Our problem:
We are capturing video and writing the data to a FileSystem, usually a NAS device. So we have sequential data to be written, and this code will be writing to multiple files on the same NAS - for 99% of the time it works, however occasionally this function will just hang.
I have this function that writes data to a file.
STDMETHODIMP FileWriter::Receive(LONG lStreamId, IStreamPacket* pPacket)
{
CMutexAutoLock lock(&m_csAccessControl);
HRESULT hr = S_OK;
// AddRef the packet to prevent loss
pPacket->AddRef();
if (m_hFile != INVALID_HANDLE_VALUE && pPacket) {
DWORD written = 0;
BYTE* pData = NULL;
LONG lLen = 0;
pPacket->get_Pointer(&pData);
pPacket->get_ActualDataLength(&lLen);
if (pData && lLen) {
WriteFile(m_hFile, pData, lLen, &written, NULL);
m_llPosition += written;
if (m_llPosition > m_llLength) {
m_llLength = m_llPosition;
}
}
m_xiPosition = (LONG)m_llPosition;
m_xiLength = (LONG)m_llLength;
m_xiLengthInMB = (LONG)(m_llLength/1024/1024);
}
// Release packet
pPacket->Release();
return hr;
}
Now, I cannot test this code easily, as it is used internally to a framework I am using. I do however have this code handy.
I have read online that the WriteFile() function can freeze the application, and this happens to us when the target file system is a NAS, but only very occasionally. When writing to the local HDD, this is never an issue. Unfortunately we require a very robust solution that we can write to a NAS without issue.
How could I modify this code so that the WriteFile() function always completes? I have read about using Overlapped IO, but I am not sure how I would go about this and if this is suitable.
Related
I'm trying to visualize a soundwave captured by WASAPI loopback but find that the packets I record do not form a smooth wave when put together.
My understanding of how the WASAPI capture client works is that when I call pCaptureClient->GetBuffer(&pData, &numFramesAvailable, &flags, NULL, NULL) the buffer pData is filled from the front with numFramesAvailable datapoints. Each datapoint is a float and they alternate by channel. Thus to get all available datapoints I should cast pData to a float pointer, and take the first channels * numFramesAvailable values. Once I release the buffer and call GetBuffer again it provides the next packet. I would assume that these packets would follow on from each other but it doesn't seem to be the case.
My guess is that either I'm making an incorrect assumption about the format of the audio data in pData or the capture client is either missing or overlapping frames. But have no idea how to check these.
To make the code below as brief as possible I've removed things like error status checking and cleanup.
Initialization of capture client:
const CLSID CLSID_MMDeviceEnumerator = __uuidof(MMDeviceEnumerator);
const IID IID_IMMDeviceEnumerator = __uuidof(IMMDeviceEnumerator);
const IID IID_IAudioClient = __uuidof(IAudioClient);
const IID IID_IAudioCaptureClient = __uuidof(IAudioCaptureClient);
pAudioClient = NULL;
IMMDeviceEnumerator * pDeviceEnumerator = NULL;
IMMDevice * pDeviceEndpoint = NULL;
IAudioClient *pAudioClient = NULL;
IAudioCaptureClient *pCaptureClient = NULL;
int channels;
// Initialize audio device endpoint
CoInitialize(nullptr);
CoCreateInstance(CLSID_MMDeviceEnumerator, NULL, CLSCTX_ALL, IID_IMMDeviceEnumerator, (void**)&pDeviceEnumerator );
pDeviceEnumerator ->GetDefaultAudioEndpoint(eRender, eConsole, &pDeviceEndpoint );
// init audio client
WAVEFORMATEX *pwfx = NULL;
REFERENCE_TIME hnsRequestedDuration = 10000000;
REFERENCE_TIME hnsActualDuration;
audio_device_endpoint->Activate(IID_IAudioClient, CLSCTX_ALL, NULL, (void**)&pAudioClient);
pAudioClient->GetMixFormat(&pwfx);
pAudioClient->Initialize(AUDCLNT_SHAREMODE_SHARED, AUDCLNT_STREAMFLAGS_LOOPBACK, hnsRequestedDuration, 0, pwfx, NULL);
channels = pwfx->nChannels;
pAudioClient->GetService(IID_IAudioCaptureClient, (void**)&pCaptureClient);
pAudioClient->Start(); // Start recording.
