From 8d932577d12c2355fd263ee2dc8cd63593fc9ad8 Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Sun, 14 Oct 2018 15:46:54 +0200
Subject: [PATCH 1/4] Fix: POSIX threads return an errnum, but don't set errno

- Pass the returned errnum to `Errno.new`.

- Fix `Thread::Mutex.try_lock` to return true when the lock was
  acquired and false otherwise.

- Add a spec for `Thread.current`.
---
 spec/std/thread_spec.cr          |  8 ++++++++
 src/gc/boehm.cr                  |  2 +-
 src/thread.cr                    |  6 +++---
 src/thread/condition_variable.cr | 25 ++++++++++---------------
 src/thread/mutex.cr              | 29 +++++++++++++++--------------
 5 files changed, 37 insertions(+), 33 deletions(-)

diff --git a/spec/std/thread_spec.cr b/spec/std/thread_spec.cr
index f16938655c01..47e1db6d6bf3 100644
--- a/spec/std/thread_spec.cr
+++ b/spec/std/thread_spec.cr
@@ -14,4 +14,12 @@ describe Thread do
       thread.join
     end
   end
+
+  it "returns current thread object" do
+    current = nil
+    thread = Thread.new { current = Thread.current }
+    thread.join
+    current.should be(thread)
+    current.should_not be(Thread.current)
+  end
 end
diff --git a/src/gc/boehm.cr b/src/gc/boehm.cr
index bf37a5f607c7..92c4faa5dd70 100644
--- a/src/gc/boehm.cr
+++ b/src/gc/boehm.cr
@@ -162,7 +162,7 @@ module GC
     # :nodoc:
     def self.pthread_join(thread : LibC::PthreadT) : Void*
       ret = LibGC.pthread_join(thread, out value)
-      raise Errno.new("pthread_join") unless ret == 0
+      raise Errno.new("pthread_join", ret) unless ret == 0
       value
     end
 
diff --git a/src/thread.cr b/src/thread.cr
index 28f9fbf62a0a..ed33b6d11f09 100644
--- a/src/thread.cr
+++ b/src/thread.cr
@@ -32,7 +32,7 @@ class Thread
     if ret == 0
       @@threads.push(self)
     else
-      raise Errno.new("pthread_create")
+      raise Errno.new("pthread_create", ret)
     end
   end
 
@@ -67,7 +67,7 @@ class Thread
 
     @@current_key = begin
       ret = LibC.pthread_key_create(out current_key, nil)
-      raise Errno.new("pthread_key_create") unless ret == 0
+      raise Errno.new("pthread_key_create", ret) unless ret == 0
       current_key
     end
 
@@ -83,7 +83,7 @@ class Thread
     # Associates the Thread object to the running system thread.
     protected def self.current=(thread : Thread) : Thread
       ret = LibC.pthread_setspecific(@@current_key, thread.as(Void*))
-      raise Errno.new("pthread_setspecific") unless ret == 0
+      raise Errno.new("pthread_setspecific", ret) unless ret == 0
       thread
     end
   {% else %}
diff --git a/src/thread/condition_variable.cr b/src/thread/condition_variable.cr
index 2eb8c26d72d4..8f6f9c4a8000 100644
--- a/src/thread/condition_variable.cr
+++ b/src/thread/condition_variable.cr
@@ -5,33 +5,28 @@ class Thread
   # :nodoc:
   class ConditionVariable
     def initialize
-      if LibC.pthread_cond_init(out @cond, nil) != 0
-        raise Errno.new("pthread_cond_init")
-      end
+      ret = LibC.pthread_cond_init(out @cond, nil)
+      raise Errno.new("pthread_cond_init", ret) unless ret == 0
     end
 
     def signal
-      if LibC.pthread_cond_signal(self) != 0
-        raise Errno.new("pthread_cond_signal")
-      end
+      ret = LibC.pthread_cond_signal(self)
+      raise Errno.new("pthread_cond_signal", ret) unless ret == 0
     end
 
     def broadcast
-      if LibC.pthread_cond_broadcast(self) != 0
-        raise Errno.new("pthread_cond_broadcast")
-      end
+      ret = LibC.pthread_cond_broadcast(self)
+      raise Errno.new("pthread_cond_broadcast", ret) unless ret == 0
     end
 
     def wait(mutex : Thread::Mutex)
-      if LibC.pthread_cond_wait(self, mutex) != 0
-        raise Errno.new("pthread_cond_wait")
-      end
+      ret = LibC.pthread_cond_wait(self, mutex)
+      raise Errno.new("pthread_cond_wait", ret) unless ret == 0
     end
 
