11507: Cleanup
[arvados.git] / sdk / python / arvados / keep.py
index ec9f6f6422e4736133ada98e971213da6c014e9b..5b4770c4d0dca8824c268448296d0658c8ba04d8 100644 (file)
@@ -1,4 +1,5 @@
 import cStringIO
+import collections
 import datetime
 import hashlib
 import logging
@@ -9,8 +10,10 @@ import Queue
 import re
 import socket
 import ssl
+import sys
 import threading
 import timer
+import urlparse
 
 import arvados
 import arvados.config as config
@@ -22,6 +25,17 @@ _logger = logging.getLogger('arvados.keep')
 global_client_object = None
 
 
+# Monkey patch TCP constants when not available (apple). Values sourced from:
+# http://www.opensource.apple.com/source/xnu/xnu-2422.115.4/bsd/netinet/tcp.h
+if sys.platform == 'darwin':
+    if not hasattr(socket, 'TCP_KEEPALIVE'):
+        socket.TCP_KEEPALIVE = 0x010
+    if not hasattr(socket, 'TCP_KEEPINTVL'):
+        socket.TCP_KEEPINTVL = 0x101
+    if not hasattr(socket, 'TCP_KEEPCNT'):
+        socket.TCP_KEEPCNT = 0x102
+
+
 class KeepLocator(object):
     EPOCH_DATETIME = datetime.datetime.utcfromtimestamp(0)
     HINT_RE = re.compile(r'^[A-Z][A-Za-z0-9@_-]+$')
@@ -148,6 +162,8 @@ class KeepBlockCache(object):
         self._cache_lock = threading.Lock()
 
     class CacheSlot(object):
+        __slots__ = ("locator", "ready", "content")
+
         def __init__(self, locator):
             self.locator = locator
             self.ready = threading.Event()
@@ -210,85 +226,30 @@ class KeepBlockCache(object):
                 self._cache.insert(0, n)
                 return n, True
 
-class KeepClient(object):
-
-    # Default Keep server connection timeout:  2 seconds
-    # Default Keep server read timeout:      300 seconds
-    # Default Keep proxy connection timeout:  20 seconds
-    # Default Keep proxy read timeout:       300 seconds
-    DEFAULT_TIMEOUT = (2, 300)
-    DEFAULT_PROXY_TIMEOUT = (20, 300)
+class Counter(object):
+    def __init__(self, v=0):
+        self._lk = threading.Lock()
+        self._val = v
 
-    class ThreadLimiter(object):
-        """Limit the number of threads writing to Keep at once.
+    def add(self, v):
+        with self._lk:
+            self._val += v
 
-        This ensures that only a number of writer threads that could
-        potentially achieve the desired replication level run at once.
-        Once the desired replication level is achieved, queued threads
-        are instructed not to run.
+    def get(self):
+        with self._lk:
+            return self._val
 
-        Should be used in a "with" block.
-        """
-        def __init__(self, want_copies, max_service_replicas):
-            self._started = 0
-            self._want_copies = want_copies
-            self._done = 0
-            self._response = None
-            self._start_lock = threading.Condition()
-            if (not max_service_replicas) or (max_service_replicas >= want_copies):
-                max_threads = 1
-            else:
-                max_threads = math.ceil(float(want_copies) / max_service_replicas)
-            _logger.debug("Limiter max threads is %d", max_threads)
-            self._todo_lock = threading.Semaphore(max_threads)
-            self._done_lock = threading.Lock()
-            self._local = threading.local()
-
-        def __enter__(self):
-            self._start_lock.acquire()
-            if getattr(self._local, 'sequence', None) is not None:
-                # If the calling thread has used set_sequence(N), then
-                # we wait here until N other threads have started.
-                while self._started < self._local.sequence:
-                    self._start_lock.wait()
-            self._todo_lock.acquire()
-            self._started += 1
-            self._start_lock.notifyAll()
-            self._start_lock.release()
-            return self
-
-        def __exit__(self, type, value, traceback):
-            self._todo_lock.release()
-
-        def set_sequence(self, sequence):
-            self._local.sequence = sequence
-
-        def shall_i_proceed(self):
-            """
-            Return true if the current thread should write to Keep.
-            Return false otherwise.
-            """
-            with self._done_lock:
-                return (self._done < self._want_copies)
-
-        def save_response(self, response_body, replicas_stored):
-            """
-            Records a response body (a locator, possibly signed) returned by
-            the Keep server, and the number of replicas it stored.
-            """
-            with self._done_lock:
-                self._done += replicas_stored
-                self._response = response_body
 