Capture of packets (note that std::mutex packet_buffer_mutex and vector<vector<float>> packet_bufferare already be defined and used by another thread to safely display the data):
UINT32 packetLength = 0;
BYTE *pData = NULL;
UINT32 numFramesAvailable;
DWORD flags;
int max_packets = 8;
std::unique_lock<std::mutex>write_guard(packet_buffer_mutex, std::defer_lock);
while (true) {
pCaptureClient->GetNextPacketSize(&packetLength);
while (packetLength != 0)
{
// Get the available data in the shared buffer.
pData = NULL;
pCaptureClient->GetBuffer(&pData, &numFramesAvailable, &flags, NULL, NULL);
if (flags & AUDCLNT_BUFFERFLAGS_SILENT)
{
pData = NULL; // Tell CopyData to write silence.
}
write_guard.lock();
if (packet_buffer.size() == max_packets) {
packet_buffer.pop_back();
}
if (pData) {
float * pfData = (float*)pData;
packet_buffer.emplace(packet_buffer.begin(), pfData, pfData + channels * numFramesAvailable);
} else {
packet_buffer.emplace(packet_buffer.begin());
}
write_guard.unlock();
hpCaptureClient->ReleaseBuffer(numFramesAvailable);
pCaptureClient->GetNextPacketSize(&packetLength);
}
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
I store the packets in a vector<vector<float>> (where each vector<float> is a packet) removing the last one and inserting the newest at the start so I can iterate over them in order.
Below is the result of a captured sinewave, plotting alternating values so it only represents a single channel. It is clear where the packets are being stitched together.
Something is playing a sine wave to Windows; you're recording the sine wave back in the audio loopback; and the sine wave you're getting back isn't really a sine wave.
You're almost certainly running into glitches. The most likely causes of glitching are:
Whatever is playing the sine wave to Windows isn't getting data to Windows in time, so the buffer is running dry.
Whatever is reading the loopback data out of Windows isn't reading the data in time, so the buffer is filling up.
Something is going wrong in between playing the sine wave to Windows and reading it back.
It is possible that more than one of these are happening.
The IAudioCaptureClient::GetBuffer call will tell you if you read the data too late. In particular it will set *pdwFlags so that the AUDCLNT_BUFFERFLAGS_DATA_DISCONTINUITY bit is set.
Looking at your code, I see you're doing the following things between the GetBuffer and the WriteBuffer:
Waiting on a lock
Sometimes doing something called "pop_back"
Doing something called "emplace"
I quote from the above-linked documentation:
Clients should avoid excessive delays between the GetBuffer call that acquires a packet and the ReleaseBuffer call that releases the packet. The implementation of the audio engine assumes that the GetBuffer call and the corresponding ReleaseBuffer call occur within the same buffer-processing period. Clients that delay releasing a packet for more than one period risk losing sample data.
In particular you should NEVER DO ANY OF THE FOLLOWING between GetBuffer and ReleaseBuffer because eventually they will cause a glitch:
Wait on a lock
Wait on any other operation
Read from or write to a file
Allocate memory
Instead, pre-allocate a bunch of memory before calling IAudioClient::Start. As each buffer arrives, write to this memory. On the side, have a regularly scheduled work item that takes written memory and writes it to disk or whatever you're doing with it.
The code below is required by my app to write disk sectors of external USB drives. It works on most Win10 PCs, but it's returning error 5 for permission denied on a couple PCs. I have exclusions created for both Windows Defender and Malwarebytes. There's nothing in the event viewer related to the failure. The read function works without error.
I tried adding calls to FSCTL_LOCK_VOLUME and FSCTL_DISMOUNT_VOLUME, but this doesn't help. Probably not needed anyway since I'm accessing the physical disk after it's been cleaned, and not any volumes.
Any idea what could cause this, or how to resolve?
Would be great to learn if there's any alternate methods of reading and writing disk sectors.
