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Make it possible to check that an implementation is supported at runtime (#1197)

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* Make it possible to check that an implementation is supported at runtime.

* add CI fuzzing on arm 64 bit

This adds fuzzing on drone.io arm64

For some reason, leak detection had to be disabled. If it is enabled, the fuzzer falsely reports a crash at the end of fuzzing.

Closes: #1188

* Guarding the implementation accesses.

* Better doc.

* Updating cxxopts.

* Make it possible to check that an implementation is supported at runtime.

* Guarding the implementation accesses.

* Better doc.

* Updating cxxopts.

* We need to accomodate cxxopts

Co-authored-by: Paul Dreik <github@pauldreik.se>
This commit is contained in:
Daniel Lemire
2020-10-02 11:04:51 -04:00
committed by GitHub
parent e06ddea784
commit 9865bb6904
19 changed files with 159 additions and 25 deletions
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doc/implementation-selection.md
+36
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@@ -6,6 +6,7 @@ CPU Architecture-Specific Implementations
* [Inspecting the Detected Implementation](#inspecting-the-detected-implementation)
* [Querying Available Implementations](#querying-available-implementations)
* [Manually Selecting the Implementation](#manually-selecting-the-implementation)
* [Checking that an Implementation can Run on your System](#checking-that-an-implementation-can-run-on-your-system)
Overview
--------
@@ -70,6 +71,14 @@ And look them up by name:
```c++
cout << simdjson::available_implementations["fallback"]->description() << endl;
```
Though the fallback implementation should always be available, others might be missing. When
an implementation is not available, the bracket call `simdjson::available_implementations[name]`
will return the null pointer.
The available implementations have been compiled but may not necessarily be run safely on your system
see [Checking that an Implementation can Run on your System](#checking-that-an-implementation-can-run-on-your-system).
Manually Selecting the Implementation
-------------------------------------
@@ -81,3 +90,30 @@ can select the CPU architecture yourself:
// Use the fallback implementation, even though my machine is fast enough for anything
simdjson::active_implementation = simdjson::available_implementations["fallback"];
```
You are responsible for ensuring that the requirements of the selected implementation match your current system.
Furthermore, you should check that the implementation is available before setting it to `simdjson::active_implementation`
by comparing it with the null pointer.
```c++
auto my_implementation = simdjson::available_implementations["haswell"];
if(! my_implementation) { exit(1); }
if(! my_implementation->supported_by_runtime_system()) { exit(1); }
simdjson::active_implementation = my_implementation;
```
Checking that an Implementation can Run on your System
-------------------------------------
You should call `supported_by_runtime_system()` to compare the processor's features with the need of the implementation.
```c++
for (auto implementation : simdjson::available_implementations) {
if(implementation->supported_by_runtime_system()) {
cout << implementation->name() << ": " << implementation->description() << endl;
}
}
```
The call to `supported_by_runtime_system()` maybe relatively expensive. Do not call `supported_by_runtime_system()` each
time you parse a JSON input (for example). It is meant to be called a handful of times at most in the life of a program.