Pull #54 breaks the Windows version of dump1090 due to a bug in the
inet_aton() windows function.
1) Fix the bug in the windows inet_aton()
2) Modify the command line code to strdup() the command line string.
3) Leave the Modes.net_bind_address pointer NULL if no command line
specified
Mostly refactoring the common code that was duplicated
between the different output types so that there aren't
many copies floating around.
This introduces "struct net_writer" to store the state of a
particular type of output service - buffers, time of last write,
connection count etc. prepareWrite() / completeWrite() give access
to the buffer and handle the actual writes and flushing when needed.
Heartbeat and time-based flushing move into a generic periodic-work
function.
Update the SBS output code to use the new infrastructure. This makes
a big different to CPU use when under load.
When we read from some client A, we may end up forwarding a message to other
clients. If we forward to some client B and there is a write error, then
we close B and remove it from the client list. However, if before this happened
A->next == B, then the read loop will still be holding on to a pointer to B,
and we crash.
As it's unpredictable what clients could be closed at what point, the simplest
approach is to retain closed clients in the list until we are at a point where
we know there are no stray pointers on stack, and only then modify the list.
This also simplifies anything that has to loop over clients, as it doesn't need
to worry about the current client being freed under it.
If we demodulate a message in 2.4MHz mode and it has a bad, uncorrectable CRC,
and --phase-enhance is on, then retry with the other possible phases until
we get a good CRC or run out of phases to try.
This is very expensive in AGC mode (lots of candidates that are not real
messages) but relatively cheap otherwise. It yields another 10% messages.
Also factor out some common stats code to avoid lots more copy/paste.
When replaying recordings, the read files are binary, so the file open
needs to reflect this so that spurious end of file characters aren't
misinterpreted.
This disables most decoding of the contents of Mode S messages, aircraft tracking, and some output modes that depend on them.
It's intended for edge receivers that just forward to a central hub rather than processing data locally.
A few minor additions and bug fixes as detailed below
1) Additional command line option "--net-buffer <n>" to specify the TCP
output buffer size. Default is n=0, which is 64Kb. Specify a value of n
to increase the buffer size according to Size = 64Kb * 2^n, so an n of
1 = 128Kb, n=2 is 256Kb etc. n is limited to 7, so the max size is 8Mb.
This option may assist if you have a high number of aircraft being
received, and an unreliable network connection, or if the receiving end
can be busy for an extended time.
2) Bug fix in ppup1090 which prevented the uploading of valid
ModeA/Squawk codes
3) Bug fix per Markus Grab's commit.
Make the modifications necessary to compile dump1090 for WinXP, Win7 and
hopefully Win8.
The files can be compiled using M$ Visual Studio/C++ 6.0. Due to various
licensing issues, I haven't included the libraries or DLLs. You will
need to locate pthreadVC2.lib and rtlsdr.lib to link the file, install
the zadig drivers to support the dongle, and locate libusb-1.0.dll,
msvcr100.dll, pthreadVC2.dll and rtlsdr.dll.
dump1090.exe will not run on any Windows version prior to XP SP2,
because msvcr100.dll imports several functions from the Windows kernel
that are not available on earlier versions. This means dump1090 won't
work on Win2K.
The major change to the code relates to file handles. The original code
assumes Linux behaviour in that handles are allocated from 0
sequentially upwards. However Windows handles are allocated pseudo
randomly, and handle numbers greater than 1024 would break the code. The
code has therefore been modified to use a linked list of connection
structures, rather than a static array limited to 1024 entries.
Some users have reported issues where the TCP link to dump1090 can be
lost at times of low traffic density - typically in the middle of the
night. One possible reason for this is that some routers drop the link
if there is no traffic for a predetermined period.
To try and resolve this, dump1090 now sends a 'null' packet consisting
of 7 "0x00" bytes approximately once a minute if there is no real
received traffic during this time. This packet should be discarded by
the application receiving the dump1090 because it will have an invalid
checksum, and ICAO address 0x000000 is also invalid. However, this null
packet should be enough to keep routers alive.
The Mutex on the RTL data reader thread does not "force" the data
processing thread to execute. Therefore, if the processor is busy, it is
possible for a second RTL callback to occur before the data from the
first has been processed. This will cause the loss of the first data,
but worse, it will cause a slip in the timestamp. This upsets Beamfinder
and MLAT operation in PlanePlotter.
To solve this, keep a Fifo buffer which is filled by the callback
thread, and emptied by the data processing thread. The fifo is the same
size as the number of buffers requested in the call to
rtlsdr_read_async().
Note - we only put the value of the pointer supplied in the callback
into the fifo. We do not attempt to cache the data in the buffer pointed
to by the pointer. This would require us to memcopy() 2Mbytes per
second, which we don't want to do if we don't have to because it will
only make the processor loading worse. Instead, we assume that the data
in the buffer will remain valid after the callback returns, at least
until it is overwritten by new data.
It is still possible for us to lose data if we can't process it quickly
enough. However, we can now detect this loss of data when the fifo is
almost full, and correct the timestamp for the lost block/blocks.
