SiddiqSoft.RWLEnvelope 1.0.0

RWLEnvelope : A simple read-writer lock wrapper for modern C++

Objective

• Avoid re-implementing the rw-lock; standard C++ (since C++14) has a good reader-writer lock implementation.
• Provide a simple, convenience layer atop the underlying std::unique_lock and std::shared_lock access to some type.

WE DO NOT IMPLEMENT a read-writer lock, rather we provide a simple pattern where the most frequent use of the underlying facility is in a neat package.

Requirements

You must be able to use <shared_mutex> and <mutex>

The build and tests are for Visual Studio 2019 under x64.

Usage

• Use the nuget SiddiqSoft.RWLEnvelope
• Copy paste..whatever works.
• Two methods: -- Observer/mutator model with callback and custom return

#include "gtest/gtest.h"

#include "nlohmann/json.hpp"
#include "../src/RWLEnvelope.hpp"


TEST(examples, WithCallbacks)
{
	siddiqsoft::RWLEnvelope<nlohmann::json> docl({{"foo", "bar"}, {"few", "lar"}});

	// Check we have pre-change value..
	EXPECT_EQ("bar", docl.observe<std::string>([](const auto& doc) { return doc.value("foo", ""); }));

	// Modify the item
	docl.mutate<void>([](auto& doc) { doc["foo"] = "bare"; });

	// Check we have pre-change value.. Note that here we return a boolean to avoid data copy
	EXPECT_TRUE(docl.observe<bool>([](const auto& doc) { return doc.value("foo", "").find("bare") == 0; }));

	// Check to make sure that the statistics match
	auto info = nlohmann::json(docl);
	EXPECT_EQ(1, info.value("readWriteActions", 0));
}


TEST(examples, WithDirectLocks)
{
	siddiqsoft::RWLEnvelope<nlohmann::json> docl({{"foo", "bar"}, {"few", "lar"}});

	// Check we have pre-change value..
	if (const auto& [doc, rl] = docl.readLock(); rl) { EXPECT_EQ("bar", doc.value("foo", "")); }

	// Modify the item
	if (auto& [doc, wl] = docl.writeLock(); wl) { doc["foo"] = "bare"; };

	// Check we have pre-change value.. Note that here we return a boolean to avoid data copy
	if (const auto& [doc, rl] = docl.readLock(); rl) { EXPECT_TRUE(doc.value("foo", "").find("bare") == 0); }
}

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