Currently in the entire C API of WPILib we have ~8 different ways of handling strings. The C API actually isn't built for pure C callers (We don't actually have any of those). Instead, they're built for interop between languages like LabVIEW and C# which can talk to C API's directly.
For output parameters, the choice was fairly obvious. An output struct containing a const string pointer and a length makes the most sense. Its easy to use these from most other languages, and doesn't require special null termination handling. Freeing these is also easy, as if you ever receive one of these string structures, theres just a single function call to free it.
Input parameters are a bit more complex. To be used from pure C, and from LabVIEW, a null terminated string is the best in most cases. However, null terminated strings in general have a lot of downsides. Additionally, from LabVIEW there are other considerations around encoding that having a wrapper struct helps make a bit easier. From a language like C#, a wrapper struct is by far the easiest, as custom marshalling can make it trivial to marshal both UTF8 and UTF16 strings down.
The final consideration is its nice to have an identical concept for both input and output. It makes the rules fairly easy to understand.
WPILib will not have any APIs that manipulate a string allocated externally. This means WPI_String can be const, as across the boundary it is always const.
If a WPILib API takes a const WPI_String*, WPILib will not manipulate or attempt to free that string, and that string is treated as an input. It is up to the caller to handle that memory, WPILib will never hold onto that memory longer than the call.
If a WPILib API takes a WPI_String*, that string is an output. WPILib will allocate that API with WPI_AllocateString(), fill in the string, and return to the caller. When the caller is done with the string, they must free it with WPI_FreeString().
If an output struct contains a WPI_String member, that member is considered read only, and should not be explicitly freed. The caller should call the free function for that struct.
If an array of WPI_Strings are returned, each individual string is considered read only, and should not be explicitly freed. The free function for that array should be called by the caller.
If an input struct containing a WPI_String, or an input array of WPI_Strings is passed to WPILib, the individual strings will not be manipulated or freed by WPILib, and the caller owns and should free that memory.
Callbacks also follow these rules. The most common is a callback either getting passed a const WPI_String* or a struct containing a WPI_String. In both of these cases, the callback target should consider these strings read only, and not attempt to free them or manipulate them.
The default state for the DS in the simulated HAL is changed to disconnected.
The FMS view is now only editable in DS disconnected state.
This enables more robot and field-like testing of robot code, as the
alliance color and other parameters start in invalid states and are
only set when the DS connects.
During HAL_Initialize, wait up to 100ms for a DS packet to be received. Then in RobotBase, right after calling HAL_Initialize, call each language's RefreshData function to force a high level DS update. If the DS is connected, will get joystick data. If there is no data, nothing different will happen, but in that case there's no joysticks anyway.
Using an atomic here means we are never going against a lock that is touchable from user code. That should make reading the DS data from the DS callback even safer.
The current DS thread model has some pretty major issues. It makes it difficult to know if all data is from the same remote packet, and if the data changes while the robot loop is running. Additionally, the DS thread is used for a few other things (MotorSafety and State Tracking for EducationalRobot). This also makes sim difficult, as user code has to wait for the thread to know it has new data.
This change completely rethinks how threading works in the driver station model.
First, the DS HAL system receives a new data callback, either from Netcomm or DriverStationSim. Inside the context of this callback, all the low latency data is read and put into a cache. Doing some investigation on the robot side, this is perfectly safe to do, and also ensures a ds packet will not be parsed before we finish reading the current packet data.
After all data is read, the cache is swapped with a 2nd buffer. This buffer just stores the data, none of the HAL DS calls read from this buffer. An event is then fired, stating there is new data ready to go.
Robot code calls HAL_UpdateDSData(). This swaps the 2nd buffer with a 3rd buffer, which always contains the current data. This data will not be updated until HAL_UpdateDSData is called again. Which solves the state problem.
The high level driver station classes have. an updateData() call, which calls HAL_UpdateDSData, and then update button state variables, then data log and update the NT FMS data table (Java also caches across the JNI boundary here, but that could trivially be removed). An extra event provider is provided, allowing other threads to know when this call has been completed.