-        def response(self):
-            """Return the body from the response to a PUT request."""
-            with self._done_lock:
-                return self._response
+class KeepClient(object):
 
-        def done(self):
-            """Return the total number of replicas successfully stored."""
-            with self._done_lock:
-                return self._done
+    # Default Keep server connection timeout:  2 seconds
+    # Default Keep server read timeout:       256 seconds
+    # Default Keep server bandwidth minimum:  32768 bytes per second
+    # Default Keep proxy connection timeout:  20 seconds
+    # Default Keep proxy read timeout:        256 seconds
+    # Default Keep proxy bandwidth minimum:   32768 bytes per second
+    DEFAULT_TIMEOUT = (2, 256, 32768)
+    DEFAULT_PROXY_TIMEOUT = (20, 256, 32768)
 
 
     class KeepService(object):
@@ -309,7 +270,9 @@ class KeepClient(object):
             arvados.errors.HttpError,
         )
 
-        def __init__(self, root, user_agent_pool=Queue.LifoQueue(), **headers):
+        def __init__(self, root, user_agent_pool=Queue.LifoQueue(),
+                     upload_counter=None,
+                     download_counter=None, **headers):
             self.root = root
             self._user_agent_pool = user_agent_pool
             self._result = {'error': None}
@@ -318,6 +281,8 @@ class KeepClient(object):
             self.get_headers = {'Accept': 'application/octet-stream'}
             self.get_headers.update(headers)
             self.put_headers = headers
+            self.upload_counter = upload_counter
+            self.download_counter = download_counter
 
         def usable(self):
             """Is it worth attempting a request?"""
@@ -332,31 +297,46 @@ class KeepClient(object):
 
         def _get_user_agent(self):
             try:
-                return self._user_agent_pool.get(False)
+                return self._user_agent_pool.get(block=False)
             except Queue.Empty:
                 return pycurl.Curl()
 
         def _put_user_agent(self, ua):
             try:
                 ua.reset()
-                self._user_agent_pool.put(ua, False)
+                self._user_agent_pool.put(ua, block=False)
             except:
                 ua.close()
 
-        @staticmethod
-        def _socket_open(family, socktype, protocol, address=None):
+        def _socket_open(self, *args, **kwargs):
+            if len(args) + len(kwargs) == 2:
+                return self._socket_open_pycurl_7_21_5(*args, **kwargs)
+            else:
+                return self._socket_open_pycurl_7_19_3(*args, **kwargs)
+
+        def _socket_open_pycurl_7_19_3(self, family, socktype, protocol, address=None):
+            return self._socket_open_pycurl_7_21_5(
+                purpose=None,
+                address=collections.namedtuple(
+                    'Address', ['family', 'socktype', 'protocol', 'addr'],
+                )(family, socktype, protocol, address))
+
+        def _socket_open_pycurl_7_21_5(self, purpose, address):
             """Because pycurl doesn't have CURLOPT_TCP_KEEPALIVE"""
-            s = socket.socket(family, socktype, protocol)
+            s = socket.socket(address.family, address.socktype, address.protocol)
             s.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
-            s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 75)
+            # Will throw invalid protocol error on mac. This test prevents that.
+            if hasattr(socket, 'TCP_KEEPIDLE'):
+                s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 75)
             s.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 75)
             return s
 