BOOL Partitioner::BlockWrite(wchar_t* devIdentifier, unsigned __int64 lngStartbyte, DWORD bytesToRead, BYTE* buf)
{
BOOL ret = FALSE;
HANDLE devHan = CreateFile(devIdentifier, GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
if (devHan != INVALID_HANDLE_VALUE)
{
// Seek to the starting block to write
LARGE_INTEGER startByte;
startByte.QuadPart = lngStartbyte;
SetFilePointer(devHan, startByte.LowPart, (long*)&startByte.HighPart, FILE_BEGIN);
// Write the data (this is where error 5 is returned)
DWORD bytesWritten = 0;
ret = WriteFile(devHan, buf, bytesToRead, &bytesWritten, NULL);
FlushFileBuffers(devHan);
CloseHandle(devHan);
}
else
{
ret = GetLastError();
wchar_t msg[PATH_BUFFER_SIZE] = {0};
swprintf_s(msg, WCSIZE_FULL(msg), L"Error= %d, byte= %llu", ret, lngStartbyte);
mLog->LogError(msg);
}
return ret;
}
I found the answer where I wasn't expecting. I thought this had to be something related to how the file handles were being opened. Instead, turning off Real-time protection in the Virus threat protection settings for Windows 10 caused the error 5s to go away. To resolve without disabling real-time protection, you need to add an allowed app exclusion for each of the installed EXEs.
You can do this in code by scripting PowerShell:
string script = "powershell -Command \"Add-MpPreference -ControlledFolderAccessAllowedApplications '" + GetAppPath() + "\\AppServer.exe" + "'";
Process.Start(new ProcessStartInfo() { FileName = "cmd.exe", Arguments = "/c " + script, CreateNoWindow = true, WindowStyle = ProcessWindowStyle.Hidden }).WaitForExit();
As per subject I'm trying to develop a simple piped parent/child program.
Main purpose of this program is to keep the child process alive and use std::cin and std::cout to communicate between parent/child processes.
On Linux all of this works quite well.
On Windows I've been following the example here and there's one peculiar difference with Linux: one has to invoke
CloseHandle(g_hChildStd_IN_Wr)
To write to the child pipe and flush it. This has the side effect to close the pipe, thus terminating my in-connection to the child process.
I've also tried to use FlushFileBuffers but it doesn't work.
Any idea how can I flush the buffer without having to close the anonymous pipe?
Below sources of both Parent and Child processes.
If the code of the parent process is basically the one in the example above:
// IN_Wr_ is initialized as below with bInheritHandle=TRUE
::CreatePipe(&IN_Rd_, &IN_Wr_, &saAttr, 0);
// and
::SetHandleInformation(IN_Wr_, HANDLE_FLAG_INHERIT, 0)
// When I spawn the child process I do
STARTUPINFO siStartInfo = {0};
siStartInfo.cb = sizeof(STARTUPINFO);
siStartInfo.hStdError = INVALID_HANDLE_VALUE;
siStartInfo.hStdOutput = OUT_Wr_;
siStartInfo.hStdInput = IN_Rd_;
siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
...
// then in order to write to std::cin
const DWORD reqSz = static_cast<DWORD>(std::strlen(request));
DWORD written = 0;
while(true) {
DWORD curWritten = 0;
if(!WriteFile(IN_Wr_, request + written, reqSz-written, &curWritten, NULL))
throw std::runtime_error("Error on WriteFile");
written += curWritten;
if(written == reqSz) {
// all written, done
break;
}
}
::FlushFileBuffers(IN_Wr_);
// only when I do this CloseHandle then the child process
// is able to read data
::CloseHandle(IN_Wr_);
this child code is a simple echo server, along the lines of:
buif[2048+1];
while(std::cin) {
std::cin.read(buf, 2048);
const auto rb = std::cin.gcount();
buf[rb] = '\0';
std::cout << buf << std::endl; // this does flush
}
Here's your problem:
std::cin.read(buf, 2048);
It's doing exactly what you've asked it to: waiting until it has read 2048 characters or reaches the end of file. You're not sending 2048 characters, so nothing happens until the server closes the pipe, which counts as the end of file in this context.
Instead, you should be using something like getline(s, 2048, '\0') which will stop reading when it sees a null character. (And, of course, you will need to modify the sender so that it writes that null character at the end of the string.)
Alternatively, you could use the native API: ReadFile has the semantics you seem to be wanting. Ideally you would use a message-mode pipe, which is designed precisely for this sort of use.
The article here might be helpful: https://support.microsoft.com/en-us/kb/190351. It has a section on flushing problems when printf is used to send data to the redirected pipe, which seems to be done in your case. The suggested solution is to use fflush(NULL) to flush the C run-time IO buffers.
