it would be great.

ChangeLog:
2015-05-15  Martin Galvan  <martin.galvan@tallertechnologies.com>
	* nptl/printers.py: New file.
---
 nptl/printers.py | 744 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 744 insertions(+)
 create mode 100644 nptl/printers.py

diff --git a/nptl/printers.py b/nptl/printers.py
new file mode 100644
index 0000000..fdab6e8
--- /dev/null
+++ b/nptl/printers.py
@@ -0,0 +1,744 @@
+# Copyright (C) 2015 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+# Contributed by Martin Galvan <martin.galvan@tallertechnologies.com>
+#
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <http://www.gnu.org/licenses/>.
+
+"""Pretty printers for the NTPL lock types.
+
+This file contains the gdb pretty printers for the following types:
+
+    * pthread_mutex_t
+    * pthread_mutexattr_t
+    * pthread_cond_t
+    * pthread_condattr_t
+    * pthread_rwlock_t
+    * pthread_rwlockattr_t
+
+You can check which printers are registered and enabled by issuing the
+'info pretty-printer' gdb command. Printers should trigger automatically when
+trying to print a variable of one of the types mentioned above.
+"""
+
+import sys
+import re
+import ctypes
+import gdb
+
+class _IteratorP3(object):
+    """A simple Iterator class."""
+
+    def __init__(self, values):
+        self.values = values
+        self.length = len(self.values)
+        self.count = 0
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        count = self.count
+        self.count += 1
+
+        if count == self.length:
+            raise StopIteration
+        else:
+            return self.values[count]
+
+class _IteratorP2(_IteratorP3):
+    """Hack for Python 2 compatibilty."""
+
+    def next(self):
+        self.__next__()
+
+# Hack for Python 2 compatibilty
+if sys.version_info[0] > 2:
+    Iterator = _IteratorP3
+else:
+    Iterator = _IteratorP2
+
+################################################################################
+
+# These variables correspond to the macros defined in nptl/pthread.h and
+# nptl/pthreadP.h. Unfortunately, as those values are hardcoded in the glibc
+# code, updating the macros will require updating these variables as well.
+
+# Mutex types
+PTHREAD_MUTEX_KIND_MASK = 0x3
+PTHREAD_MUTEX_NORMAL = 0
+PTHREAD_MUTEX_RECURSIVE = 1
+PTHREAD_MUTEX_ERRORCHECK = 2
+PTHREAD_MUTEX_ADAPTIVE_NP = 3
+
+# Mutex status
+PTHREAD_MUTEX_DESTROYED = -1
+PTHREAD_MUTEX_UNLOCKED = 0
+PTHREAD_MUTEX_LOCKED_NO_WAITERS = 1
+
+# INT_MAX for 2's complement CPUs
+PTHREAD_MUTEX_INCONSISTENT = gdb.parse_and_eval('~0u >> 1')
+PTHREAD_MUTEX_NOTRECOVERABLE = PTHREAD_MUTEX_INCONSISTENT - 1
+
+# For robust mutexes
+FUTEX_OWNER_DIED = 0x40000000
+
+# For robust and PI mutexes
+FUTEX_WAITERS = 0x80000000
+FUTEX_TID_MASK = 0x3FFFFFFF
+
+# Mutex attributes
+PTHREAD_MUTEX_ROBUST_NORMAL_NP = 0x10
+PTHREAD_MUTEX_PRIO_INHERIT_NP = 0x20
+PTHREAD_MUTEX_PRIO_PROTECT_NP = 0x40
+PTHREAD_MUTEX_PSHARED_BIT = 0x80
+PTHREAD_MUTEX_PRIO_CEILING_SHIFT = 19
+PTHREAD_MUTEX_PRIO_CEILING_MASK = 0x7FF80000
+
+mutexTypesDict = {
+    PTHREAD_MUTEX_NORMAL: ('Type', 'Normal'),
+    PTHREAD_MUTEX_RECURSIVE: ('Type', 'Recursive'),
+    PTHREAD_MUTEX_ERRORCHECK: ('Type', 'Error check'),
+    PTHREAD_MUTEX_ADAPTIVE_NP: ('Type', 'Adaptive')
+}
+
+class MutexPrinter(object):
+    """Pretty printer for pthread_mutex_t."""
+
+    def __init__(self, mutex):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            mutex: A gdb.value representing a pthread_mutex_t.
+        """
+
+        data = mutex['__data']
+        self.lock = data['__lock']
+        self.count = data['__count']
+        self.owner = data['__owner']
+        self.kind = data['__kind']
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_mutex_t.