-        def get(self, locator, timeout=None):
+        def get(self, locator, method="GET", timeout=None):
             # locator is a KeepLocator object.
             url = self.root + str(locator)
-            _logger.debug("Request: GET %s", url)
+            _logger.debug("Request: %s %s", method, url)
             curl = self._get_user_agent()
+            ok = None
             try:
                 with timer.Timer() as t:
                     self._headers = {}
@@ -368,7 +348,10 @@ class KeepClient(object):
                         '{}: {}'.format(k,v) for k,v in self.get_headers.iteritems()])
                     curl.setopt(pycurl.WRITEFUNCTION, response_body.write)
                     curl.setopt(pycurl.HEADERFUNCTION, self._headerfunction)
+                    if method == "HEAD":
+                        curl.setopt(pycurl.NOBODY, True)
                     self._setcurltimeouts(curl, timeout)
+
                     try:
                         curl.perform()
                     except Exception as e:
@@ -379,6 +362,7 @@ class KeepClient(object):
                         'headers': self._headers,
                         'error': False,
                     }
+
                 ok = retry.check_http_response_success(self._result['status_code'])
                 if not ok:
                     self._result['error'] = arvados.errors.HttpError(
@@ -388,7 +372,6 @@ class KeepClient(object):
                 self._result = {
                     'error': e,
                 }
-                ok = False
             self._usable = ok != False
             if self._result.get('status_code', None):
                 # The client worked well enough to get an HTTP status
@@ -403,11 +386,20 @@ class KeepClient(object):
                 _logger.debug("Request fail: GET %s => %s: %s",
                               url, type(self._result['error']), str(self._result['error']))
                 return None
-            _logger.info("%s response: %s bytes in %s msec (%.3f MiB/sec)",
+            if method == "HEAD":
+                _logger.info("HEAD %s: %s bytes",
+                         self._result['status_code'],
+                         self._result.get('content-length'))
+                return True
+
+            _logger.info("GET %s: %s bytes in %s msec (%.3f MiB/sec)",
                          self._result['status_code'],
                          len(self._result['body']),
                          t.msecs,
                          (len(self._result['body'])/(1024.0*1024))/t.secs if t.secs > 0 else 0)
+
+            if self.download_counter:
+                self.download_counter.add(len(self._result['body']))
             resp_md5 = hashlib.md5(self._result['body']).hexdigest()
             if resp_md5 != locator.md5sum:
                 _logger.warning("Checksum fail: md5(%s) = %s",
@@ -421,37 +413,39 @@ class KeepClient(object):
             url = self.root + hash_s
             _logger.debug("Request: PUT %s", url)
             curl = self._get_user_agent()
+            ok = None
             try:
-                self._headers = {}
-                body_reader = cStringIO.StringIO(body)
-                response_body = cStringIO.StringIO()
-                curl.setopt(pycurl.NOSIGNAL, 1)
-                curl.setopt(pycurl.OPENSOCKETFUNCTION, self._socket_open)
-                curl.setopt(pycurl.URL, url.encode('utf-8'))
-                # Using UPLOAD tells cURL to wait for a "go ahead" from the
-                # Keep server (in the form of a HTTP/1.1 "100 Continue"
-                # response) instead of sending the request body immediately.
-                # This allows the server to reject the request if the request
-                # is invalid or the server is read-only, without waiting for
-                # the client to send the entire block.
-                curl.setopt(pycurl.UPLOAD, True)
