job/flag: add a one off event object

CMakeLists.txt

@@ -88,6 +88,7 @@ list (
 if (LINUX)
     list (APPEND UTIL_FILES
         job/event_linux.cpp
+        job/flag_linux.cpp
         )
 endif ()
 
@@ -123,16 +124,17 @@ if (WINDOWS)
         exe_win32.cpp
         io_win32.cpp
         io_win32.hpp
-        library_win32.hpp
+        job/event_win32.cpp
+        job/flag_win32.cpp
         library_win32.cpp
+        library_win32.hpp
         time_win32.cpp
         win32/except.cpp
         win32/except.hpp
         win32/handle.cpp
         win32/handle.hpp
-        win32/registry.hpp
         win32/registry.cpp
-        job/event_win32.cpp
+        win32/registry.hpp
     )
 endif ()
 
@@ -265,6 +267,7 @@ list (
     io.hpp
     iterator.hpp
     job/event.hpp
+    job/flag.hpp
     job/queue.cpp
     job/queue.hpp
     json/fwd.hpp
@@ -475,6 +478,7 @@ if (TESTS)
         introspection
         iterator
         job/event
+        job/flag
         job/queue
         json_types
         json2/event

job/flag.hpp

@@ -0,0 +1,39 @@
+/*
+ * 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.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef CRUFT_UTIL_JOB_FLAG_HPP
+#define CRUFT_UTIL_JOB_FLAG_HPP
+
+#include <atomic>
+
+namespace util::job {
+    /// a fire-once event that users can wait upon. if already fired then
+    /// waiting will be a noop.
+    class flag {
+    public:
+        flag ();
+
+        void wait (void);
+
+        int notify (void);
+        int notify (int);
+
+    private:
+        std::atomic<int> value;
+    };
+};
+
+#endif

job/flag_linux.cpp

@@ -0,0 +1,82 @@
+/*
+ * 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.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "flag.hpp"
+#include "../cast.hpp"
+
+#include <cerrno>
+#include <linux/futex.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <cruft/util/posix/except.hpp>
+#include <limits>
+
+using util::job::flag;
+
+
+///////////////////////////////////////////////////////////////////////////////
+static long
+sys_futex (void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
+{
+    return syscall (SYS_futex, addr1, op | FUTEX_PRIVATE_FLAG, val1, timeout, addr2, val3);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+flag::flag ():
+    value (0)
+{ ; }
+
+
+///////////////////////////////////////////////////////////////////////////////
+void
+flag::wait (void)
+{
+    if (value)
+        return;
+
+    while (!value) {
+        auto res = sys_futex (&value, FUTEX_WAIT, 0, nullptr, nullptr, 0);
+
+        if (res < 0) {
+            switch (errno) {
+            case EAGAIN: return;
+            case EINTR:  continue;
+            }
+
+            posix::error::throw_code ();
+        }
+    }
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+int
+flag::notify (void)
+{
+    return notify (std::numeric_limits<int>::max ());
+}
+
+
+//-----------------------------------------------------------------------------
+int
+flag::notify (int count)
+{
+    value = 1;
+    auto res = sys_futex (&value, FUTEX_WAKE, count, nullptr, nullptr, 0);
+    if (res < 0)
+        posix::error::throw_code ();
+    return util::cast::narrow<int> (res);
+}

test/job/flag.cpp

@@ -0,0 +1,38 @@
+#include "job/flag.hpp"
+#include "tap.hpp"
+
+#include <thread>
+
+
+int
+main ()
+{
+    util::TAP::logger tap;
+
+    util::job::flag f;
+    std::atomic<int> value = 0;
+
+    std::thread t1 ([&] () {
+        f.wait ();
+        value = 1;
+    });
+
+    std::this_thread::sleep_for (std::chrono::milliseconds (100));
+
+    tap.expect_eq (value, 0, "value hasn't been set during wait");
+    tap.expect_eq (f.notify (), 1, "notify reports one thread woke");
+
+    t1.join ();
+    tap.expect_eq (value, 1, "value has been changed after wait");
+
+    std::thread t2 ([&] () {
+        f.wait ();
+        value = 2;
+    });
+
+    std::this_thread::sleep_for (std::chrono::milliseconds (100));
+    tap.expect_eq (value, 2, "second wait didn't appear to block");
+    t2.join ();
+
+    return tap.status ();
+}