It looks like the issue is a MSFT implementation of std::cin::read (and even fread(..., ..., ..., stdin)).
If instead of relying on:
// C++ API
while(std::cin) {
std::cin.read(buf, 2048);
...
// or also "C" API
int rb = 0;
while(0 < (rb = fread(buf, 2048, 1, stdin))) {
...
I do
// Low level Win32 "C" API
while(::ReadFile(hStdin, buf, 2048, &rb, 0)) {
...
// or also low level unix-like "C" API
int rb = 0;
while(0 < (rb = _read(0, buf, 2048))) {
...
The above example just works fine (funnily enough, the call to FlushFileBuffers is not even needed).
I want to check if the WriteFile function is done writing to UART so that i can call ReadFile on the same ComDev without causing an Exception.
It seems the WriteFile function can return before writing is done.
BOOL WriteCommBlock(HANDLE * pComDev, char *pBuffer , int BytesToWrite)
{
while(fComPortInUse){}
fComPortInUse = 1;
BOOL bWriteStat = 0;
DWORD BytesWritten = 0;
COMSTAT ComStat = {0};
OVERLAPPED osWrite = {0,0,0};
if(WriteFile(*pComDev,pBuffer,BytesToWrite,&BytesWritten,&osWrite) == FALSE)
{
short Errorcode = GetLastError();
if( Errorcode != ERROR_IO_PENDING )
short breakpoint = 5; // Error
Sleep(1000); // complete write operation TBD
fComPortInUse = 0;
return (FALSE);
}
fComPortInUse = 0;
return (TRUE);
}
I used Sleep(1000) as an workaround, but how can i wait for an appropriate time?
You can create a Event, store it in your overlapped structure and wait for it to be signalled. Like this (untested):
BOOL WriteCommBlock(HANDLE * pComDev, char *pBuffer , int BytesToWrite)
{
while(fComPortInUse){}
fComPortInUse = 1;
BOOL bWriteStat = 0;
DWORD BytesWritten = 0;
COMSTAT ComStat = {0};
OVERLAPPED osWrite = {0,0,0};
HANDLE hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (hEvent != NULL)
{
osWrite.hEvent = hEvent;
if(WriteFile(*pComDev,pBuffer,BytesToWrite,&BytesWritten,&osWrite) == FALSE)
{
short Errorcode = GetLastError();
if( Errorcode != ERROR_IO_PENDING )
short breakpoint = 5; // Error
WaitForSingleObject(hEvent, INFINITE);
fComPortInUse = 0;
return (FALSE);
}
CloseHandle(hEvent);
}
fComPortInUse = 0;
return (TRUE);
}
Note that depending on what else you are trying to do simply calling WaitForSingleObject() might not be the best idea. And neither might an INFINITE timeout.
Your problem is the incorrect use of the overlapped I/O, regardless to the UART or whatever underlying device.
The easiest (though not necessarily the most optimal) way to fix your code is to use an event to handle the I/O completion.
// ...
OVERLAPPED osWrite = {0,0,0};
osWrite.hEvent = CreateEvent(FALSE, NULL, NULL, FALSE);
if(WriteFile(*pComDev,pBuffer,BytesToWrite,&BytesWritten,&osWrite) == FALSE)
{
DWORD Errorcode = GetLastError();
// ensure it's ERROR_IO_PENDING
WaitForSingleObject(osWrite.hEvent, INFINITE);
}
CloseHandle(osWrite.hEvent);
Note however that the whole I/O is synchronous. It's handles by the OS in an asynchronous way, however your code doesn't go on until it's finished. If so, why do you use the overlapped I/O anyway?
One should use it to enable simultaneous processing of several I/Os (and other tasks) within the same thread. To do this correctly - you should allocate the OVERLAPPED structure on heap and use one of the available completion mechanisms: event, APC, completion port or etc. Your program flow logic should also be changed.
Since you didn't say that you need asynchronous I/O, you should try synchronous. It's easier. I think if you just pass a null pointer for the OVERLAPPED arg you get synchronous, blocking, I/O. Please see the example code I wrote in the "Windows C" section of this document:
http://www.pololu.com/docs/0J40/
Your Sleep(1000); is of no use, it will only execute after the writefile completes its operation.You have to wait till WriteFile is over.
if(WriteFile(*pComDev,pBuffer,BytesToWrite,&BytesWritten,&osWrite) == FALSE)
{}
You must be knowing that anything inside conditionals will only execute if the result is true.
