void AsyncLogging::threadFunc()
{
assert(running_ == true);
latch_.countDown();
LogFile output(basename_, rollSize_, false);
BufferPtr newBuffer1(new Buffer);
BufferPtr newBuffer2(new Buffer);
newBuffer1->bzero();
newBuffer2->bzero();
BufferVector buffersToWrite;
buffersToWrite.reserve(16);
while(running_)
{
assert(newBuffer1 && newBuffer1->length() == 0);
assert(newBuffer2 && newBuffer2->length() == 0);
assert(buffersToWrite.empty());
{
dbdky::MutexLockGuard lock(mutex_);
if (buffers_.empty())
{
cond_.waitForSeconds(flushInterval_);
}
buffers_.push_back(currentBuffer_.release());
currentBuffer_ = boost::ptr_container::move(newBuffer1);
buffersToWrite.swap(buffers_);
if (!nextBuffer_)
{
nextBuffer_ = boost::ptr_container::move(newBuffer2);
}
}
assert(!buffersToWrite.empty());
if (buffersToWrite.size() > 25)
{
char buf[256];
snprintf(buf, sizeof buf, "Dropped log messages at %s, %zd larger buffers\n", Timestamp::now().toFormattedString().c_str(),
buffersToWrite.size() - 2);
fputs(buf, stderr);
output.append(buf, static_cast<int>(strlen(buf)));
buffersToWrite.erase(buffersToWrite.begin() + 2, buffersToWrite.end());
}
for (size_t i = 0; i < buffersToWrite.size(); i++)
{
output.append(buffersToWrite[i].data(), buffersToWrite[i].length());
}
if (buffersToWrite.size() > 2)
{
buffersToWrite.resize(2);
}
if (!newBuffer1)
{
assert(!buffersToWrite.empty());
newBuffer1 = buffersToWrite.pop_back();
newBuffer1->reset();
}
if (!newBuffer2)
{
assert(!buffersToWrite.empty());
newBuffer2 = buffersToWrite.pop_back();
newBuffer2->reset();
}
buffersToWrite.clear();
output.flush();
}
output.flush();
}
void AsyncLogging::threadFunc()
{
assert(running_ == true);
latch_.countDown();
LogFile output(basename_, rollSize_, false); //Important 这里的传入的threadsafe为false，为什么，因为异步本身就保证了线程安全
BufferPtr newBuffer1(new Buffer);
BufferPtr newBuffer2(new Buffer);
newBuffer1->bzeroinit();
newBuffer2->bzeroinit();
BufferVector buffersToWrite;
buffersToWrite.reserve(16);
while (running_)
{
{
lock_guard_t lock(mutex_); //用来和生产者互斥
if (buffers_.empty()) //unsual usage,没有使用while循环
{
cond_.wait(flushInterval_ * 1000);//flushInterval_是seconds
}
//执行到这里有2个条件：其一是超时，其二是写满了一个或多个buffer
buffers_.push_back(currentBuffer_.release());//移动，而非复制 ,release类似std::auto_ptr的release, 返回包含指针的地址，并将包含指针设为NUll
currentBuffer_ = boost::ptr_container::move(newBuffer1);//移动，而非复制
buffersToWrite.swap(buffers_);//内部指针交换，而非复制 ,交换后，可在临界区外安全地访问buffersToWrite，将其中的日志数据写入文件
if (!nextBuffer_)//临界区最终干的一件事情是用newBuffer2替换nextBuffer_,这样前端始终有一个备用buffer,nextbuffer_减少前端分配内存的概率
{
nextBuffer_ = boost::ptr_container::move(newBuffer2);
}
}
assert(!buffersToWrite.empty());
if (buffersToWrite.size() > 25)//日志堆积，直接丢掉
{
char buf[256];
snprintf(buf, sizeof buf, "Dropped log messages at %s, %zd larger buffers\n",
Timestamp::now().toFormattedString().c_str(),
buffersToWrite.size() - 2);
fputs(buf, stderr);
output.append(buf, static_cast<int>(strlen(buf)));
buffersToWrite.erase(buffersToWrite.begin() + 2, buffersToWrite.end());
}
for (size_t i = 0; i < buffersToWrite.size(); i++)
{
// FIXME: use unbuffered stdio FILE ? or use ::writev ?
output.append(buffersToWrite[i].data(), buffersToWrite[i].length());
}
if (buffersToWrite.size() > 2)
{
// drop non-bzero-ed buffers, avoid trashing
buffersToWrite.resize(2);
}
if (!newBuffer1)
{
assert(!buffersToWrite.empty());
newBuffer1 = buffersToWrite.pop_back();
newBuffer1->reset(); //将buffer的指针指向头部
}
if (!newBuffer2)
{
assert(!buffersToWrite.empty());
newBuffer2 = buffersToWrite.pop_back();
newBuffer2->reset();
}
buffersToWrite.clear();
output.flush();
}
output.flush();
}