     def finalize
-      if LibC.pthread_cond_destroy(self) != 0
-        raise Errno.new("pthread_cond_broadcast")
-      end
+      ret = LibC.pthread_cond_destroy(self)
+      raise Errno.new("pthread_cond_broadcast", ret) unless ret == 0
     end
 
     def to_unsafe
diff --git a/src/thread/mutex.cr b/src/thread/mutex.cr
index f1241a0c6549..3c53f80fd55f 100644
--- a/src/thread/mutex.cr
+++ b/src/thread/mutex.cr
@@ -5,27 +5,29 @@ class Thread
   # :nodoc:
   class Mutex
     def initialize
-      if LibC.pthread_mutex_init(out @mutex, nil) != 0
-        raise Errno.new("pthread_mutex_init")
-      end
+      ret = LibC.pthread_mutex_init(out @mutex, nil)
+      raise Errno.new("pthread_mutex_init", ret) unless ret == 0
     end
 
     def lock
-      if LibC.pthread_mutex_lock(self) != 0
-        raise Errno.new("pthread_mutex_lock")
-      end
+      ret = LibC.pthread_mutex_lock(self)
+      raise Errno.new("pthread_mutex_lock", ret) unless ret == 0
     end
 
     def try_lock
-      if LibC.pthread_mutex_trylock(self) != 0
-        raise Errno.new("pthread_mutex_trylock")
+      case ret = LibC.pthread_mutex_trylock(self)
+      when 0
+        true
+      when Errno::EBUSY
+        false
+      else
+        raise Errno.new("pthread_mutex_trylock", ret)
       end
     end
 
     def unlock
-      if LibC.pthread_mutex_unlock(self) != 0
-        raise Errno.new("pthread_mutex_unlock")
-      end
+      ret = LibC.pthread_mutex_unlock(self)
+      raise Errno.new("pthread_mutex_unlock", ret) unless ret == 0
     end
 
     def synchronize
@@ -36,9 +38,8 @@ class Thread
     end
 
     def finalize
-      if LibC.pthread_mutex_destroy(self) != 0
-        raise Errno.new("pthread_mutex_destroy")
-      end
+      ret = LibC.pthread_mutex_destroy(self)
+      raise Errno.new("pthread_mutex_destroy", ret) unless ret == 0
     end
 
     def to_unsafe

From 4e55ba4c834051d53134704b27260f82256ea13c Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Sun, 14 Oct 2018 16:08:31 +0200
Subject: [PATCH 2/4] Add error checking to POSIX thread mutexes

Prevents deadlocks and undefined mutex behavior.

> A thread attempting to relock this mutex without first
> unlocking it shall return with an error. A thread attempting
> to unlock a mutex which another thread has locked shall
> return with an error. A thread attempting to unlock an
> unlocked mutex shall return with an error.
>
> http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_mutexattr_settype.html
---
 spec/std/thread/mutex_spec.cr                 | 36 +++++++++++++++++++
 src/lib_c/aarch64-linux-gnu/c/pthread.cr      |  5 +++
 src/lib_c/aarch64-linux-musl/c/pthread.cr     |  5 +++
 src/lib_c/amd64-unknown-openbsd/c/pthread.cr  |  5 +++
 src/lib_c/arm-linux-gnueabihf/c/pthread.cr    |  5 +++
 src/lib_c/i686-linux-gnu/c/pthread.cr         |  5 +++
 src/lib_c/i686-linux-musl/c/pthread.cr        |  5 +++
 src/lib_c/x86_64-linux-gnu/c/pthread.cr       |  5 +++
 src/lib_c/x86_64-linux-musl/c/pthread.cr      |  5 +++
 src/lib_c/x86_64-macosx-darwin/c/pthread.cr   |  5 +++
 src/lib_c/x86_64-portbld-freebsd/c/pthread.cr |  5 +++
 src/thread/mutex.cr                           |  8 ++++-
 12 files changed, 93 insertions(+), 1 deletion(-)
 create mode 100644 spec/std/thread/mutex_spec.cr

