Add C++ lock examples

Makefile

@@ -72,6 +72,8 @@ ch01/alarm_fork_cpp.cpp \
 ch01/alarm_thread_cpp.cpp \
 ch02/hello_cpp.cpp \
 ch02/lifecycle_cpp.cpp \
+ch03/backoff_cpp.cpp \
+ch03/trylock_cpp.cpp \
 ch03/alarm_mutex_cpp.cpp \
 ch04/pipe_cpp.cpp
 

src/ch03/backoff_cpp.cpp

@@ -0,0 +1,194 @@
+
+#include "errors.hpp"
+
+#include <chrono>
+#include <iostream>
+#include <mutex>
+#include <thread>
+
+#define ITERATIONS 10
+
+/*
+ * Initialize a static array of 3 mutexes.
+ */
+std::mutex mutex[3];
+
+int backoff    = 1; /* Whether to backoff or deadlock */
+int yield_flag = 0; /* 0: no yield, >0: yield, <0: sleep */
+
+/*
+ * This is a thread start routine that locks all mutexes in
+ * order, to ensure a conflict with lock_reverse, which does the
+ * opposite.
+ */
+
+void
+lock_forward_new()
+{
+  for (int iterate = 0; iterate < ITERATIONS; iterate++) {
+    std::lock(mutex[0], mutex[1], mutex[2]);
+    std::lock_guard<std::mutex> l0(mutex[0], std::adopt_lock);
+    std::lock_guard<std::mutex> l1(mutex[1], std::adopt_lock);
+    std::lock_guard<std::mutex> l2(mutex[2], std::adopt_lock);
+    std::cout << "new lock forward got all locks" << std::endl;
+  }
+}
+
+void
+lock_forward()
+{
+  for (int iterate = 0; iterate < ITERATIONS; iterate++) {
+    int backoffs = 0;
+    for (int i = 0; i < 3; i++) {
+      if (i == 0) {
+        mutex[i].lock();
+      }
+      else {
+        bool isFree = true;
+        if (backoff)
+          isFree = mutex[i].try_lock();
+        else
+          mutex[i].lock();
+        if (!isFree) {
+          backoffs++;
+          std::cout << " [forward locker backing off at " << i << "]"
+                    << std::endl;
+          for (; i >= 0; i--) {
+            mutex[i].unlock();
+          }
+        }
+        else {
+          std::cout << " forward locker got " << i << std::endl;
+        }
+      }
+      /*
+       * Yield processor, if needed to be sure locks get
+       * interleaved on a uniprocessor.
+       */
+      if (yield_flag) {
+        if (yield_flag > 0)
+          std::this_thread::yield();
+        else
+          std::this_thread::sleep_for(std::chrono::seconds(1));
+      }
+    }
+    /*
+     * Report that we got 'em, and unlock to try again.
+     */
+    std::cout << "lock forward got all locks, " << backoffs << " backoffs"
+              << std::endl;
+    mutex[2].unlock();
+    mutex[1].unlock();
+    mutex[0].unlock();
+    std::this_thread::yield();
+  }
+}
+
+void
+lock_backward_new()
+{
+  for (int iterate = 0; iterate < ITERATIONS; iterate++) {
+    std::lock(mutex[2], mutex[1], mutex[0]);
+    std::lock_guard<std::mutex> l2(mutex[2], std::adopt_lock);
+    std::lock_guard<std::mutex> l1(mutex[1], std::adopt_lock);
+    std::lock_guard<std::mutex> l0(mutex[0], std::adopt_lock);
+    std::cout << "new lock backward got all locks" << std::endl;
+  }
+}
+
+/*
+ * This is a thread start routine that locks all mutexes in
+ * reverse order, to ensure a conflict with lock_forward, which
+ * does the opposite.
+ */
+void
+lock_backward()
+{
+  for (int iterate = 0; iterate < ITERATIONS; iterate++) {
+    int backoffs = 0;
+    for (int i = 2; i >= 0; i--) {
+      if (i == 2) {
+        mutex[i].lock();
+      }
+      else {
+        bool isFree = true;
+        if (backoff)
+          isFree = mutex[i].try_lock();
+        else
+          mutex[i].lock();
+        if (!isFree) {
+          backoffs++;
+          std::cout << " [backward locker backing off at " << i << "]"
+                    << std::endl;
+          for (; i < 3; i++) {
+            mutex[i].unlock();
+          }
+        }
+        else {
+          std::cout << " backward locker got " << i << std::endl;
+        }
+      }
+      /*
+       * Yield processor, if needed to be sure locks get
+       * interleaved on a uniprocessor.
+       */
+      if (yield_flag) {
+        if (yield_flag > 0)
+          std::this_thread::yield();
+        else
+          std::this_thread::sleep_for(std::chrono::seconds(1));
+      }
+    }
+    /*
+     * Report that we got 'em, and unlock to try again.
+     */
+    std::cout << "lock backward got all locks, " << backoffs << " backoffs"
+              << std::endl;
+    mutex[0].unlock();
+    mutex[1].unlock();
+    mutex[2].unlock();
+    std::this_thread::yield();
+  }
+}
+
+int
+main(int argc, char* argv[])
+{
+  /*
+   * If the first argument is absent, or nonzero, a backoff
+   * algorithm will be used to avoid deadlock. If the first
+   * argument is zero, the program will deadlock on a lock
+   * "collision."
+   */
+  if (argc > 1)
+    backoff = atoi(argv[1]);
+
+  /*
+   * If the second argument is absent, or zero, the two
+   * threads run "at speed." On some systems, especially
+   * uniprocessors, one thread may complete before the other
+   * has a chance to run, and you won't see a deadlock or
+   * backoffs. In that case, try running with the argument set
+   * to a positive number to cause the threads to call
+   * sched_yield() at each lock; or, to make it even more
+   * obvious, set to a negative number to cause the threads to
+   * call sleep(1) instead.
+   */
+  if (argc > 2)
+    yield_flag = atoi(argv[2]);
+
+  if (backoff < 0) {
+    std::thread t1(lock_forward_new);
+    std::thread t2(lock_backward_new);
+
+    t1.join();
+    t2.join();
+    return 0;
+  }
+
+  std::thread t1(lock_forward);
+  std::thread t2(lock_backward);
+
+  t1.join();
+  t2.join();
+}