+        """
+
+        return 'pthread_mutex_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_mutex_t.
+        """
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the mutex's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        self.readType()
+        self.readStatus()
+        self.readAttributes()
+        self.readMiscInfo()
+
+    def readType(self):
+        """Read the mutex's type."""
+
+        mutexType = self.kind & PTHREAD_MUTEX_KIND_MASK
+
+        # mutexType must be casted to int because it's a gdb.Value
+        self.values.append(mutexTypesDict[int(mutexType)])
+
+    def readStatus(self):
+        """Read the mutex's status.
+
+        For architectures which support lock elision, this method reads
+        whether the mutex is actually locked (i.e. it may show it as unlocked
+        even after calling pthread_mutex_lock).
+        """
+
+        if self.kind == PTHREAD_MUTEX_DESTROYED:
+            self.values.append(('Status', 'Destroyed'))
+        elif self.kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP:
+            self.readStatusRobust()
+        else:
+            self.readStatusNonRobust()
+
+    def readStatusRobust(self):
+        """Read the status of a robust mutex.
+
+        In glibc robust mutexes are implemented in a very different way than
+        non-robust ones. This method reads their locking status,
+        whether it may have waiters, their registered owner (if any),
+        whether the owner is alive or not, and the status of the state
+        they're protecting.
+        """
+
+        if self.lock == PTHREAD_MUTEX_UNLOCKED:
+            self.values.append(('Status', 'Unlocked'))
+        else:
+            if self.lock & FUTEX_WAITERS:
+                self.values.append(('Status', 'Locked, possibly with waiters'))
+            else:
+                self.values.append(('Status', 'Locked, no waiters'))
+
+            if self.lock & FUTEX_OWNER_DIED:
+                self.values.append(('Owner ID', '%d (dead)' % self.owner))
+            else:
+                self.values.append(('Owner ID', self.lock & FUTEX_TID_MASK))
+
+        if self.owner == PTHREAD_MUTEX_INCONSISTENT:
+            self.values.append(('State protected by this mutex',
+                                'Inconsistent'))
+        elif self.owner == PTHREAD_MUTEX_NOTRECOVERABLE:
+            self.values.append(('State protected by this mutex',
+                                'Not recoverable'))
+
+    def readStatusNonRobust(self):
+        """Read the status of a non-robust mutex.
+
+        Read info on whether the mutex is locked, if it may have waiters
+        and its owner (if any).
+        """
+
+        if self.lock == PTHREAD_MUTEX_UNLOCKED:
+            self.values.append(('Status', 'Unlocked'))
+        else:
+            if self.kind & PTHREAD_MUTEX_PRIO_INHERIT_NP:
+                waiters = self.lock & FUTEX_WAITERS
+                owner = self.lock & FUTEX_TID_MASK
+            else:
+                # Mutex protocol is PP or none
+                waiters = (self.lock != PTHREAD_MUTEX_LOCKED_NO_WAITERS)
+                owner = self.owner
+
+            if waiters:
+                self.values.append(('Status', 'Locked, possibly with waiters'))
+            else:
+                self.values.append(('Status', 'Locked, no waiters'))
+
+            self.values.append(('Owner ID', owner))
+
+    def readAttributes(self):
+        """Read the mutex's attributes."""
+
+        if self.kind != PTHREAD_MUTEX_DESTROYED:
+            if self.kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP:
+                self.values.append(('Robust', 'Yes'))
+            else:
+                self.values.append(('Robust', 'No'))
+
+            # In glibc, robust mutexes always have their pshared flag set to
+            # 'shared' regardless of what the pshared flag of their
+            # mutexattr was. Therefore a robust mutex will act as shared even if
+            # it was initialized with a 'private' mutexattr.
+            if self.kind & PTHREAD_MUTEX_PSHARED_BIT:
+                self.values.append(('Shared', 'Yes'))
+            else:
+                self.values.append(('Shared', 'No'))
+
+            if self.kind & PTHREAD_MUTEX_PRIO_INHERIT_NP:
+                self.values.append(('Protocol', 'Priority inherit'))
+            elif self.kind & PTHREAD_MUTEX_PRIO_PROTECT_NP:
+                prioCeiling = ((self.lock & PTHREAD_MUTEX_PRIO_CEILING_MASK) >>
+                               PTHREAD_MUTEX_PRIO_CEILING_SHIFT)
+
+                self.values.append(('Protocol', 'Priority protect'))
+                self.values.append(('Priority ceiling', prioCeiling))
+            else:
+                # PTHREAD_PRIO_NONE
+                self.values.append(('Protocol', 'None'))
+
+    def readMiscInfo(self):
+        """Read miscellaneous info on the mutex.
