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[QC-1038] fix Race condition in Service Discovery #2024

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merged 4 commits into from
Nov 2, 2023
Merged

[QC-1038] fix Race condition in Service Discovery #2024

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76412c5
[QC-1038] fix Race condition in Service Discovery
Barthelemy Nov 1, 2023
7d84782
format
Barthelemy Nov 1, 2023
a3b31a6
add missing include
Barthelemy Nov 1, 2023
b9dc161
add missing include
Barthelemy Nov 2, 2023
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5 changes: 5 additions & 0 deletions Framework/include/QualityControl/ServiceDiscovery.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,8 @@
#include <memory>
#include <string>
#include <thread>
#include <mutex>
#include <condition_variable>

typedef void CURL;

Expand Down Expand Up @@ -65,6 +67,9 @@ class ServiceDiscovery
const std::string mId; ///< Instance (service) ID
std::string mHealthUrl; ///< hostname of health check endpoint
size_t mHealthPort; ///< Port of the health check endpoint
std::mutex mHealthPortMutex; ///< Mutex for the port
std::condition_variable mHealthPortCV; ///< Condition varaible for the port
std::atomic<bool> mHealthPortAssigned; ///< Port of the health check is ready.
std::thread mHealthThread; ///< Health check thread
std::atomic<bool> mThreadRunning; ///< Health check thread running flag

Expand Down
18 changes: 15 additions & 3 deletions Framework/src/ServiceDiscovery.cxx
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Expand Up @@ -38,6 +38,7 @@ ServiceDiscovery::ServiceDiscovery(const std::string& url, const std::string& na
: curlHandle(initCurl(), &ServiceDiscovery::deleteCurl), mConsulUrl(url), mName(name), mId(id), mHealthUrl(healthEndUrl)
{
mHealthUrl = mHealthUrl.empty() ? boost::asio::ip::host_name() : mHealthUrl;
mHealthPortAssigned = false;

mHealthThread = std::thread([=] {
#ifdef __linux__
Expand Down Expand Up @@ -96,6 +97,11 @@ bool ServiceDiscovery::_register(const std::string& objects)
check.put("Name", "Health check " + mId);
check.put("Interval", "5s");
check.put("DeregisterCriticalServiceAfter", "1m");
// Wait until port is set by the thread
{
std::unique_lock<std::mutex> lk(mHealthPortMutex);
mHealthPortCV.wait(lk, [this] { return mHealthPortAssigned == true; });
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Maybe I misunderstood how condition_variable works, but won't it block the second time you call _register? I am not sure if it requires the other thread to call notify_one() for each wait.

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OK, I wrote a little reproducer and it seems it my concern is not valid, it seems that notify_one() unblocks the main thread forever, as long as the predicate is provided in wait.

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as you noted, as long as the predicate is true, it will let the main thread continue.

}
check.put("TCP", mHealthUrl + ":" + std::to_string(mHealthPort));
checks.push_back(std::make_pair("", check));

Expand Down Expand Up @@ -151,12 +157,18 @@ void ServiceDiscovery::runHealthServer()
ILOG(Debug, Trace) << "ServiceDiscovery::runHealthServer - cound not bind to " << port << ENDM;
continue; // try the next one
}
// if we reach this point it means that we could bind
mHealthPort = port;
ILOG(Debug, Devel) << "ServiceDiscovery selected port: " << mHealthPort << ENDM;
break;
}

// assign the port and unblock the main thread (we got a port or we failed)
{
ILOG(Debug, Devel) << "ServiceDiscovery selected port: " << mHealthPort << ENDM;
std::lock_guard<std::mutex> lk(mHealthPortMutex);
mHealthPort = port;
mHealthPortAssigned = true;
}
mHealthPortCV.notify_one();

if (cycle == rangeLength) {
ILOG(Error, Support) << "Could not find a free port for the ServiceDiscovery, aborting the ServiceDiscovery health check" << ENDM;
return;
Expand Down
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