And here the result is sent to the program after completion(whether complete or with error) of WriteFile routine.
OK, I missed the overlapped I/O OVL parameter in the read/write code, so It's just as well I only replied yesterday as a comment else I would be hammered with downvotes:(
The classic way of handling overlapped I/O is to have an _OVL struct as a data member of the buffer class that is issued in the overlapped read/write call. This makes it easy to have read and write calls loaded in at the same time, (or indeed, multiple read/write calls with separate buffer instances).
For COM posrts, I usually use an APC completion routine whose address is passed in the readFileEx/writeFileEx APIs. This leaves the hEvent field of the _OVL free to use to hold the instance pointer of the buffer so it's easy to cast it back inside the completion routine, (this means that each buffer class instance contains an _OVL memebr that contains an hEvent field that points to the buffer class instance - sounds a but weird, but works fine).
I'm writing a serial port software for Windows. To improve performance I'm trying to convert the routines to use asynchronous I/O. I have the code up and working fairly well, but I'm a semi-beginner at this, and I would like to improve the performance of the program further. During stress tests of the program (ie burst data to/from the port as fast as possible at high baudrate), the CPU load gets quite high.
If anyone out there has experience from asynchronous I/O and multi-threading in Windows, I'd be grateful if you could take a look at my program. I have two main concerns:
Is the asynchronous I/O implemented correctly? I found some fairly reliable source on the net suggesting that you can pass user data to the callback functions, by implementing your own OVERLAPPED struct with your own data at the end. This seems to be working just fine, but it does look a bit "hackish" to me. Also, the program's performance didn't improve all that much when I converted from synchronous/polled to asynchronous/callback, making me suspect I'm doing something wrong.
Is it sane to use STL std::deque for the FIFO data buffers? As the program is currently written, I only allow 1 byte of data to be received at a time, before it must be processed. Because I don't know how much data I will receive, it could be endless amounts. I assume this 1-byte-at-a-time will yield sluggish behaviour behind the lines of deque when it has to allocate data. And I don't trust deque to be thread-safe either (should I?).
If using STL deque isn't sane, are there any suggestions for a better data type to use? Static array-based circular ring buffer?
Any other feedback on the code is most welcome as well.
The serial routines are implemented so that I have a parent class called "Comport", which handles everything serial I/O related. From this class I inherit another class called "ThreadedComport", which is a multi-threaded version.
ThreadedComport class (relevant parts of it)
class ThreadedComport : public Comport
{
private:
HANDLE _hthread_port; /* thread handle */
HANDLE _hmutex_port; /* COM port access */
HANDLE _hmutex_send; /* send buffer access */
HANDLE _hmutex_rec; /* rec buffer access */
deque<uint8> _send_buf;
deque<uint8> _rec_buf;
uint16 _data_sent;
uint16 _data_received;
HANDLE _hevent_kill_thread;
HANDLE _hevent_open;
HANDLE _hevent_close;
HANDLE _hevent_write_done;
HANDLE _hevent_read_done;
HANDLE _hevent_ext_send; /* notifies external thread */
HANDLE _hevent_ext_receive; /* notifies external thread */
typedef struct
{
OVERLAPPED overlapped;
ThreadedComport* caller; /* add user data to struct */
} OVERLAPPED_overlap;
OVERLAPPED_overlap _send_overlapped;
OVERLAPPED_overlap _rec_overlapped;
uint8* _write_data;
uint8 _read_data;
DWORD _bytes_read;
static DWORD WINAPI _tranceiver_thread (LPVOID param);
void _send_data (void);
void _receive_data (void);
DWORD _wait_for_io (void);
static void WINAPI _send_callback (DWORD dwErrorCode,
DWORD dwNumberOfBytesTransfered,
LPOVERLAPPED lpOverlapped);
static void WINAPI _receive_callback (DWORD dwErrorCode,
DWORD dwNumberOfBytesTransfered,
LPOVERLAPPED lpOverlapped);
};
The main thread routine created through CreateThread():
DWORD WINAPI ThreadedComport::_tranceiver_thread (LPVOID param)
{
ThreadedComport* caller = (ThreadedComport*) param;
HANDLE handle_array [3] =
{
caller->_hevent_kill_thread, /* WAIT_OBJECT_0 */
caller->_hevent_open, /* WAIT_OBJECT_1 */
caller->_hevent_close /* WAIT_OBJECT_2 */
};
DWORD result;
do
{
/* wait for anything to happen */
result = WaitForMultipleObjects(3,
handle_array,
false, /* dont wait for all */
INFINITE);
if(result == WAIT_OBJECT_1 ) /* open? */
{
do /* while port is open, work */
{
caller->_send_data();
caller->_receive_data();
result = caller->_wait_for_io(); /* will wait for the same 3 as in handle_array above,
plus all read/write specific events */
} while (result != WAIT_OBJECT_0 && /* while not kill thread */
result != WAIT_OBJECT_2); /* while not close port */
}
else if(result == WAIT_OBJECT_2) /* close? */
{
; /* do nothing */
}
} while (result != WAIT_OBJECT_0); /* kill thread? */
return 0;
}
which in turn calls the following three functions:
void ThreadedComport::_send_data (void)
{
uint32 send_buf_size;
if(_send_buf.size() != 0) // anything to send?