+
+        For now this reads the number of times a row a recursive mutex
+        was locked by the same thread.
+        """
+
+        mutexType = self.kind & PTHREAD_MUTEX_KIND_MASK
+
+        if mutexType == PTHREAD_MUTEX_RECURSIVE and self.count > 1:
+            self.values.append(('Times locked recursively', self.count))
+
+################################################################################
+
+# Mutex attribute flags
+PTHREAD_MUTEXATTR_PROTOCOL_SHIFT = 28
+PTHREAD_MUTEXATTR_PROTOCOL_MASK = 0x30000000
+PTHREAD_MUTEXATTR_PRIO_CEILING_MASK = 0x00FFF000
+PTHREAD_MUTEXATTR_FLAG_ROBUST = 0x40000000
+PTHREAD_MUTEXATTR_FLAG_PSHARED = 0x80000000
+
+PTHREAD_MUTEXATTR_FLAG_BITS = (PTHREAD_MUTEXATTR_FLAG_ROBUST |
+                               PTHREAD_MUTEXATTR_FLAG_PSHARED |
+                               PTHREAD_MUTEXATTR_PROTOCOL_MASK |
+                               PTHREAD_MUTEXATTR_PRIO_CEILING_MASK)
+
+PTHREAD_MUTEX_NO_ELISION_NP = 0x200
+
+# Priority protocols
+PTHREAD_PRIO_NONE = 0
+PTHREAD_PRIO_INHERIT = 1
+PTHREAD_PRIO_PROTECT = 2
+
+class MutexAttributesPrinter(object):
+    """Pretty printer for pthread_mutexattr_t.
+
+    In the NPTL this is a type that's always casted to struct pthread_mutexattr,
+    which has a single 'mutexkind' field containing the actual attributes.
+    """
+
+    def __init__(self, mutexattr):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            mutexattr: A gdb.value representing a pthread_mutexattr_t.
+        """
+
+        mutexattrStruct = gdb.lookup_type('struct pthread_mutexattr')
+        self.mutexattr = mutexattr.cast(mutexattrStruct)['mutexkind']
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_mutexattr_t.
+        """
+
+        return 'pthread_mutexattr_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_mutexattr_t.
+        """
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the mutexattr's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        mutexattrType = (self.mutexattr &
+                         ~PTHREAD_MUTEXATTR_FLAG_BITS &
+                         ~PTHREAD_MUTEX_NO_ELISION_NP)
+
+        # mutexattrType must be casted to int because it's a gdb.Value
+        self.values.append(mutexTypesDict[int(mutexattrType)])
+
+        if self.mutexattr & PTHREAD_MUTEXATTR_FLAG_ROBUST:
+            self.values.append(('Robust', 'Yes'))
+        else:
+            self.values.append(('Robust', 'No'))
+
+        if self.mutexattr & PTHREAD_MUTEXATTR_FLAG_PSHARED:
+            self.values.append(('Shared', 'Yes'))
+        else:
+            self.values.append(('Shared', 'No'))
+
+        protocol = ((self.mutexattr & PTHREAD_MUTEXATTR_PROTOCOL_MASK) >>
+                    PTHREAD_MUTEXATTR_PROTOCOL_SHIFT)
+
+        if protocol == PTHREAD_PRIO_NONE:
+            self.values.append(('Protocol', 'None'))
+        elif protocol == PTHREAD_PRIO_INHERIT:
+            self.values.append(('Protocol', 'Priority inherit'))
+        elif protocol == PTHREAD_PRIO_PROTECT:
+            self.values.append(('Protocol', 'Priority protect'))
+
+################################################################################
+
+# Value of __mutex for shared condvars.
+PTHREAD_COND_SHARED = ~ctypes.c_long(0).value
+
+# Value of __total_seq for destroyed condvars.
+PTHREAD_COND_DESTROYED = ctypes.c_ulonglong(-1).value
+
+# __nwaiters encodes the number of threads waiting on a condvar
+# and the clock ID.
+# __nwaiters >> COND_NWAITERS_SHIFT gives us the number of waiters.
+COND_NWAITERS_SHIFT = 1
+
+class ConditionVariablePrinter(object):
+    """Pretty printer for pthread_cond_t."""
+
+    def __init__(self, cond):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            cond: A gdb.value representing a pthread_cond_t.
+        """
+
+        data = cond['__data']
+        self.totalSeq = data['__total_seq']
+        self.mutex = data['__mutex']
+        self.nwaiters = data['__nwaiters']
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_cond_t.
