From d65979cc2e49bd4fde5fc97b787e56aaf82ce2eb Mon Sep 17 00:00:00 2001
From: Patrick Mahoney <pat@polycrystal.org>
Date: Sat, 17 Dec 2011 11:05:39 -0600
Subject: [PATCH] Initial attempt at ConditionVariable implementation.

---
 lib/process_shared/condition_variable.rb      | 38 +++++++++--
 .../process_shared/condition_variable_spec.rb | 67 +++++++++++++++++++
 2 files changed, 101 insertions(+), 4 deletions(-)
 create mode 100644 spec/process_shared/condition_variable_spec.rb

diff --git a/lib/process_shared/condition_variable.rb b/lib/process_shared/condition_variable.rb
index afca674..4348d1d 100644
--- a/lib/process_shared/condition_variable.rb
+++ b/lib/process_shared/condition_variable.rb
@@ -1,14 +1,16 @@
 require 'process_shared/semaphore'
 
 module ProcessShared
-  # TODO: implement this
   class ConditionVariable
     def initialize
-      @sem = Semaphore.new
+      @internal = Semaphore.new(1)
+      @waiting = SharedMemory.new(:int)
+      @waiting.write_int(0)
+      @sem = Semaphore.new(0)
     end
 
     def broadcast
-      @sem.post
+      waiting.times { @sem.post }
     end
 
     def signal
@@ -18,10 +20,38 @@ module ProcessShared
     def wait(mutex, timeout = nil)
       mutex.unlock
       begin
-        @sem.wait
+        inc_waiting
+        if timeout
+          begin
+            @sem.try_wait(timeout)
+          rescue Errno::EAGAIN, Errno::ETIMEDOUT
+            # success!
+          end
+        else
+          @sem.wait
+        end
+        dec_waiting
       ensure
         mutex.lock
       end
     end
+
+    private
+
+    def waiting
+      @internal.synchronize do
+        @waiting.read_int
+      end
+    end
+
+    def inc_waiting(val = 1)
+      @internal.synchronize do
+        @waiting.write_int(@waiting.read_int + val)
+      end
+    end
+
+    def dec_waiting
+      inc_waiting(-1)
+    end
   end
 end
diff --git a/spec/process_shared/condition_variable_spec.rb b/spec/process_shared/condition_variable_spec.rb
new file mode 100644
index 0000000..7ffcaba
--- /dev/null
+++ b/spec/process_shared/condition_variable_spec.rb
@@ -0,0 +1,67 @@
+require 'spec_helper'
+
+require 'process_shared/condition_variable'
+
+module ProcessShared
+  describe ConditionVariable do
+    it 'runs the example of Ruby Stdlib ConditionVariable' do
+      mutex = Mutex.new
+      resource = ConditionVariable.new
+
+      a = fork {
+        mutex.synchronize {
+          resource.wait(mutex)
+        }
+        Kernel.exit!
+      }
+      
+      b = fork {
+        mutex.synchronize {
+          resource.signal
+        }
+        Kernel.exit!
+      }
+
+      ::Process.wait(a)
+      ::Process.wait(b)
+    end
+
+    it 'broadcasts to multiple processes' do
+      mutex = Mutex.new
+      cond = ConditionVariable.new
+      mem = SharedMemory.new(:int)
+      mem.write_int(0)
+
+      pids = []
+      10.times do
+        pids << fork do
+          mutex.synchronize {
+            cond.wait(mutex)
+            mem.write_int(mem.read_int + 1)
+          }
+          Kernel.exit!
+        end
+      end
+
+      sleep 0.2               # hopefully they are all waiting...
+      mutex.synchronize {
+        cond.broadcast
+      }
+
+      pids.each { |p| ::Process.wait(p) }
+
+      mem.read_int.must_equal(10)
+    end
+
+    it 'stops waiting after timeout' do
+      mutex = Mutex.new
+      cond = ConditionVariable.new
+
+      mutex.synchronize {
+        start = Time.now.to_f
+        cond.wait(mutex, 0.1)
+        (Time.now.to_f - start).must be_gte(0.1)
+      }
+    end
+  end
+end