{
WaitForSingleObject(_hmutex_port, INFINITE);
if(_is_open) // double-check port
{
bool result;
WaitForSingleObject(_hmutex_send, INFINITE);
_data_sent = 0;
send_buf_size = _send_buf.size();
if(send_buf_size > (uint32)_MAX_MESSAGE_LENGTH)
{
send_buf_size = _MAX_MESSAGE_LENGTH;
}
_write_data = new uint8 [send_buf_size];
for(uint32 i=0; i<send_buf_size; i++)
{
_write_data[i] = _send_buf.front();
_send_buf.pop_front();
}
_send_buf.clear();
ReleaseMutex(_hmutex_send);
result = WriteFileEx (_hcom, // handle to output file
(void*)_write_data, // pointer to input buffer
send_buf_size, // number of bytes to write
(LPOVERLAPPED)&_send_overlapped, // pointer to async. i/o data
(LPOVERLAPPED_COMPLETION_ROUTINE )&_send_callback);
SleepEx(INFINITE, true); // Allow callback to come
if(result == false)
{
// error handling here
}
} // if(_is_open)
ReleaseMutex(_hmutex_port);
}
else /* nothing to send */
{
SetEvent(_hevent_write_done); // Skip write
}
}
void ThreadedComport::_receive_data (void)
{
WaitForSingleObject(_hmutex_port, INFINITE);
if(_is_open)
{
BOOL result;
_bytes_read = 0;
result = ReadFileEx (_hcom, // handle to output file
(void*)&_read_data, // pointer to input buffer
1, // number of bytes to read
(OVERLAPPED*)&_rec_overlapped, // pointer to async. i/o data
(LPOVERLAPPED_COMPLETION_ROUTINE )&_receive_callback);
SleepEx(INFINITE, true); // Allow callback to come
if(result == FALSE)
{
DWORD last_error = GetLastError();
if(last_error == ERROR_OPERATION_ABORTED) // disconnected ?