+        """
+
+        return 'pthread_cond_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_cond_t.
+        """
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the condvar's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        self.readStatus()
+        self.readAttributes()
+        self.readMutexInfo()
+
+    def readStatus(self):
+        """Read the status of the condvar.
+
+        This method reads whether the condvar is destroyed and how many threads
+        are waiting for it.
+        """
+
+        if self.totalSeq == PTHREAD_COND_DESTROYED:
+            self.values.append(('Status', 'Destroyed'))
+
+        self.values.append(('Threads waiting for this condvar',
+                           self.nwaiters >> COND_NWAITERS_SHIFT))
+
+    def readAttributes(self):
+        """Read the condvar's attributes."""
+
+        clockID = self.nwaiters & ((1 << COND_NWAITERS_SHIFT) - 1)
+        shared = (self.mutex == PTHREAD_COND_SHARED)
+
+        if shared:
+            self.values.append(('Shared', 'Yes'))
+        else:
+            self.values.append(('Shared', 'No'))
+
+        self.values.append(('Clock ID', clockID))
+
+    def readMutexInfo(self):
+        """Read the data of the mutex this condvar is bound to.
+
+        A pthread_cond_t's __data.__mutex member is a void * which
+        must be casted to pthread_mutex_t *. For shared condvars, this
+        member isn't recorded and has a value of ~0l instead.
+        """
+
+        if self.mutex and self.mutex != PTHREAD_COND_SHARED:
+            mutexType = gdb.lookup_type('pthread_mutex_t')
+            mutex = self.mutex.cast(mutexType.pointer()).dereference()
+
+            self.values.append(('Mutex', mutex))
+
+################################################################################
+
+class ConditionVariableAttributesPrinter(object):
+    """Pretty printer for pthread_condattr_t.
+
+    In the NPTL this is a type that's
+    always casted to struct pthread_condattr, which has a single 'value' field
+    containing the actual attributes.
+    """
+
+    def __init__(self, condattr):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            condattr: A gdb.value representing a pthread_condattr_t.
+        """
+
+        condattrStruct = gdb.lookup_type('struct pthread_condattr')
+        self.condattr = condattr.cast(condattrStruct)['value']
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_condattr_t.
+        """
+
+        return 'pthread_condattr_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_condattr_t.
+        """
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the condattr's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        clockID = self.condattr & ((1 << COND_NWAITERS_SHIFT) - 1)
+
+        if self.condattr & 1:
+            self.values.append(('Shared', 'Yes'))
+        else:
+            self.values.append(('Shared', 'No'))
+
+        self.values.append(('Clock ID', clockID))
+
+################################################################################
+
+class RWLockPrinter(object):
+    """Pretty printer for pthread_rwlock_t."""
+
+    def __init__(self, rwlock):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            rwlock: A gdb.value representing a pthread_rwlock_t.
+        """
+
+        data = rwlock['__data']
+        self.readers = data['__nr_readers']
+        self.queuedReaders = data['__nr_readers_queued']
+        self.queuedWriters = data['__nr_writers_queued']
+        self.writerID = data['__writer']
+        self.shared = data['__shared']
+        self.prefersWriters = data['__flags']
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_rwlock_t.
+        """
+
+        return 'pthread_rwlock_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_rwlock_t.
+        """
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the rwlock's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        self.readStatus()
+        self.readAttributes()
+
+    def readStatus(self):
+        """Read the status of the rwlock."""
+
+        if self.writerID:
+            self.values.append(('Status', 'Locked (Write)'))
+            self.values.append(('Writer ID', self.writerID))
+        elif self.readers:
+            self.values.append(('Status', 'Locked (Read)'))
+            self.values.append(('Readers', self.readers))
+        else:
+            self.values.append(('Status', 'Unlocked'))
+
+        self.values.append(('Queued readers', self.queuedReaders))
+        self.values.append(('Queued writers', self.queuedWriters))
+
+    def readAttributes(self):
+        """Read the attributes of the rwlock."""
+
+        if self.shared:
+            self.values.append(('Shared', 'Yes'))
+        else:
+            self.values.append(('Shared', 'No'))
+
+        if self.prefersWriters:
+            self.values.append(('Prefers', 'Writers'))
+        else:
+            self.values.append(('Prefers', 'Readers'))
+
+################################################################################
+
+# Rwlock attributes
+PTHREAD_RWLOCK_PREFER_READER_NP = 0
+PTHREAD_RWLOCK_PREFER_WRITER_NP = 1
+PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP = 2
+
+# 'Shared' attribute values
+PTHREAD_PROCESS_PRIVATE = 0
+PTHREAD_PROCESS_SHARED = 1
+
+class RWLockAttributesPrinter(object):
+    """Pretty printer for pthread_rwlockattr_t.