diff --git a/spec/std/thread/mutex_spec.cr b/spec/std/thread/mutex_spec.cr
new file mode 100644
index 000000000000..0aaba3ae2fc5
--- /dev/null
+++ b/spec/std/thread/mutex_spec.cr
@@ -0,0 +1,36 @@
+require "spec"
+
+describe Thread::Mutex do
+  it "synchronizes" do
+    a = 0
+    mutex = Thread::Mutex.new
+
+    threads = 10.times.map do
+      Thread.new do
+        mutex.synchronize { a += 1 }
+      end
+    end.to_a
+
+    threads.each(&.join)
+    a.should eq(10)
+  end
+
+  it "won't lock recursively" do
+    mutex = Thread::Mutex.new
+    mutex.try_lock.should be_true
+    mutex.try_lock.should be_false
+    expect_raises(Errno) { mutex.lock }
+    mutex.unlock
+  end
+
+  it "won't unlock from another thread" do
+    mutex = Thread::Mutex.new
+    mutex.lock
+
+    expect_raises(Errno) do
+      Thread.new { mutex.unlock }.join
+    end
+
+    mutex.unlock
+  end
+end
diff --git a/src/lib_c/aarch64-linux-gnu/c/pthread.cr b/src/lib_c/aarch64-linux-gnu/c/pthread.cr
index 75146db23d80..5aafb4b6946f 100644
--- a/src/lib_c/aarch64-linux-gnu/c/pthread.cr
+++ b/src/lib_c/aarch64-linux-gnu/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
@@ -10,6 +12,9 @@ lib LibC
   fun pthread_detach(th : PthreadT) : Int
   fun pthread_equal(thread1 : PthreadT, thread2 : PthreadT) : Int
   fun pthread_join(th : PthreadT, thread_return : Void**) : Int
+  fun pthread_mutexattr_destroy(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(attr : PthreadMutexattrT*, type : Int) : Int
   fun pthread_mutex_destroy(mutex : PthreadMutexT*) : Int
   fun pthread_mutex_init(mutex : PthreadMutexT*, mutexattr : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(mutex : PthreadMutexT*) : Int
diff --git a/src/lib_c/aarch64-linux-musl/c/pthread.cr b/src/lib_c/aarch64-linux-musl/c/pthread.cr
index d2e9d6e30ccc..bc3c3669110b 100644
--- a/src/lib_c/aarch64-linux-musl/c/pthread.cr
+++ b/src/lib_c/aarch64-linux-musl/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/lib_c/amd64-unknown-openbsd/c/pthread.cr b/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
index a0acaf9134b1..6b7e8947c714 100644
--- a/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
+++ b/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
@@ -2,6 +2,8 @@ require "./sys/types"
 
 @[Link("pthread")]
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 1
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -14,6 +16,9 @@ lib LibC
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
   alias PthreadKeyDestructor = (Void*) ->
   fun pthread_key_create(PthreadKeyT*, PthreadKeyDestructor) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/lib_c/arm-linux-gnueabihf/c/pthread.cr b/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
index 75146db23d80..5aafb4b6946f 100644
--- a/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
+++ b/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
@@ -10,6 +12,9 @@ lib LibC
   fun pthread_detach(th : PthreadT) : Int
   fun pthread_equal(thread1 : PthreadT, thread2 : PthreadT) : Int
   fun pthread_join(th : PthreadT, thread_return : Void**) : Int
+  fun pthread_mutexattr_destroy(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(attr : PthreadMutexattrT*, type : Int) : Int
   fun pthread_mutex_destroy(mutex : PthreadMutexT*) : Int
   fun pthread_mutex_init(mutex : PthreadMutexT*, mutexattr : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(mutex : PthreadMutexT*) : Int
diff --git a/src/lib_c/i686-linux-gnu/c/pthread.cr b/src/lib_c/i686-linux-gnu/c/pthread.cr
index b893050a4ba4..87e847a7af42 100644
--- a/src/lib_c/i686-linux-gnu/c/pthread.cr
+++ b/src/lib_c/i686-linux-gnu/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
   fun pthread_join(th : PthreadT, thread_return : Void**) : Int
+  fun pthread_mutexattr_destroy(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(attr : PthreadMutexattrT*, type : Int) : Int
   fun pthread_mutex_destroy(mutex : PthreadMutexT*) : Int
   fun pthread_mutex_init(mutex : PthreadMutexT*, mutexattr : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(mutex : PthreadMutexT*) : Int
diff --git a/src/lib_c/i686-linux-musl/c/pthread.cr b/src/lib_c/i686-linux-musl/c/pthread.cr
index d2e9d6e30ccc..bc3c3669110b 100644
--- a/src/lib_c/i686-linux-musl/c/pthread.cr
+++ b/src/lib_c/i686-linux-musl/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/lib_c/x86_64-linux-gnu/c/pthread.cr b/src/lib_c/x86_64-linux-gnu/c/pthread.cr
index b893050a4ba4..87e847a7af42 100644
--- a/src/lib_c/x86_64-linux-gnu/c/pthread.cr
+++ b/src/lib_c/x86_64-linux-gnu/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
   fun pthread_join(th : PthreadT, thread_return : Void**) : Int
+  fun pthread_mutexattr_destroy(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(attr : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(attr : PthreadMutexattrT*, type : Int) : Int
   fun pthread_mutex_destroy(mutex : PthreadMutexT*) : Int
   fun pthread_mutex_init(mutex : PthreadMutexT*, mutexattr : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(mutex : PthreadMutexT*) : Int
diff --git a/src/lib_c/x86_64-linux-musl/c/pthread.cr b/src/lib_c/x86_64-linux-musl/c/pthread.cr
index d2e9d6e30ccc..bc3c3669110b 100644
--- a/src/lib_c/x86_64-linux-musl/c/pthread.cr
+++ b/src/lib_c/x86_64-linux-musl/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 2
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/lib_c/x86_64-macosx-darwin/c/pthread.cr b/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
index d2e9d6e30ccc..cac58cd1518c 100644
--- a/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
+++ b/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
@@ -1,6 +1,8 @@
 require "./sys/types"
 