IterativeRobotBase calls DS.updateData() at the beginning of each loop, and only once per loop. This means all commands will always have the same state.
All of this means there is no longer a DS thread. Everything happens synchronously. This means Sim and testing is easier, as you can just call DriverStationSim.NotifyNewData(), and then DriverStation.UpdateData(), and you can guarantee that all the DriverStation.*** data is up to date.
As for Motor Safety and Educational Robot State Handling, those can all be handled by their own threads. The Educational Thread only needs to run under EducationalRobot, and MotorSafety will only be started if there is a motor safety object enabled.
- Twine, StringRef, Format, and NativeFormatting have been removed
- Logging now uses fmtlib style formatting
- Nearly all uses of wpi::outs/errs have been replaced with fmt::print() or
std::puts()/std::fputs() (for unformatted strings).
- A wpi/fmt/raw_ostream.h header has been added to enable
fmt::print() with wpi::raw_ostream
This makes code easier to read and more consistent between C++ and Java.
Also update clang-format settings to always add a line break (even if no braces are used).
Remove WaitForCachedData as it's no longer required.
Also properly handle caching / transition detection logic that occurs at the
WPILib level.
This also changes DriverStation::IsNewControlData() to check for WPILib-level
caching instead of wrapping the HAL function.
Also move some things in HAL for consistency.
WAS:
C++:
- C APIs: #include "mockdata/AccelerometerData.h"
- User side class: #include "simulation/AccelerometerSim.h"
Java:
- JNI APIs: hal.sim.mockdata.AccelerometerData (and a few classes in hal.sim)
- User side classes: hal.sim.AccelerometerSim
IS:
C++:
- C APIs: #include "hal/simulation/AccelerometerData.h"
- C++ class: #include "frc/simulation/AccelerometerSim.h"
Java:
- JNI APIs: hal.simulation.AccelerometerData
- User side class: wpilibj.simulation.AccelerometerSim
std::scoped_lock was introduced in C++17 and is strictly better than
std::lock_guard as it supports locking any number of mutexes safely.
It's also easier to use than std::lock for locking multiple mutexes at
once.
The next line adds a null terminator, but it's cleaner to just do a
std::memcpy() since the code already assumes a null terminator exists in
the source string.
This makes callback registration completely thread safe.
This patch also uses templates and macros to dramatically reduce the amount of
manual boilerplate.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
Also switch eventName and gameSpecificData to fixed 64-byte arrays to avoid mallocs and
extra NetComm calls. This behavior matches 2018 LabView.
The DS caching is kept in Java to avoid JNI and/or massive amounts of allocations.
This does not increase latency because Java still only hits NetComm once.
Moving the DS caching benefits all languages other than Java, because it avoids the need
for individual implementations. If caching is ever added to NetComm, it will then only be
necessary to remove it from the HAL and Java rather than all languages.
Also fix the return type of HAL_IsNewControlData() and HAL_MatchType's type.
Since UsageReporting is intended to be namespaced, it is hidden when this is being used in C.
Fixes: #476Closes: #535
Ref: #1122
During shared library loading, a different libLLVM can be pulled in, causing
llvm symbols from dependent libraries to resolve to that library instead of
this one. This has been seen in the wild with the Mesa OpenGL implementation
in JavaFX applications (see wpilibsuite/shuffleboard#361).
This is clearly a very breaking change. For some level of backwards
compatibility, a namespace alias from llvm to wpi is performed in the "llvm"
headers. Unfortunately, forward declarations of llvm classes will still break,
but compilers seem to generate clear error messages in those cases
("namespace alias 'llvm' not allowed here, assuming 'wpi'").
This change also moves all the wpiutil headers to a single "wpi" subdirectory
from the previously split "llvm", "support", "tcpsockets", and "udpsockets".
Shim headers will be added for backwards compatibility in a later commit.
* Removed hal::priority_condition_variable
* Replaced uses of priority mutexes with std::mutex and std::recursive_mutex
This allowed replacing a use of std::condition_variable_any with
std::condition_variable.
* Replaced all uses of std::recursive_mutex with std::mutex equivalents