{
close(); // close the port
}
}
}
ReleaseMutex(_hmutex_port);
}
DWORD ThreadedComport::_wait_for_io (void)
{
DWORD result;
bool is_write_done = false;
bool is_read_done = false;
HANDLE handle_array [5] =
{
_hevent_kill_thread,
_hevent_open,
_hevent_close,
_hevent_write_done,
_hevent_read_done
};
do /* COM port message pump running until sending / receiving is done */
{
result = WaitForMultipleObjects(5,
handle_array,
false, /* dont wait for all */
INFINITE);
if(result <= WAIT_OBJECT_2)
{
break; /* abort */
}
else if(result == WAIT_OBJECT_3) /* write done */
{
is_write_done = true;
SetEvent(_hevent_ext_send);
}
else if(result == WAIT_OBJECT_4) /* read done */
{
is_read_done = true;
if(_bytes_read > 0)
{
uint32 errors = 0;
WaitForSingleObject(_hmutex_rec, INFINITE);
_rec_buf.push_back((uint8)_read_data);
_data_received += _bytes_read;
while((uint16)_rec_buf.size() > _MAX_MESSAGE_LENGTH)
{
_rec_buf.pop_front();
}
ReleaseMutex(_hmutex_rec);
_bytes_read = 0;
ClearCommError(_hcom, &errors, NULL);
SetEvent(_hevent_ext_receive);
}
}
} while(!is_write_done || !is_read_done);
return result;
}
Asynchronous I/O callback functions:
void WINAPI ThreadedComport::_send_callback (DWORD dwErrorCode,
DWORD dwNumberOfBytesTransfered,
LPOVERLAPPED lpOverlapped)
{
ThreadedComport* _this = ((OVERLAPPED_overlap*)lpOverlapped)->caller;
if(dwErrorCode == 0) // no errors
{
if(dwNumberOfBytesTransfered > 0)
{
_this->_data_sent = dwNumberOfBytesTransfered;
}
}
delete [] _this->_write_data; /* always clean this up */
SetEvent(lpOverlapped->hEvent);
}
void WINAPI ThreadedComport::_receive_callback (DWORD dwErrorCode,
DWORD dwNumberOfBytesTransfered,
LPOVERLAPPED lpOverlapped)
{
if(dwErrorCode == 0) // no errors
{
if(dwNumberOfBytesTransfered > 0)
{
ThreadedComport* _this = ((OVERLAPPED_overlap*)lpOverlapped)->caller;
_this->_bytes_read = dwNumberOfBytesTransfered;
}
}
SetEvent(lpOverlapped->hEvent);
}
The first question is simple. The method is not hackish; you own the OVERLAPPED memory and everything that follows it. This is best described by Raymond Chen: http://blogs.msdn.com/b/oldnewthing/archive/2010/12/17/10106259.aspx
You would only expect a performance improvement if you've got better things to while waiting for the I/O to complete. If all you do is SleepEx, you'll only see CPU% go down. The clue is in the name "overlapped" - it allows you to overlap calculations and I/O.
std::deque<unsigned char> can handle FIFO data without big problems. It will probably recycle 4KB chunks (precise number determined by extensive profiling, all done for you).
[edit]
I've looked into your code a bit further, and it seems the code is needlessly complex. For starters, one of the main benefits of asynchronous I/O is that you don't need all that thread stuff. Threads allow you to use more cores, but you're dealing with a slow I/O device. Even a single core is sufficient, if it doesn't spend all its time waiting. And that's precisely what overlapped I/O is for. You just dedicate one thread to all I/O work for the port. Since it's the only thread, it doesn't need a mutex to access that port.
OTOH, you would want a mutex around the deque<uint8> objects since the producer/consumer threads aren't the same as the comport thread.
I don't see any reason for using asynchronous I/O in a project like this. Asynchronous I/O is good when you're handling a large number of sockets or have work to do while waiting for data, but as far as I can tell, you're only dealing with a single socket and not doing any work in between.
Also, just for the sake of knowledge, you would normally use an I/O completion port to handle your asynchronous I/O. I'm not sure if there are any situations where using an I/O completion port has a negative impact on performance.
But yes, your asynchronous I/O usage looks okay. Implementing your own OVERLAPPED struct does look like a hack, but it is correct; there's no other way to associate your own data with the completion.
Boost also has a circular buffer implementation, though I'm not sure if it's thread safe. None of the standard library containers are thread safe, though.
I think that your code has suboptimal design.
You are sharing too many data structures with too many threads, I guess. I think that you should put all handling of the serial device IO for one port into a single thread and put a synchronized command/data queue between the IO thread and all client threads. Have the IO thread watch out for commands/data in the queue.
You seem to be allocating and freeing some buffers for each sent event. Avoid that. If you keep all the IO in a single thread, you can reuse a single buffer. You are limiting the size of the message anyway, you can just pre-allocate a single big enough buffer.
Putting the bytes that you want to send into a std::deque is suboptimal. You have to serialize them into a continuous memory block for the WriteFile(). Instead, if you use some sort of commdand/data queue between one IO thread and other threads, you can have the client threads provide the continuous chunk of memory at once.
Reading 1 byte at a time seem silly, too. Unless it does not work for serial devices, you could provide large enough buffer to ReadFileEx(). It returns how many bytes it has actually managed to read. It should not block, AFAIK, unless of course I am wrong.
You are waiting for the overlapped IO to finish using the SleepEx() invocation. What is the point of the overlapped IO then if you are just ending up being synchronous?