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 1
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -9,6 +11,9 @@ lib LibC
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr b/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
index c1471a4083c5..f5805dbf6558 100644
--- a/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
+++ b/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
@@ -2,6 +2,8 @@ require "./sys/types"
 
 @[Link("pthread")]
 lib LibC
+  PTHREAD_MUTEX_ERRORCHECK = 1
+
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
@@ -10,6 +12,9 @@ lib LibC
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
   fun pthread_join(x0 : PthreadT, x1 : Void**) : Int
+  fun pthread_mutexattr_destroy(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_init(x0 : PthreadMutexattrT*) : Int
+  fun pthread_mutexattr_settype(x0 : PthreadMutexattrT*, x1 : Int) : Int
   fun pthread_mutex_destroy(x0 : PthreadMutexT*) : Int
   fun pthread_mutex_init(x0 : PthreadMutexT*, x1 : PthreadMutexattrT*) : Int
   fun pthread_mutex_lock(x0 : PthreadMutexT*) : Int
diff --git a/src/thread/mutex.cr b/src/thread/mutex.cr
index 3c53f80fd55f..ab18f9501fbe 100644
--- a/src/thread/mutex.cr
+++ b/src/thread/mutex.cr
@@ -5,8 +5,14 @@ class Thread
   # :nodoc:
   class Mutex
     def initialize
-      ret = LibC.pthread_mutex_init(out @mutex, nil)
+      attributes = uninitialized LibC::PthreadMutexattrT
+      LibC.pthread_mutexattr_init(pointerof(attributes))
+      LibC.pthread_mutexattr_settype(pointerof(attributes), LibC::PTHREAD_MUTEX_ERRORCHECK)
+
+      ret = LibC.pthread_mutex_init(out @mutex, pointerof(attributes))
       raise Errno.new("pthread_mutex_init", ret) unless ret == 0
+
+      LibC.pthread_mutexattr_destroy(pointerof(attributes))
     end
 
     def lock

From 68d3be32c3f34b3ec97d397bcf7d467ac73d347f Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Sun, 14 Oct 2018 18:01:37 +0200
Subject: [PATCH 3/4] Add Thread.yield

---
 spec/std/thread_spec.cr                     | 15 +++++++++++++++
 src/lib_c/aarch64-linux-gnu/c/sched.cr      |  3 +++
 src/lib_c/aarch64-linux-musl/c/sched.cr     |  3 +++
 src/lib_c/amd64-unknown-openbsd/c/sched.cr  |  3 +++
 src/lib_c/arm-linux-gnueabihf/c/sched.cr    |  3 +++
 src/lib_c/i686-linux-gnu/c/sched.cr         |  3 +++
 src/lib_c/i686-linux-musl/c/sched.cr        |  3 +++
 src/lib_c/x86_64-linux-gnu/c/sched.cr       |  3 +++
 src/lib_c/x86_64-linux-musl/c/sched.cr      |  3 +++
 src/lib_c/x86_64-macosx-darwin/c/sched.cr   |  3 +++
 src/lib_c/x86_64-portbld-freebsd/c/sched.cr |  3 +++
 src/thread.cr                               |  6 ++++++
 12 files changed, 51 insertions(+)
 create mode 100644 src/lib_c/aarch64-linux-gnu/c/sched.cr
 create mode 100644 src/lib_c/aarch64-linux-musl/c/sched.cr
 create mode 100644 src/lib_c/amd64-unknown-openbsd/c/sched.cr
 create mode 100644 src/lib_c/arm-linux-gnueabihf/c/sched.cr
 create mode 100644 src/lib_c/i686-linux-gnu/c/sched.cr
 create mode 100644 src/lib_c/i686-linux-musl/c/sched.cr
 create mode 100644 src/lib_c/x86_64-linux-gnu/c/sched.cr
 create mode 100644 src/lib_c/x86_64-linux-musl/c/sched.cr
 create mode 100644 src/lib_c/x86_64-macosx-darwin/c/sched.cr
 create mode 100644 src/lib_c/x86_64-portbld-freebsd/c/sched.cr

