summaryrefslogtreecommitdiff
path: root/lib/chef/run_lock.rb
blob: 5f9b1ae06f9661f13b5d0f26bbfe978f74930f04 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
#
# Author:: Daniel DeLeo (<dan@chef.io>)
# Copyright:: Copyright 2012-2016, Chef Software Inc.
# License:: Apache License, Version 2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require_relative "mixin/create_path"
require "fcntl"
if Chef::Platform.windows?
  require_relative "win32/mutex"
end
require_relative "config"
require_relative "exceptions"
require "timeout" unless defined?(Timeout)
require_relative "dist"

class Chef

  # == Chef::RunLock
  # Provides an interface for acquiring and releasing a system-wide exclusive
  # lock.
  #
  # Used by Chef::Client to ensure only one instance of chef-client (or solo)
  # is modifying the system at a time.
  class RunLock
    include Chef::Mixin::CreatePath

    attr_reader :runlock
    attr_reader :mutex
    attr_reader :runlock_file

    # Create a new instance of RunLock
    # === Arguments
    # * :lockfile::: the full path to the lockfile.
    def initialize(lockfile)
      @runlock_file = lockfile
      @runlock = nil
      @mutex = nil
      @runpid = nil
    end

    # Acquire the system-wide lock. Will block indefinitely if another process
    # already has the lock and Chef::Config[:run_lock_timeout] is
    # not set. Otherwise will block for Chef::Config[:run_lock_timeout]
    # seconds and exit if the lock is not acquired.
    #
    # Each call to acquire should have a corresponding call to #release.
    #
    # The implementation is based on File#flock (see also: flock(2)).
    #
    # Either acquire() or test() methods should be called in order to
    # get the ownership of run_lock.
    def acquire
      if timeout_given?
        begin
          Timeout.timeout(time_to_wait) do
            unless test
              if time_to_wait > 0.0
                wait
              else
                exit_from_timeout
              end
            end
          end
        rescue Timeout::Error
          exit_from_timeout
        end
      else
        wait unless test
      end
    end

    #
    # Tests and if successful acquires the system-wide lock.
    # Returns true if the lock is acquired, false otherwise.
    #
    # Either acquire() or test() methods should be called in order to
    # get the ownership of run_lock.
    def test
      create_lock
      acquire_lock
    end

    #
    # Waits until acquiring the system-wide lock.
    #
    def wait
      Chef::Log.warn("#{Chef::Dist::PRODUCT} #{runpid} is running, will wait for it to finish and then run.")
      if Chef::Platform.windows?
        mutex.wait
      else
        runlock.flock(File::LOCK_EX)
      end
    end

    def save_pid
      runlock.truncate(0)
      runlock.rewind # truncate doesn't reset position to 0.
      runlock.write(Process.pid.to_s)
      # flush the file fsync flushes the system buffers
      # in addition to ruby buffers
      runlock.fsync
    end

    # Release the system-wide lock.
    def release
      if runlock
        if Chef::Platform.windows?
          mutex.release
        else
          runlock.flock(File::LOCK_UN)
        end
        runlock.close
        # Don't unlink the pid file, if another chef-client was waiting, it
        # won't be recreated. Better to leave a "dead" pid file than not have
        # it available if you need to break the lock.
        reset
      end
    end

    # @api private solely for race condition tests
    def create_lock
      # ensure the runlock_file path exists
      create_path(File.dirname(runlock_file))
      @runlock = File.open(runlock_file, "a+")
    end

    # @api private solely for race condition tests
    def acquire_lock
      if Chef::Platform.windows?
        acquire_win32_mutex
      else
        # If we support FD_CLOEXEC, then use it.
        # NB: ruby-2.0.0-p195 sets FD_CLOEXEC by default, but not
        # ruby-1.8.7/1.9.3
        if Fcntl.const_defined?("F_SETFD") && Fcntl.const_defined?("FD_CLOEXEC")
          runlock.fcntl(Fcntl::F_SETFD, runlock.fcntl(Fcntl::F_GETFD, 0) | Fcntl::FD_CLOEXEC)
        end
        # Flock will return 0 if it can acquire the lock otherwise it
        # will return false
        if runlock.flock(File::LOCK_NB | File::LOCK_EX) == 0
          true
        else
          false
        end
      end
    end

    private

    def reset
      @runlock = nil
      @mutex = nil
      @runpid = nil
    end

    # Since flock mechanism doesn't exist on windows we are using
    # platform Mutex.
    # We are creating a "Global" mutex here so that non-admin
    # users can not DoS chef-client by creating the same named
    # mutex we are using locally.
    # Mutex name is case-sensitive contrary to other things in
    # windows. "\" is the only invalid character.
    def acquire_win32_mutex
      @mutex = Chef::ReservedNames::Win32::Mutex.new("Global\\#{runlock_file.gsub(/[\\]/, "/").downcase}")
      mutex.test
    end

    def runpid
      @runpid ||= runlock.read.strip
    end

    def timeout_given?
      !time_to_wait.nil?
    end

    def time_to_wait
      Chef::Config[:run_lock_timeout]
    end

    def exit_from_timeout
      rp = runpid
      release # Just to be on the safe side...
      raise Chef::Exceptions::RunLockTimeout.new(time_to_wait, rp)
    end
  end
end