src/ch03/trylock_cpp.cpp

@@ -0,0 +1,79 @@
+
+#include "errors.hpp"
+
+#include <chrono>
+#include <iostream>
+#include <mutex>
+#include <thread>
+
+#define SPIN 10000000
+
+using ClockType = std::chrono::high_resolution_clock;
+
+std::mutex mutex;
+long counter;
+ClockType::time_point end_time;
+
+/*
+ * Thread start routine that repeatedly locks a mutex and
+ * increments a counter.
+ */
+void
+counter_thread()
+{
+  /*
+   * Until end_time, increment the counter each
+   * second. Instead of just incrementing the counter, it
+   * sleeps for another second with the mutex locked, to give
+   * monitor_thread a reasonable chance of running.
+   */
+  while (ClockType::now() < end_time) {
+    {
+      std::lock_guard<std::mutex> l(mutex);
+      for (long spin = 0; spin < SPIN; spin++) counter++;
+      // std::this_thread::sleep_for(std::chrono::seconds(4));
+    }
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+  }
+
+  std::cout << "[Counter] total spins " << counter << std::endl;
+}
+
+/*
+ * Thread start routine to "monitor" the counter. Every 3
+ * seconds, try to lock the mutex and read the counter. If the
+ * trylock fails, skip this cycle.
+ */
+void
+monitor_thread()
+{
+  /*
+   * Loop until end_time, checking the counter every 3
+   * seconds.
+   */
+  int misses = 0;
+  while (ClockType::now() < end_time) {
+    std::this_thread::sleep_for(std::chrono::seconds(3));
+    if (mutex.try_lock()) {
+      std::lock_guard<std::mutex> l(mutex, std::adopt_lock);
+      std::cout << "[Monitor] Counter is " << counter / SPIN << std::endl;
+    }
+    else
+      misses++; /* Count "misses" on the lock */
+  }
+
+  std::cout << "[Monitor] thread missed update " << misses << " times.\n";
+}
+
+int
+main(int argc, char* argv[])
+{
+  end_time = ClockType::now() + std::chrono::seconds(60); /* Run for 1 minute */
+  std::thread t1(counter_thread);
+  std::thread t2(monitor_thread);
+
+  t1.join();
+  t2.join();
+
+  return 0;
+}