Implement shared locks in the style of pthread's rwlock.

tests/SkSharedLockTest.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkSharedLock.h"
+#include "SkTaskGroup.h"
+
+#include "Test.h"
+
+DEF_TEST(SkSharedLockBasic, r) {
+  SkSharedLock sm;

[mtklein, 2015/06/29 16:29:22]

Given that we've already got the precent of 'SkMutex' and we're even
abbreviating this as 'sm', we might consider a doing a
s/SkSharedLock/SkSharedMutex/g.

+  sm.acquire();
+  sm.release();
+  sm.acquireShared();
+  sm.releaseShared();
+}
+
+class LockTester {
+public:
+  LockTester(SkSharedLock* sharedLock, int* shared, int size)
+      : fValue(0)
+      , fSharedLock(sharedLock)
+      , fShared(shared)
+      , fSize(size) { }
+
+  void operator()(int threadIndex) const {
+    if (threadIndex % 4 != 0) {

[mtklein, 2015/06/29 16:29:22]

Time to switch your editor to 4 space indents. :)

[herb_g, 2015/06/29 20:37:06]

Done.

+      for (int c = 0; c < 100000; ++c) {
+        fSharedLock->acquireShared();
+        int v = fShared[0];
+        for (int i = 1; i < fSize; ++i) {
+          SkASSERTF(v == fShared[i], "v: %d i: %d, s[i]: %d", v, i, fShared[i]);

[mtklein, 2015/06/29 16:29:22]

Generally we'd use REPORTER_ASSERT(r, v == fShared[i]).  Otherwise, failures
here kill the whole test harness instead of just failing this test (and
SkASSERTF compiles away to nothing in Release mode).

[herb_g, 2015/06/29 20:37:05]

Done.

+        }
+        fSharedLock->releaseShared();
+      }
+    } else {
+      for (int c = 0; c < 100000; ++c) {
+        fSharedLock->acquire();
+        fValue += 1;
+        for (int i = 0; i < fSize; ++i) {
+          fShared[i] = fValue;
+        }
+        fSharedLock->release();
+      }
+    }
+  }
+
+private:
+  mutable int fValue;
+  mutable SkSharedLock* fSharedLock;
+  int* const fShared;
+  const int fSize;
+};
+
+DEF_TEST(SkSharedLockMultiThreaded, r) {
+  SkSharedLock sm;
+  static const int kSharedSize = 10;
+  int shared[kSharedSize];
+  for (int i = 0; i < kSharedSize; ++i) {
+    shared[i] = 0;
+  }
+  LockTester t(&sm, shared, kSharedSize);
+  sk_parallel_for(8, t);

[mtklein, 2015/06/29 16:29:22]

Any reason to not write this all inline?

DEF_TEST(SkSharedLockMultiThreaded, r) {
  SkSharedLock sm;
  static const int kSharedSize = 10;
  int shared[kSharedSize];
  for (int i = 0; i < kSharedSize; ++i) {
    shared[i] = 0;
  }

  int value = 0;
  sk_parallel_for(8, [&](int threadIndex) {
    if (threadIndex % 4 != 0) {
      for (int c = 0; c < 100000; ++c) {
        sm.acquireShared();
        int v = shared[0];
        for (int i = 1; i < kSharedSize; ++i) {
          SkASSERTF(v == shared[i], "v: %d i: %d, s[i]: %d", v, i, shared[i]);
        }
        sm.releaseShared();
      }
    } else {
      for (int c = 0; c < 100000; ++c) {
        sm.acquire();
        value += 1;
        for (int i = 0; i < kSharedSize; ++i) {
          shared[i] = value;
        }
        sm.release();
      }
    }
 });
}

[herb_g, 2015/06/29 20:37:06]

Done.

+}