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Add missing mutex lock. #37

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igorpeshansky merged 1 commit into from
Oct 16, 2017
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Add missing mutex lock. #37

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1 change: 1 addition & 0 deletions src/api_server.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,7 @@ void MetadataApiServer::Handler::operator()(const HttpServer::request& request,
<< " body: " << request.body;
if (request.method == "GET" && request.destination.find(kPrefix) == 0) {
std::string id = request.destination.substr(kPrefix.size());
std::lock_guard<std::mutex> lock(agent_.mu_);
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@dhrupadb dhrupadb Oct 16, 2017

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Just curious -- are there more than 1 read threads?

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@igorpeshansky igorpeshansky Oct 16, 2017

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Yes, the number of server threads is specified in the config (MetadataApiNumThreads). But it's enough to have 1 read thread and 1 write thread to trigger the race condition.

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@dhrupadb dhrupadb Oct 16, 2017

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SGTM. I only ask because read threads should not have to block other read threads. Its only when writes happen or attempts to read when a write is in progress that the mutex actually comes in. Probably a micro-optimization to be deferred for later.

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@igorpeshansky igorpeshansky Oct 16, 2017

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Very true. Will fix this later (I'm not too happy with the direct access to the agent's fields, including the mutex, from a friend class anyway).

const auto result = agent_.resource_map_.find(id);
if (result == agent_.resource_map_.end()) {
// TODO: This could be considered log spam.
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