diff --git a/spec/std/thread_spec.cr b/spec/std/thread_spec.cr
index 47e1db6d6bf3..c84e5002f3be 100644
--- a/spec/std/thread_spec.cr
+++ b/spec/std/thread_spec.cr
@@ -22,4 +22,19 @@ describe Thread do
     current.should be(thread)
     current.should_not be(Thread.current)
   end
+
+  it "yields the processor" do
+    done = false
+
+    thread = Thread.new do
+      3.times { Thread.yield }
+      done = true
+    end
+
+    until done
+      Thread.yield
+    end
+
+    thread.join
+  end
 end
diff --git a/src/lib_c/aarch64-linux-gnu/c/sched.cr b/src/lib_c/aarch64-linux-gnu/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/aarch64-linux-gnu/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/aarch64-linux-musl/c/sched.cr b/src/lib_c/aarch64-linux-musl/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/aarch64-linux-musl/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/amd64-unknown-openbsd/c/sched.cr b/src/lib_c/amd64-unknown-openbsd/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/amd64-unknown-openbsd/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/arm-linux-gnueabihf/c/sched.cr b/src/lib_c/arm-linux-gnueabihf/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/arm-linux-gnueabihf/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/i686-linux-gnu/c/sched.cr b/src/lib_c/i686-linux-gnu/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/i686-linux-gnu/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/i686-linux-musl/c/sched.cr b/src/lib_c/i686-linux-musl/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/i686-linux-musl/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/x86_64-linux-gnu/c/sched.cr b/src/lib_c/x86_64-linux-gnu/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/x86_64-linux-gnu/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/x86_64-linux-musl/c/sched.cr b/src/lib_c/x86_64-linux-musl/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/x86_64-linux-musl/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/x86_64-macosx-darwin/c/sched.cr b/src/lib_c/x86_64-macosx-darwin/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/x86_64-macosx-darwin/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/lib_c/x86_64-portbld-freebsd/c/sched.cr b/src/lib_c/x86_64-portbld-freebsd/c/sched.cr
new file mode 100644
index 000000000000..9d83ed18504e
--- /dev/null
+++ b/src/lib_c/x86_64-portbld-freebsd/c/sched.cr
@@ -0,0 +1,3 @@
+lib LibC
+  fun sched_yield : Int
+end
diff --git a/src/thread.cr b/src/thread.cr
index ed33b6d11f09..2fe324249879 100644
--- a/src/thread.cr
+++ b/src/thread.cr
@@ -1,4 +1,5 @@
 require "c/pthread"
+require "c/sched"
 require "./thread/*"
 
 # :nodoc:
@@ -106,6 +107,11 @@ class Thread
   # TODO: consider moving to `kernel.cr` or `crystal/main.cr`
   self.current = new
 
+  def self.yield
+    ret = LibC.sched_yield
+    raise Errno.new("sched_yield") unless ret == 0
+  end
+
   # Returns the Fiber representing the thread's main stack.
   def main_fiber
     @main_fiber.not_nil!

From 41045d65b0b635348314271f429e201f62d90fce Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Sun, 14 Oct 2018 16:25:50 +0200
Subject: [PATCH 4/4] Add Thread::ConditionVariable#wait with timeout.

Configures thread condition variables to use the monotonic clock.

Adds an overload for `#wait` that takes a timeout and executes the
block when the timeout is reached, but doesn't when the condition
variable is normally resumed.