+
+    In the NPTL this is a type that's always casted to
+    struct pthread_rwlockattr, which has two fields ('lockkind' and 'pshared')
+    containing the actual attributes.
+    """
+
+    def __init__(self, rwlockattr):
+        """Initialize the printer's internal data structures.
+
+        Args:
+            rwlockattr: A gdb.value representing a pthread_rwlockattr_t.
+        """
+
+        rwlockattrStruct = gdb.lookup_type('struct pthread_rwlockattr')
+        self.rwlockattr = rwlockattr.cast(rwlockattrStruct)
+        self.values = []
+        self.readValues()
+
+    def to_string(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_rwlockattr_t."""
+
+        return 'pthread_rwlockattr_t'
+
+    def children(self):
+        """gdb API function.
+
+        This is called from gdb when we try to print a pthread_rwlockattr_t."""
+
+        return Iterator(self.values)
+
+    def readValues(self):
+        """Read the rwlockattr's info and store it in self.values.
+
+        The data contained in self.values will be returned by the Iterator
+        created in self.children.
+        """
+
+        rwlockType = self.rwlockattr['lockkind']
+        shared = self.rwlockattr['pshared']
+
+        if shared == PTHREAD_PROCESS_SHARED:
+            self.values.append(('Shared', 'Yes'))
+        else:
+            # PTHREAD_PROCESS_PRIVATE
+            self.values.append(('Shared', 'No'))
+
+        if rwlockType == PTHREAD_RWLOCK_PREFER_READER_NP:
+            self.values.append(('Prefers', 'Readers'))
+        elif (rwlockType == PTHREAD_RWLOCK_PREFER_WRITER_NP or
+              rwlockType == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP):
+            self.values.append(('Prefers', 'Writers'))
+
+################################################################################
+
+class Printer(object):
+    """Printer class which conforms to the gdb pretty printing interface."""
+
+    def __init__(self, name):
+        self.name = name
+        self.enabled = True
+        self.subprinters = []
+
+    class Subprinter(object):
+        """A regex-based printer.
+
+        Individual pretty-printers are registered as subprinters of a single
+        Printer instance.
+        """
+
+        def __init__(self, name, regex, callable):
+            """
+            Initialize a pretty-printer.
+
+            Args:
+                name: The name of the printer.
+                regex: A regular expression. When gdb tries to print a variable
+                    whose type matches the regex it'll trigger this printer.
+                callable: A function or callable object that gdb will call
+                    when trying to print some value. It should return a
+                    pretty-printer.
+            """
+            self.name = name
+            self.regex = re.compile(regex)
+            self.callable = callable
+            self.enabled = True
+
+    def addSubprinter(self, name, regex, callable):
+        """Register a regex-based subprinter."""
+
+        self.subprinters.append(self.Subprinter(name, regex, callable))
+
+    def __call__(self, value):
+        """gdb API function.
+
+        This is called when trying to print an inferior value
+        from gdb. If a registered printer's regex matches the value's type,
+        gdb will use the printer to print the value.
+        """
+
+        typeName = value.type.name
+
+        if typeName:
+            for subprinter in self.subprinters:
+                if subprinter.enabled and subprinter.regex.match(typeName):
+                    return subprinter.callable(value)
+
+        # Return None if we have no type name or if we can't find a subprinter
+        # for the given type.
+        return None
+
+################################################################################
+
+def register(objfile):
+    """Register the pretty printers within the given objfile."""
+
+    printer = Printer('Glibc pthread locks')
+
+    printer.addSubprinter('pthread_mutex_t', '^pthread_mutex_t$', MutexPrinter)
+    printer.addSubprinter('pthread_mutexattr_t', '^pthread_mutexattr_t$',
+                          MutexAttributesPrinter)
+    printer.addSubprinter('pthread_cond_t', '^pthread_cond_t$',
+                          ConditionVariablePrinter)
+    printer.addSubprinter('pthread_condattr_t', '^pthread_condattr_t$',
+                          ConditionVariableAttributesPrinter)
+    printer.addSubprinter('pthread_rwlock_t', '^pthread_rwlock_t$', RWLockPrinter)
+    printer.addSubprinter('pthread_rwlockattr_t', '^pthread_rwlockattr_t$',
+                          RWLockAttributesPrinter)
+
+    gdb.printing.register_pretty_printer(objfile, printer)
+
+register(gdb.current_objfile())
-- 
2.4.0