-                curl.setopt(pycurl.INFILESIZE, len(body))
-                curl.setopt(pycurl.READFUNCTION, body_reader.read)
-                curl.setopt(pycurl.HTTPHEADER, [
-                    '{}: {}'.format(k,v) for k,v in self.put_headers.iteritems()])
-                curl.setopt(pycurl.WRITEFUNCTION, response_body.write)
-                curl.setopt(pycurl.HEADERFUNCTION, self._headerfunction)
-                self._setcurltimeouts(curl, timeout)
-                try:
-                    curl.perform()
-                except Exception as e:
-                    raise arvados.errors.HttpError(0, str(e))
-                self._result = {
-                    'status_code': curl.getinfo(pycurl.RESPONSE_CODE),
-                    'body': response_body.getvalue(),
-                    'headers': self._headers,
-                    'error': False,
-                }
+                with timer.Timer() as t:
+                    self._headers = {}
+                    body_reader = cStringIO.StringIO(body)
+                    response_body = cStringIO.StringIO()
+                    curl.setopt(pycurl.NOSIGNAL, 1)
+                    curl.setopt(pycurl.OPENSOCKETFUNCTION, self._socket_open)
+                    curl.setopt(pycurl.URL, url.encode('utf-8'))
+                    # Using UPLOAD tells cURL to wait for a "go ahead" from the
+                    # Keep server (in the form of a HTTP/1.1 "100 Continue"
+                    # response) instead of sending the request body immediately.
+                    # This allows the server to reject the request if the request
+                    # is invalid or the server is read-only, without waiting for
+                    # the client to send the entire block.
+                    curl.setopt(pycurl.UPLOAD, True)
+                    curl.setopt(pycurl.INFILESIZE, len(body))
+                    curl.setopt(pycurl.READFUNCTION, body_reader.read)
+                    curl.setopt(pycurl.HTTPHEADER, [
+                        '{}: {}'.format(k,v) for k,v in self.put_headers.iteritems()])
+                    curl.setopt(pycurl.WRITEFUNCTION, response_body.write)
+                    curl.setopt(pycurl.HEADERFUNCTION, self._headerfunction)
+                    self._setcurltimeouts(curl, timeout)
+                    try:
+                        curl.perform()
+                    except Exception as e:
+                        raise arvados.errors.HttpError(0, str(e))
+                    self._result = {
+                        'status_code': curl.getinfo(pycurl.RESPONSE_CODE),
+                        'body': response_body.getvalue(),
+                        'headers': self._headers,
+                        'error': False,
+                    }
                 ok = retry.check_http_response_success(self._result['status_code'])
                 if not ok:
                     self._result['error'] = arvados.errors.HttpError(
@@ -461,7 +455,6 @@ class KeepClient(object):
                 self._result = {
                     'error': e,
                 }
-                ok = False
             self._usable = ok != False # still usable if ok is True or None
             if self._result.get('status_code', None):
                 # Client is functional. See comment in get().
@@ -472,17 +465,30 @@ class KeepClient(object):
                 _logger.debug("Request fail: PUT %s => %s: %s",
                               url, type(self._result['error']), str(self._result['error']))
                 return False
+            _logger.info("PUT %s: %s bytes in %s msec (%.3f MiB/sec)",
+                         self._result['status_code'],
+                         len(body),
+                         t.msecs,
+                         (len(body)/(1024.0*1024))/t.secs if t.secs > 0 else 0)
+            if self.upload_counter:
+                self.upload_counter.add(len(body))
             return True
 