Refactors & enables Thread::ConditionVariable specs so they don't
randomly hang.
---
 spec/std/thread/condition_variable_spec.cr    | 115 +++++++++---------
 src/lib_c/aarch64-linux-gnu/c/pthread.cr      |   4 +
 src/lib_c/aarch64-linux-musl/c/pthread.cr     |   4 +
 src/lib_c/amd64-unknown-openbsd/c/pthread.cr  |   4 +
 src/lib_c/arm-linux-gnueabihf/c/pthread.cr    |   4 +
 src/lib_c/i686-linux-gnu/c/pthread.cr         |   4 +
 src/lib_c/i686-linux-musl/c/pthread.cr        |   4 +
 src/lib_c/x86_64-linux-gnu/c/pthread.cr       |   4 +
 src/lib_c/x86_64-linux-musl/c/pthread.cr      |   4 +
 src/lib_c/x86_64-macosx-darwin/c/pthread.cr   |   3 +
 src/lib_c/x86_64-portbld-freebsd/c/pthread.cr |   4 +
 src/thread/condition_variable.cr              |  42 ++++++-
 12 files changed, 137 insertions(+), 59 deletions(-)

diff --git a/spec/std/thread/condition_variable_spec.cr b/spec/std/thread/condition_variable_spec.cr
index 9588c5e0f638..d5f7a5018fbd 100644
--- a/spec/std/thread/condition_variable_spec.cr
+++ b/spec/std/thread/condition_variable_spec.cr
@@ -1,90 +1,89 @@
 require "spec"
 
-# These specs are marked as pending until we add
-# support for parallelism, where we'll see if we
-# need condition variables.
-#
-# Also: review these specs!
 describe Thread::ConditionVariable do
-  pending "signals" do
+  it "signals" do
     mutex = Thread::Mutex.new
     cond = Thread::ConditionVariable.new
-    pcond = Thread::ConditionVariable.new
-    waiting = 0
-    signaled = 0
 
-    threads = 3.times.map do
+    mutex.synchronize do
       Thread.new do
-        mutex.synchronize do
-          waiting += 1
-          # TODO: why is this needed? Bug?
-          pcond.signal
-          cond.wait mutex
-        end
+        mutex.synchronize { cond.signal }
       end
-    end.to_a
 
-    while signaled < 3
-      mutex.synchronize do
-        if waiting > 0
-          waiting -= 1
-          signaled += 1
-          cond.signal
-        end
-      end
+      cond.wait(mutex)
     end
-    threads.map &.join
   end
 
-  pending "broadcasts" do
+  it "signals & broadcasts" do
     mutex = Thread::Mutex.new
-    cond = Thread::ConditionVariable.new
-    pcond = Thread::ConditionVariable.new
+    cv1 = Thread::ConditionVariable.new
+    cv2 = Thread::ConditionVariable.new
     waiting = 0
-    signaled = false
 
-    threads = 3.times.map do
+    5.times do
       Thread.new do
         mutex.synchronize do
           waiting += 1
-          pcond.signal
-          cond.wait mutex
+          cv1.wait(mutex)
+
+          waiting -= 1
+          cv2.signal
         end
       end
-    end.to_a
-
-    until signaled
-      mutex.synchronize do
-        if waiting >= 3
-          cond.broadcast
-          signaled = true
-        else
-          pcond.wait mutex
-        end
+    end
+
+    # wait for all threads to have acquired the mutex and be waiting on the
+    # condition variable, otherwise the main thread could acquire the lock
+    # first, and signal into the void.
+    #
+    # since increments to waiting are synchronized, at least 4 threads are
+    # guaranteed to be waiting when waiting is 5, which is enough for futher
+    # tests to never hangup.
+    until waiting == 5
+      Thread.yield
+    end
+
+    # wakes up at least 1 thread:
+    mutex.synchronize do
+      cv1.signal
+      cv2.wait(mutex)
+    end
+    waiting.should be < 5
+
+    # wakes up all waiting threads:
+    mutex.synchronize do
+      cv1.broadcast
+
+      until waiting == 0
+        cv2.wait(mutex, 1.second) { raise "unexpected wait timeout" }
       end
     end
+  end
+
+  it "timeouts" do
+    timedout = false
+    mutex = Thread::Mutex.new
+    cond = Thread::ConditionVariable.new
 
-    threads.map &.join
+    mutex.synchronize do
+      cond.wait(mutex, 1.microsecond) { timedout = true }
+    end
+    timedout.should be_true
   end
 
-  pending "waits and send signal" do
-    a = 0
-    cv1 = Thread::ConditionVariable.new
-    cv2 = Thread::ConditionVariable.new
-    m = Thread::Mutex.new
+  it "resumes before timeout" do
+    timedout = false
+    mutex = Thread::Mutex.new
+    cond = Thread::ConditionVariable.new
 
-    thread = Thread.new do
-      3.times do
-        m.synchronize { cv1.wait(m); a += 1; cv2.signal }
+    mutex.synchronize do
+      Thread.new do
+        mutex.synchronize { cond.signal }
       end
-    end
 
