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/*
* 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
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