         def _setcurltimeouts(self, curl, timeouts):
             if not timeouts:
                 return
             elif isinstance(timeouts, tuple):
-                conn_t, xfer_t = timeouts
+                if len(timeouts) == 2:
+                    conn_t, xfer_t = timeouts
+                    bandwidth_bps = KeepClient.DEFAULT_TIMEOUT[2]
+                else:
+                    conn_t, xfer_t, bandwidth_bps = timeouts
             else:
                 conn_t, xfer_t = (timeouts, timeouts)
+                bandwidth_bps = KeepClient.DEFAULT_TIMEOUT[2]
             curl.setopt(pycurl.CONNECTTIMEOUT_MS, int(conn_t*1000))
-            curl.setopt(pycurl.TIMEOUT_MS, int(xfer_t*1000))
+            curl.setopt(pycurl.LOW_SPEED_TIME, int(math.ceil(xfer_t)))
+            curl.setopt(pycurl.LOW_SPEED_LIMIT, int(math.ceil(bandwidth_bps)))
 
         def _headerfunction(self, header_line):
             header_line = header_line.decode('iso-8859-1')
@@ -502,68 +508,150 @@ class KeepClient(object):
             self._lastheadername = name
             self._headers[name] = value
             # Returning None implies all bytes were written
-
-
+    
+
+    class KeepWriterQueue(Queue.Queue):
+        def __init__(self, copies):
+            Queue.Queue.__init__(self) # Old-style superclass
+            self.wanted_copies = copies
+            self.successful_copies = 0
+            self.response = None
+            self.successful_copies_lock = threading.Lock()
+            self.pending_tries = copies
+            self.pending_tries_notification = threading.Condition()
+        
+        def write_success(self, response, replicas_nr):
+            with self.successful_copies_lock:
+                self.successful_copies += replicas_nr
+                self.response = response
+            with self.pending_tries_notification:
+                self.pending_tries_notification.notify_all()
+        
+        def write_fail(self, ks):
+            with self.pending_tries_notification:
+                self.pending_tries += 1
+                self.pending_tries_notification.notify()
+        
+        def pending_copies(self):
+            with self.successful_copies_lock:
+                return self.wanted_copies - self.successful_copies
+
+        def get_next_task(self):
+            with self.pending_tries_notification:
+                while True:
+                    if self.pending_copies() < 1:
+                        # This notify_all() is unnecessary --
+                        # write_success() already called notify_all()
+                        # when pending<1 became true, so it's not
+                        # possible for any other thread to be in
+                        # wait() now -- but it's cheap insurance
+                        # against deadlock so we do it anyway:
+                        self.pending_tries_notification.notify_all()
+                        # Drain the queue and then raise Queue.Empty
+                        while True:
+                            self.get_nowait()
+                            self.task_done()
+                    elif self.pending_tries > 0:
+                        service, service_root = self.get_nowait()
+                        if service.finished():
+                            self.task_done()
+                            continue
+                        self.pending_tries -= 1
+                        return service, service_root
+                    elif self.empty():
+                        self.pending_tries_notification.notify_all()
+                        raise Queue.Empty
+                    else:
+                        self.pending_tries_notification.wait()
+
+
+    class KeepWriterThreadPool(object):
+        def __init__(self, data, data_hash, copies, max_service_replicas, timeout=None):
+            self.total_task_nr = 0
+            self.wanted_copies = copies
+            if (not max_service_replicas) or (max_service_replicas >= copies):
+                num_threads = 1
+            else:
+                num_threads = int(math.ceil(float(copies) / max_service_replicas))
+            _logger.debug("Pool max threads is %d", num_threads)
+            self.workers = []
+            self.queue = KeepClient.KeepWriterQueue(copies)
+            # Create workers
+            for _ in range(num_threads):
+                w = KeepClient.KeepWriterThread(self.queue, data, data_hash, timeout)
+                self.workers.append(w)
+        
+        def add_task(self, ks, service_root):
+            self.queue.put((ks, service_root))
+            self.total_task_nr += 1
+        
+        def done(self):
+            return self.queue.successful_copies
+        
+        def join(self):
+            # Start workers
+            for worker in self.workers:
+                worker.start()
+            # Wait for finished work
+            self.queue.join()
+        
+        def response(self):
+            return self.queue.response
+    
+    
     class KeepWriterThread(threading.Thread):
-        """
-        Write a blob of data to the given Keep server. On success, call
-        save_response() of the given ThreadLimiter to save the returned
-        locator.
-        """
-        def __init__(self, keep_service, **kwargs):
-            super(KeepClient.KeepWriterThread, self).__init__()
-            self.service = keep_service
-            self.args = kwargs
-            self._success = False
+        TaskFailed = RuntimeError()
 
-        def success(self):
-            return self._success
+        def __init__(self, queue, data, data_hash, timeout=None):
+            super(KeepClient.KeepWriterThread, self).__init__()
+            self.timeout = timeout
+            self.queue = queue
+            self.data = data
+            self.data_hash = data_hash
+            self.daemon = True
 