-    a.should eq(0)
-    3.times do |i|
-      m.synchronize { cv1.signal; cv2.wait(m) }
-      a.should eq(i + 1)
+      cond.wait(mutex, 1.second) { timedout = true }
     end
 
-    thread.join
+    timedout.should be_false
   end
 end
diff --git a/src/lib_c/aarch64-linux-gnu/c/pthread.cr b/src/lib_c/aarch64-linux-gnu/c/pthread.cr
index 5aafb4b6946f..003ab9aa223b 100644
--- a/src/lib_c/aarch64-linux-gnu/c/pthread.cr
+++ b/src/lib_c/aarch64-linux-gnu/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(attr : PthreadCondattrT*, type : ClockidT) : Int
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
   fun pthread_cond_signal(cond : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(cond : PthreadCondT*, mutex : PthreadMutexT*, abstime : Timespec*) : Int
   fun pthread_cond_wait(cond : PthreadCondT*, mutex : PthreadMutexT*) : Int
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
diff --git a/src/lib_c/aarch64-linux-musl/c/pthread.cr b/src/lib_c/aarch64-linux-musl/c/pthread.cr
index bc3c3669110b..d5da49a49319 100644
--- a/src/lib_c/aarch64-linux-musl/c/pthread.cr
+++ b/src/lib_c/aarch64-linux-musl/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(x0 : PthreadCondattrT*, x1 : ClockidT) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/lib_c/amd64-unknown-openbsd/c/pthread.cr b/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
index 6b7e8947c714..018ec685694a 100644
--- a/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
+++ b/src/lib_c/amd64-unknown-openbsd/c/pthread.cr
@@ -4,10 +4,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 1
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(x0 : PthreadCondattrT*, x1 : ClockidT) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/lib_c/arm-linux-gnueabihf/c/pthread.cr b/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
index 5aafb4b6946f..003ab9aa223b 100644
--- a/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
+++ b/src/lib_c/arm-linux-gnueabihf/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(attr : PthreadCondattrT*, type : ClockidT) : Int
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
   fun pthread_cond_signal(cond : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(cond : PthreadCondT*, mutex : PthreadMutexT*, abstime : Timespec*) : Int
   fun pthread_cond_wait(cond : PthreadCondT*, mutex : PthreadMutexT*) : Int
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
diff --git a/src/lib_c/i686-linux-gnu/c/pthread.cr b/src/lib_c/i686-linux-gnu/c/pthread.cr
index 87e847a7af42..944f2ce9c30b 100644
--- a/src/lib_c/i686-linux-gnu/c/pthread.cr
+++ b/src/lib_c/i686-linux-gnu/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(attr : PthreadCondattrT*, type : ClockidT) : Int
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
   fun pthread_cond_signal(cond : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(cond : PthreadCondT*, mutex : PthreadMutexT*, abstime : Timespec*) : Int
   fun pthread_cond_wait(cond : PthreadCondT*, mutex : PthreadMutexT*) : Int
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
diff --git a/src/lib_c/i686-linux-musl/c/pthread.cr b/src/lib_c/i686-linux-musl/c/pthread.cr
index bc3c3669110b..d5da49a49319 100644
--- a/src/lib_c/i686-linux-musl/c/pthread.cr
+++ b/src/lib_c/i686-linux-musl/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(x0 : PthreadCondattrT*, x1 : ClockidT) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/lib_c/x86_64-linux-gnu/c/pthread.cr b/src/lib_c/x86_64-linux-gnu/c/pthread.cr
index 87e847a7af42..944f2ce9c30b 100644
--- a/src/lib_c/x86_64-linux-gnu/c/pthread.cr
+++ b/src/lib_c/x86_64-linux-gnu/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(attr : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(attr : PthreadCondattrT*, type : ClockidT) : Int
   fun pthread_cond_broadcast(cond : PthreadCondT*) : Int
   fun pthread_cond_destroy(cond : PthreadCondT*) : Int
   fun pthread_cond_init(cond : PthreadCondT*, cond_attr : PthreadCondattrT*) : Int
   fun pthread_cond_signal(cond : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(cond : PthreadCondT*, mutex : PthreadMutexT*, abstime : Timespec*) : Int
   fun pthread_cond_wait(cond : PthreadCondT*, mutex : PthreadMutexT*) : Int
   fun pthread_create(newthread : PthreadT*, attr : PthreadAttrT*, start_routine : Void* -> Void*, arg : Void*) : Int
   fun pthread_detach(th : PthreadT) : Int
diff --git a/src/lib_c/x86_64-linux-musl/c/pthread.cr b/src/lib_c/x86_64-linux-musl/c/pthread.cr
index bc3c3669110b..d5da49a49319 100644
--- a/src/lib_c/x86_64-linux-musl/c/pthread.cr
+++ b/src/lib_c/x86_64-linux-musl/c/pthread.cr
@@ -3,10 +3,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 2
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(x0 : PthreadCondattrT*, x1 : ClockidT) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/lib_c/x86_64-macosx-darwin/c/pthread.cr b/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
index cac58cd1518c..5ca68fa77ce2 100644
--- a/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
+++ b/src/lib_c/x86_64-macosx-darwin/c/pthread.cr
@@ -3,10 +3,13 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 1
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait_relative_np(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr b/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
index f5805dbf6558..4c7a012c2424 100644
--- a/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
+++ b/src/lib_c/x86_64-portbld-freebsd/c/pthread.cr
@@ -4,10 +4,14 @@ require "./sys/types"
 lib LibC
   PTHREAD_MUTEX_ERRORCHECK = 1
 
