ClickHouse/dbms/src/Common/RWLock.cpp

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#include "RWLock.h"
#include <Common/Stopwatch.h>
#include <Common/Exception.h>
#include <Common/CurrentMetrics.h>
#include <Common/ProfileEvents.h>
namespace ProfileEvents
{
extern const Event RWLockAcquiredReadLocks;
extern const Event RWLockAcquiredWriteLocks;
extern const Event RWLockReadersWaitMilliseconds;
extern const Event RWLockWritersWaitMilliseconds;
}
namespace CurrentMetrics
{
extern const Metric RWLockWaitingReaders;
extern const Metric RWLockWaitingWriters;
extern const Metric RWLockActiveReaders;
extern const Metric RWLockActiveWriters;
}
namespace DB
{
namespace ErrorCodes
{
extern const int LOGICAL_ERROR;
}
class RWLockImpl::LockHolderImpl
{
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RWLock parent;
GroupsContainer::iterator it_group;
ClientsContainer::iterator it_client;
ThreadToHolder::key_type thread_id;
QueryIdToHolder::key_type query_id;
CurrentMetrics::Increment active_client_increment;
LockHolderImpl(RWLock && parent, GroupsContainer::iterator it_group, ClientsContainer::iterator it_client);
public:
LockHolderImpl(const LockHolderImpl & other) = delete;
~LockHolderImpl();
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friend class RWLockImpl;
};
RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String & query_id)
{
Stopwatch watch(CLOCK_MONOTONIC_COARSE);
CurrentMetrics::Increment waiting_client_increment((type == Read) ? CurrentMetrics::RWLockWaitingReaders
: CurrentMetrics::RWLockWaitingWriters);
auto finalize_metrics = [type, &watch] ()
{
ProfileEvents::increment((type == Read) ? ProfileEvents::RWLockAcquiredReadLocks
: ProfileEvents::RWLockAcquiredWriteLocks);
ProfileEvents::increment((type == Read) ? ProfileEvents::RWLockReadersWaitMilliseconds
: ProfileEvents::RWLockWritersWaitMilliseconds, watch.elapsedMilliseconds());
};
GroupsContainer::iterator it_group;
ClientsContainer::iterator it_client;
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std::unique_lock lock(mutex);
/// Check if the same query is acquiring previously acquired lock
LockHolder existing_holder_ptr;
auto this_thread_id = std::this_thread::get_id();
auto it_thread = thread_to_holder.find(this_thread_id);
auto it_query = query_id_to_holder.end();
if (query_id != RWLockImpl::NO_QUERY)
it_query = query_id_to_holder.find(query_id);
if (it_thread != thread_to_holder.end())
existing_holder_ptr = it_thread->second.lock();
else if (it_query != query_id_to_holder.end())
existing_holder_ptr = it_query->second.lock();
if (existing_holder_ptr)
{
/// XXX: it means we can't upgrade lock from read to write - with proper waiting!
if (type != Read || existing_holder_ptr->it_group->type != Read)
throw Exception("Attempt to acquire exclusive lock recursively", ErrorCodes::LOGICAL_ERROR);
return existing_holder_ptr;
}
if (type == Type::Write || queue.empty() || queue.back().type == Type::Write)
{
/// Create new group of clients
it_group = queue.emplace(queue.end(), type);
}
else
{
/// Will append myself to last group
it_group = std::prev(queue.end());
}
/// Append myself to the end of chosen group
auto & clients = it_group->clients;
try
{
it_client = clients.emplace(clients.end(), type);
}
catch (...)
{
/// Remove group if it was the first client in the group and an error occurred
if (clients.empty())
queue.erase(it_group);
throw;
}
LockHolder res(new LockHolderImpl(shared_from_this(), it_group, it_client));
/// Insert myself (weak_ptr to the holder) to threads set to implement recursive lock
thread_to_holder.emplace(this_thread_id, res);
res->thread_id = this_thread_id;
if (query_id != RWLockImpl::NO_QUERY)
query_id_to_holder.emplace(query_id, res);
res->query_id = query_id;
/// We are first, we should not wait anything
/// If we are not the first client in the group, a notification could be already sent
if (it_group == queue.begin())
{
finalize_metrics();
return res;
}
/// Wait a notification
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it_group->cv.wait(lock, [&] () { return it_group == queue.begin(); });
finalize_metrics();
return res;
}
RWLockImpl::LockHolderImpl::~LockHolderImpl()
{
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std::unique_lock lock(parent->mutex);
/// Remove weak_ptrs to the holder, since there are no owners of the current lock
parent->thread_to_holder.erase(thread_id);
parent->query_id_to_holder.erase(query_id);
/// Removes myself from client list of our group
it_group->clients.erase(it_client);
/// Remove the group if we were the last client and notify the next group
if (it_group->clients.empty())
{
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auto & parent_queue = parent->queue;
parent_queue.erase(it_group);
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if (!parent_queue.empty())
parent_queue.front().cv.notify_all();
}
}
RWLockImpl::LockHolderImpl::LockHolderImpl(RWLock && parent, RWLockImpl::GroupsContainer::iterator it_group,
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RWLockImpl::ClientsContainer::iterator it_client)
: parent{std::move(parent)}, it_group{it_group}, it_client{it_client},
active_client_increment{(*it_client == RWLockImpl::Read) ? CurrentMetrics::RWLockActiveReaders
: CurrentMetrics::RWLockActiveWriters}
{}
}