         def run(self):
-            limiter = self.args['thread_limiter']
-            sequence = self.args['thread_sequence']
-            if sequence is not None:
-                limiter.set_sequence(sequence)
-            with limiter:
-                if not limiter.shall_i_proceed():
-                    # My turn arrived, but the job has been done without
-                    # me.
+            while True:
+                try:
+                    service, service_root = self.queue.get_next_task()
+                except Queue.Empty:
                     return
-                self.run_with_limiter(limiter)
-
-        def run_with_limiter(self, limiter):
-            if self.service.finished():
-                return
-            _logger.debug("KeepWriterThread %s proceeding %s+%i %s",
-                          str(threading.current_thread()),
-                          self.args['data_hash'],
-                          len(self.args['data']),
-                          self.args['service_root'])
-            self._success = bool(self.service.put(
-                self.args['data_hash'],
-                self.args['data'],
-                timeout=self.args.get('timeout', None)))
-            result = self.service.last_result()
-            if self._success:
-                _logger.debug("KeepWriterThread %s succeeded %s+%i %s",
-                              str(threading.current_thread()),
-                              self.args['data_hash'],
-                              len(self.args['data']),
-                              self.args['service_root'])
-                # Tick the 'done' counter for the number of replica
-                # reported stored by the server, for the case that
-                # we're talking to a proxy or other backend that
-                # stores to multiple copies for us.
                 try:
-                    replicas_stored = int(result['headers']['x-keep-replicas-stored'])
-                except (KeyError, ValueError):
-                    replicas_stored = 1
-                limiter.save_response(result['body'].strip(), replicas_stored)
-            elif result.get('status_code', None):
-                _logger.debug("Request fail: PUT %s => %s %s",
-                              self.args['data_hash'],
-                              result['status_code'],
-                              result['body'])
+                    locator, copies = self.do_task(service, service_root)
+                except Exception as e:
+                    if e is not self.TaskFailed:
+                        _logger.exception("Exception in KeepWriterThread")
+                    self.queue.write_fail(service)
+                else:
+                    self.queue.write_success(locator, copies)
+                finally:
+                    self.queue.task_done()
+
+        def do_task(self, service, service_root):
+            success = bool(service.put(self.data_hash,
+                                        self.data,
+                                        timeout=self.timeout))
+            result = service.last_result()
+
+            if not success:
+                if result.get('status_code', None):
+                    _logger.debug("Request fail: PUT %s => %s %s",
+                                  self.data_hash,
+                                  result['status_code'],
+                                  result['body'])
+                raise self.TaskFailed
+
+            _logger.debug("KeepWriterThread %s succeeded %s+%i %s",
+                          str(threading.current_thread()),
+                          self.data_hash,
+                          len(self.data),
+                          service_root)
+            try:
+                replicas_stored = int(result['headers']['x-keep-replicas-stored'])
+            except (KeyError, ValueError):
+                replicas_stored = 1
+
+            return result['body'].strip(), replicas_stored
 
 
     def __init__(self, api_client=None, proxy=None,
@@ -581,25 +669,28 @@ class KeepClient(object):
         :proxy:
           If specified, this KeepClient will send requests to this Keep
           proxy.  Otherwise, KeepClient will fall back to the setting of the
-          ARVADOS_KEEP_PROXY configuration setting.  If you want to ensure
-          KeepClient does not use a proxy, pass in an empty string.
+          ARVADOS_KEEP_SERVICES or ARVADOS_KEEP_PROXY configuration settings.
+          If you want to KeepClient does not use a proxy, pass in an empty
+          string.
 
         :timeout:
           The initial timeout (in seconds) for HTTP requests to Keep
-          non-proxy servers.  A tuple of two floats is interpreted as
-          (connection_timeout, read_timeout): see
-          http://docs.python-requests.org/en/latest/user/advanced/#timeouts.
-          Because timeouts are often a result of transient server load, the
-          actual connection timeout will be increased by a factor of two on
-          each retry.
-          Default: (2, 300).
+          non-proxy servers.  A tuple of three floats is interpreted as
+          (connection_timeout, read_timeout, minimum_bandwidth). A connection
+          will be aborted if the average traffic rate falls below
+          minimum_bandwidth bytes per second over an interval of read_timeout
+          seconds. Because timeouts are often a result of transient server
+          load, the actual connection timeout will be increased by a factor
+          of two on each retry.
+          Default: (2, 256, 32768).
 
         :proxy_timeout:
           The initial timeout (in seconds) for HTTP requests to
-          Keep proxies. A tuple of two floats is interpreted as
-          (connection_timeout, read_timeout). The behavior described
-          above for adjusting connection timeouts on retry also applies.
-          Default: (20, 300).
+          Keep proxies. A tuple of three floats is interpreted as
+          (connection_timeout, read_timeout, minimum_bandwidth). The behavior
+          described above for adjusting connection timeouts on retry also
+          applies.
+          Default: (20, 256, 32768).
 