+  fun pthread_condattr_destroy(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_init(x0 : PthreadCondattrT*) : Int
+  fun pthread_condattr_setclock(x0 : PthreadCondattrT*, x1 : ClockidT) : Int
   fun pthread_cond_broadcast(x0 : PthreadCondT*) : Int
   fun pthread_cond_destroy(x0 : PthreadCondT*) : Int
   fun pthread_cond_init(x0 : PthreadCondT*, x1 : PthreadCondattrT*) : Int
   fun pthread_cond_signal(x0 : PthreadCondT*) : Int
+  fun pthread_cond_timedwait(x0 : PthreadCondT*, x1 : PthreadMutexT*, x2 : Timespec*) : Int
   fun pthread_cond_wait(x0 : PthreadCondT*, x1 : PthreadMutexT*) : Int
   fun pthread_create(x0 : PthreadT*, x1 : PthreadAttrT*, x2 : Void* -> Void*, x3 : Void*) : Int
   fun pthread_detach(x0 : PthreadT) : Int
diff --git a/src/thread/condition_variable.cr b/src/thread/condition_variable.cr
index 8f6f9c4a8000..5c8da3365dd4 100644
--- a/src/thread/condition_variable.cr
+++ b/src/thread/condition_variable.cr
@@ -5,8 +5,17 @@ class Thread
   # :nodoc:
   class ConditionVariable
     def initialize
-      ret = LibC.pthread_cond_init(out @cond, nil)
+      attributes = uninitialized LibC::PthreadCondattrT
+      LibC.pthread_condattr_init(pointerof(attributes))
+
+      {% unless flag?(:darwin) %}
+        LibC.pthread_condattr_setclock(pointerof(attributes), LibC::CLOCK_MONOTONIC)
+      {% end %}
+
+      ret = LibC.pthread_cond_init(out @cond, pointerof(attributes))
       raise Errno.new("pthread_cond_init", ret) unless ret == 0
+
+      LibC.pthread_condattr_destroy(pointerof(attributes))
     end
 
     def signal
@@ -24,6 +33,37 @@ class Thread
       raise Errno.new("pthread_cond_wait", ret) unless ret == 0
     end
 
+    def wait(mutex : Thread::Mutex, time : Time::Span)
+      ret =
+        {% if flag?(:darwin) %}
+          ts = uninitialized LibC::Timespec
+          ts.tv_sec = time.to_i
+          ts.tv_nsec = time.nanoseconds
+
+          LibC.pthread_cond_timedwait_relative_np(self, mutex, pointerof(ts))
+        {% else %}
+          LibC.clock_gettime(LibC::CLOCK_MONOTONIC, out ts)
+          ts.tv_sec += time.to_i
+          ts.tv_nsec += time.nanoseconds
+
+          if ts.tv_nsec >= 1_000_000_000
+            ts.tv_sec += 1
+            ts.tv_nsec -= 1_000_000_000
+          end
+
+          LibC.pthread_cond_timedwait(self, mutex, pointerof(ts))
+        {% end %}
+
+      case ret
+      when 0
+        # normal resume from #signal or #broadcast
+      when Errno::ETIMEDOUT
+        yield
+      else
+        raise Errno.new("pthread_cond_timedwait", ret)
+      end
+    end
+
     def finalize
       ret = LibC.pthread_cond_destroy(self)
       raise Errno.new("pthread_cond_broadcast", ret) unless ret == 0