1 files changed, 138 insertions, 0 deletions
diff --git a/media/tests/NativeMidiDemo/jni/messagequeue.cpp b/media/tests/NativeMidiDemo/jni/messagequeue.cpp
new file mode 100644
index 000000000000..ffaef38bed8c
--- /dev/null
+++ b/media/tests/NativeMidiDemo/jni/messagequeue.cpp
@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * 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.
+ *
+ */
+
+#include <atomic>
+#include <stdio.h>
+#include <string.h>
+
+#include "messagequeue.h"
+
+namespace nativemididemo {
+
+static const int messageBufferSize = 64 * 1024;
+static char messageBuffer[messageBufferSize];
+static std::atomic_ullong messagesLastWritePosition;
+
+void writeMessage(const char* message)
+{
+    static unsigned long long lastWritePos = 0;
+    size_t messageLen = strlen(message);
+    if (messageLen == 0) return;
+
+    messageLen += 1; // Also count in the null terminator.
+    char buffer[1024];
+    if (messageLen >= messageBufferSize) {
+        snprintf(buffer, sizeof(buffer), "!!! Message too long: %zu bytes !!!", messageLen);
+        message = buffer;
+        messageLen = strlen(message);
+    }
+
+    size_t wrappedWritePos = lastWritePos % messageBufferSize;
+    if (wrappedWritePos + messageLen >= messageBufferSize) {
+        size_t tailLen = messageBufferSize - wrappedWritePos;
+        memset(messageBuffer + wrappedWritePos, 0, tailLen);
+        lastWritePos += tailLen;
+        wrappedWritePos = 0;
+    }
+
+    memcpy(messageBuffer + wrappedWritePos, message, messageLen);
+    lastWritePos += messageLen;
+    messagesLastWritePosition.store(lastWritePos);
+}
+
+static char messageBufferCopy[messageBufferSize];
+
+jobjectArray getRecentMessagesForJava(JNIEnv* env, jobject)
+{
+    static unsigned long long lastReadPos = 0;
+    const char* overrunMessage = "";
+    size_t messagesCount = 0;
+    jobjectArray result = NULL;
+
+    // First we copy the portion of the message buffer into messageBufferCopy.  If after finishing
+    // the copy we notice that the writer has mutated the portion of the buffer that we were
+    // copying, we report an overrun. Afterwards we can safely read messages from the copy.
+    memset(messageBufferCopy, 0, sizeof(messageBufferCopy));
+    unsigned long long lastWritePos = messagesLastWritePosition.load();
+    if (lastWritePos - lastReadPos > messageBufferSize) {
+        overrunMessage = "!!! Message buffer overrun !!!";
+        messagesCount = 1;
+        lastReadPos = lastWritePos;
+        goto create_array;
+    }
+    if (lastWritePos == lastReadPos) return result;
+    if (lastWritePos / messageBufferSize == lastReadPos / messageBufferSize) {
+        size_t wrappedReadPos = lastReadPos % messageBufferSize;
+        memcpy(messageBufferCopy + wrappedReadPos,
+                messageBuffer + wrappedReadPos,
+                lastWritePos % messageBufferSize - wrappedReadPos);
+    } else {
+        size_t wrappedReadPos = lastReadPos % messageBufferSize;
+        memcpy(messageBufferCopy, messageBuffer, lastWritePos % messageBufferSize);
+        memcpy(messageBufferCopy + wrappedReadPos,
+                messageBuffer + wrappedReadPos,
+                messageBufferSize - wrappedReadPos);
+    }
+    {
+    unsigned long long newLastWritePos = messagesLastWritePosition.load();
+    if (newLastWritePos - lastReadPos > messageBufferSize) {
+        overrunMessage = "!!! Message buffer overrun !!!";
+        messagesCount = 1;
+        lastReadPos = lastWritePos = newLastWritePos;
+        goto create_array;
+    }
+    }
+    // Otherwise we ignore newLastWritePos, since we only have a copy of the buffer
+    // up to lastWritePos.
+
+    for (unsigned long long readPos = lastReadPos; readPos < lastWritePos; ) {
+        size_t messageLen = strlen(messageBufferCopy + (readPos % messageBufferSize));
+        if (messageLen != 0) {
+            readPos += messageLen + 1;
+            messagesCount++;
+        } else {
+            // Skip to the beginning of the buffer.
+            readPos = (readPos / messageBufferSize + 1) * messageBufferSize;
+        }
+    }
+    if (messagesCount == 0) {
+        lastReadPos = lastWritePos;
+        return result;
+    }
+
+create_array:
+    result = env->NewObjectArray(
+            messagesCount, env->FindClass("java/lang/String"), env->NewStringUTF(overrunMessage));
+    if (lastWritePos == lastReadPos) return result;
+
+    jsize arrayIndex = 0;
+    while (lastReadPos < lastWritePos) {
+        size_t wrappedReadPos = lastReadPos % messageBufferSize;
+        if (messageBufferCopy[wrappedReadPos] != '\0') {
+            jstring message = env->NewStringUTF(messageBufferCopy + wrappedReadPos);
+            env->SetObjectArrayElement(result, arrayIndex++, message);
+            lastReadPos += env->GetStringLength(message) + 1;
+            env->DeleteLocalRef(message);
+        } else {
+            // Skip to the beginning of the buffer.
+            lastReadPos = (lastReadPos / messageBufferSize + 1) * messageBufferSize;
+        }
+    }
+    return result;
+}
+
+} // namespace nativemididemo