         :api_token:
           If you're not using an API client, but only talking
@@ -623,7 +714,10 @@ class KeepClient(object):
         """
         self.lock = threading.Lock()
         if proxy is None:
-            proxy = config.get('ARVADOS_KEEP_PROXY')
+            if config.get('ARVADOS_KEEP_SERVICES'):
+                proxy = config.get('ARVADOS_KEEP_SERVICES')
+            else:
+                proxy = config.get('ARVADOS_KEEP_PROXY')
         if api_token is None:
             if api_client is None:
                 api_token = config.get('ARVADOS_API_TOKEN')
@@ -639,6 +733,12 @@ class KeepClient(object):
         self.timeout = timeout
         self.proxy_timeout = proxy_timeout
         self._user_agent_pool = Queue.LifoQueue()
+        self.upload_counter = Counter()
+        self.download_counter = Counter()
+        self.put_counter = Counter()
+        self.get_counter = Counter()
+        self.hits_counter = Counter()
+        self.misses_counter = Counter()
 
         if local_store:
             self.local_store = local_store
@@ -648,15 +748,21 @@ class KeepClient(object):
             self.num_retries = num_retries
             self.max_replicas_per_service = None
             if proxy:
-                if not proxy.endswith('/'):
-                    proxy += '/'
+                proxy_uris = proxy.split()
+                for i in range(len(proxy_uris)):
+                    if not proxy_uris[i].endswith('/'):
+                        proxy_uris[i] += '/'
+                    # URL validation
+                    url = urlparse.urlparse(proxy_uris[i])
+                    if not (url.scheme and url.netloc):
+                        raise arvados.errors.ArgumentError("Invalid proxy URI: {}".format(proxy_uris[i]))
                 self.api_token = api_token
                 self._gateway_services = {}
                 self._keep_services = [{
-                    'uuid': 'proxy',
+                    'uuid': "00000-bi6l4-%015d" % idx,
                     'service_type': 'proxy',
-                    '_service_root': proxy,
-                    }]
+                    '_service_root': uri,
+                    } for idx, uri in enumerate(proxy_uris)]
                 self._writable_services = self._keep_services
                 self.using_proxy = True
                 self._static_services_list = True
@@ -686,8 +792,10 @@ class KeepClient(object):
         # TODO(twp): the timeout should be a property of a
         # KeepService, not a KeepClient. See #4488.
         t = self.proxy_timeout if self.using_proxy else self.timeout
-        return (t[0] * (1 << attempt_number), t[1])
-
+        if len(t) == 2:
+            return (t[0] * (1 << attempt_number), t[1])
+        else:
+            return (t[0] * (1 << attempt_number), t[1], t[2])
     def _any_nondisk_services(self, service_list):
         return any(ks.get('service_type', 'disk') != 'disk'
                    for ks in service_list)
@@ -790,7 +898,10 @@ class KeepClient(object):
         for root in local_roots:
             if root not in roots_map:
                 roots_map[root] = self.KeepService(
-                    root, self._user_agent_pool, **headers)
+                    root, self._user_agent_pool,
+                    upload_counter=self.upload_counter,
+                    download_counter=self.download_counter,
+                    **headers)
         return local_roots
 
     @staticmethod
@@ -819,8 +930,15 @@ class KeepClient(object):
         else:
             return None
 
+    @retry.retry_method
+    def head(self, loc_s, num_retries=None):
+        return self._get_or_head(loc_s, method="HEAD", num_retries=num_retries)
+
     @retry.retry_method
     def get(self, loc_s, num_retries=None):
+        return self._get_or_head(loc_s, method="GET", num_retries=num_retries)
+
+    def _get_or_head(self, loc_s, method="GET", num_retries=None):
         """Get data from Keep.
 
         This method fetches one or more blocks of data from Keep.  It
@@ -842,11 +960,18 @@ class KeepClient(object):
         """
         if ',' in loc_s:
             return ''.join(self.get(x) for x in loc_s.split(','))
+
+        self.get_counter.add(1)
+
         locator = KeepLocator(loc_s)
-        slot, first = self.block_cache.reserve_cache(locator.md5sum)
-        if not first:
-            v = slot.get()
-            return v
+        if method == "GET":
+            slot, first = self.block_cache.reserve_cache(locator.md5sum)
+            if not first:
+                self.hits_counter.add(1)
+                v = slot.get()
+                return v
+
+        self.misses_counter.add(1)
 
         # If the locator has hints specifying a prefix (indicating a
         # remote keepproxy) or the UUID of a local gateway service,
@@ -862,7 +987,9 @@ class KeepClient(object):
                                    )])
         # Map root URLs to their KeepService objects.
         roots_map = {
-            root: self.KeepService(root, self._user_agent_pool)
+            root: self.KeepService(root, self._user_agent_pool,
+                                   upload_counter=self.upload_counter,
+                                   download_counter=self.download_counter)
             for root in hint_roots
         }
 
@@ -892,16 +1019,20 @@ class KeepClient(object):
                                for root in sorted_roots
                                if roots_map[root].usable()]
             for keep_service in services_to_try:
-                blob = keep_service.get(locator, timeout=self.current_timeout(num_retries-tries_left))
+                blob = keep_service.get(locator, method=method, timeout=self.current_timeout(num_retries-tries_left))
                 if blob is not None:
                     break
             loop.save_result((blob, len(services_to_try)))
 
         # Always cache the result, then return it if we succeeded.
-        slot.set(blob)
-        self.block_cache.cap_cache()
+        if method == "GET":
+            slot.set(blob)
+            self.block_cache.cap_cache()
         if loop.success():
-            return blob
+            if method == "HEAD":
+                return True
+            else:
+                return blob
 
         # Q: Including 403 is necessary for the Keep tests to continue
         # passing, but maybe they should expect KeepReadError instead?
@@ -945,6 +1076,8 @@ class KeepClient(object):
         elif not isinstance(data, str):
             raise arvados.errors.ArgumentError("Argument 'data' to KeepClient.put is not type 'str'")
 
+        self.put_counter.add(1)
+
         data_hash = hashlib.md5(data).hexdigest()
         loc_s = data_hash + '+' + str(len(data))
         if copies < 1:
@@ -953,10 +1086,11 @@ class KeepClient(object):
 
         headers = {}
         # Tell the proxy how many copies we want it to store
-        headers['X-Keep-Desired-Replication'] = str(copies)
+        headers['X-Keep-Desired-Replicas'] = str(copies)
         roots_map = {}
         loop = retry.RetryLoop(num_retries, self._check_loop_result,
                                backoff_start=2)
+        done = 0
         for tries_left in loop:
             try:
                 sorted_roots = self.map_new_services(
@@ -966,29 +1100,22 @@ class KeepClient(object):
                 loop.save_result(error)
                 continue
 
-            thread_limiter = KeepClient.ThreadLimiter(
-                copies, self.max_replicas_per_service)
-            threads = []
+            writer_pool = KeepClient.KeepWriterThreadPool(data=data, 
+                                                        data_hash=data_hash,
+                                                        copies=copies - done,
+                                                        max_service_replicas=self.max_replicas_per_service,
+                                                        timeout=self.current_timeout(num_retries - tries_left))
             for service_root, ks in [(root, roots_map[root])
                                      for root in sorted_roots]:
                 if ks.finished():
                     continue
-                t = KeepClient.KeepWriterThread(
-                    ks,
-                    data=data,
-                    data_hash=data_hash,
-                    service_root=service_root,
-                    thread_limiter=thread_limiter,
-                    timeout=self.current_timeout(num_retries-tries_left),
-                    thread_sequence=len(threads))
-                t.start()
-                threads.append(t)
-            for t in threads:
-                t.join()
-            loop.save_result((thread_limiter.done() >= copies, len(threads)))
+                writer_pool.add_task(ks, service_root)
+            writer_pool.join()
+            done += writer_pool.done()
+            loop.save_result((done >= copies, writer_pool.total_task_nr))
 
         if loop.success():
-            return thread_limiter.response()
+            return writer_pool.response()
         if not roots_map:
             raise arvados.errors.KeepWriteError(
                 "failed to write {}: no Keep services available ({})".format(
@@ -999,7 +1126,7 @@ class KeepClient(object):
                               if roots_map[key].last_result()['error'])
             raise arvados.errors.KeepWriteError(
                 "failed to write {} (wanted {} copies but wrote {})".format(
-                    data_hash, copies, thread_limiter.done()), service_errors, label="service")
+                    data_hash, copies, writer_pool.done()), service_errors, label="service")
 
     def local_store_put(self, data, copies=1, num_retries=None):
         """A stub for put().