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Squashed 'src/ipc/libmultiprocess/' changes from 13424cf2ecc1..47d79db8a552

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47d79db8a552 Merge bitcoin-core/libmultiprocess#201: bug: fix mptest hang, ProxyClient<Thread> deadlock in disconnect handler
f15ae9c9b9fb Merge bitcoin-core/libmultiprocess#211: Add .gitignore
4a269b21b8c8 bug: fix ProxyClient<Thread> deadlock if disconnected as IPC call is returning
85df96482c49 Use try_emplace in SetThread instead of threads.find
ca9b380ea91a Use std::optional in ConnThreads to allow shortening locks
9b0799113557 doc: describe ThreadContext struct and synchronization requirements
d60db601ed9b proxy-io.h: add Waiter::m_mutex thread safety annotations
4e365b019a9f ci: Use -Wthread-safety not -Wthread-safety-analysis
15d7bafbb001 Add .gitignore
fe1cd8c76131 Merge bitcoin-core/libmultiprocess#208: ci: Test minimum cmake version in olddeps job
b713a0b7bfbc Merge bitcoin-core/libmultiprocess#207: ci: output CMake version in CI script
0f580397c913 ci: Test minimum cmake version in olddeps job
d603dcc0eef0 ci: output CMake version in CI script

git-subtree-dir: src/ipc/libmultiprocess
git-subtree-split: 47d79db8a5528097b408e18f7b0bae11a6702d26
This commit is contained in:
Ryan Ofsky
2025-09-17 05:30:43 -04:00
parent a334bbe9b7
commit 535fa0ad0d
11 changed files with 189 additions and 78 deletions
Download Patch File Download Diff File Expand all files Collapse all files

72
include/mp/proxy-io.h
View File

@@ -66,8 +66,6 @@ struct ProxyClient<Thread> : public ProxyClientBase<Thread, ::capnp::Void>
ProxyClient(const ProxyClient&) = delete;
~ProxyClient();
void setDisconnectCallback(const std::function<void()>& fn);
//! Reference to callback function that is run if there is a sudden
//! disconnect and the Connection object is destroyed before this
//! ProxyClient<Thread> object. The callback will destroy this object and
@@ -285,16 +283,16 @@ struct Waiter
template <typename Fn>
void post(Fn&& fn)
{
const std::unique_lock<std::mutex> lock(m_mutex);
const Lock lock(m_mutex);
assert(!m_fn);
m_fn = std::forward<Fn>(fn);
m_cv.notify_all();
}
template <class Predicate>
void wait(std::unique_lock<std::mutex>& lock, Predicate pred)
void wait(Lock& lock, Predicate pred)
{
m_cv.wait(lock, [&] {
m_cv.wait(lock.m_lock, [&]() MP_REQUIRES(m_mutex) {
// Important for this to be "while (m_fn)", not "if (m_fn)" to avoid
// a lost-wakeup bug. A new m_fn and m_cv notification might be sent
// after the fn() call and before the lock.lock() call in this loop
@@ -317,9 +315,9 @@ struct Waiter
//! mutexes than necessary. This mutex can be held at the same time as
//! EventLoop::m_mutex as long as Waiter::mutex is locked first and
//! EventLoop::m_mutex is locked second.
std::mutex m_mutex;
Mutex m_mutex;
std::condition_variable m_cv;
std::optional<kj::Function<void()>> m_fn;
std::optional<kj::Function<void()>> m_fn MP_GUARDED_BY(m_mutex);
};
//! Object holding network & rpc state associated with either an incoming server
@@ -544,29 +542,73 @@ void ProxyServerBase<Interface, Impl>::invokeDestroy()
CleanupRun(m_context.cleanup_fns);
}
using ConnThreads = std::map<Connection*, ProxyClient<Thread>>;
//! Map from Connection to local or remote thread handle which will be used over
//! that connection. This map will typically only contain one entry, but can
//! contain multiple if a single thread makes IPC calls over multiple
//! connections. A std::optional value type is used to avoid the map needing to
//! be locked while ProxyClient<Thread> objects are constructed, see
//! ThreadContext "Synchronization note" below.
using ConnThreads = std::map<Connection*, std::optional<ProxyClient<Thread>>>;
using ConnThread = ConnThreads::iterator;
// Retrieve ProxyClient<Thread> object associated with this connection from a
// map, or create a new one and insert it into the map. Return map iterator and
// inserted bool.
std::tuple<ConnThread, bool> SetThread(ConnThreads& threads, std::mutex& mutex, Connection* connection, const std::function<Thread::Client()>& make_thread);
std::tuple<ConnThread, bool> SetThread(GuardedRef<ConnThreads> threads, Connection* connection, const std::function<Thread::Client()>& make_thread);
//! The thread_local ThreadContext g_thread_context struct provides information
//! about individual threads and a way of communicating between them. Because
//! it's a thread local struct, each ThreadContext instance is initialized by
//! the thread that owns it.
//!
//! ThreadContext is used for any client threads created externally which make
//! IPC calls, and for server threads created by
//! ProxyServer<ThreadMap>::makeThread() which execute IPC calls for clients.
//!
//! In both cases, the struct holds information like the thread name, and a
//! Waiter object where the EventLoop can post incoming IPC requests to execute
//! on the thread. The struct also holds ConnThread maps associating the thread
//! with local and remote ProxyClient<Thread> objects.
struct ThreadContext
{
//! Identifying string for debug.
std::string thread_name;
//! Waiter object used to allow client threads blocked waiting for a server
//! response to execute callbacks made from the client's corresponding
//! server thread.
//! Waiter object used to allow remote clients to execute code on this
//! thread. For server threads created by
//! ProxyServer<ThreadMap>::makeThread(), this is initialized in that
//! function. Otherwise, for client threads created externally, this is
//! initialized the first time the thread tries to make an IPC call. Having
//! a waiter is necessary for threads making IPC calls in case a server they
//! are calling expects them to execute a callback during the call, before
//! it sends a response.
//!
//! For IPC client threads, the Waiter pointer is never cleared and the Waiter
//! just gets destroyed when the thread does. For server threads created by
//! makeThread(), this pointer is set to null in the ~ProxyServer<Thread> as
//! a signal for the thread to exit and destroy itself. In both cases, the
//! same Waiter object is used across different calls and only created and
//! destroyed once for the lifetime of the thread.
std::unique_ptr<Waiter> waiter = nullptr;
//! When client is making a request to a server, this is the
//! `callbackThread` argument it passes in the request, used by the server
//! in case it needs to make callbacks into the client that need to execute
//! while the client is waiting. This will be set to a local thread object.
ConnThreads callback_threads;
//!
//! Synchronization note: The callback_thread and request_thread maps are
//! only ever accessed internally by this thread's destructor and externally
//! by Cap'n Proto event loop threads. Since it's possible for IPC client
//! threads to make calls over different connections that could have
//! different event loops, these maps are guarded by Waiter::m_mutex in case
//! different event loop threads add or remove map entries simultaneously.
//! However, individual ProxyClient<Thread> objects in the maps will only be
//! associated with one event loop and guarded by EventLoop::m_mutex. So
//! Waiter::m_mutex does not need to be held while accessing individual
//! ProxyClient<Thread> instances, and may even need to be released to
//! respect lock order and avoid locking Waiter::m_mutex before
//! EventLoop::m_mutex.
ConnThreads callback_threads MP_GUARDED_BY(waiter->m_mutex);
//! When client is making a request to a server, this is the `thread`
//! argument it passes in the request, used to control which thread on
@@ -575,7 +617,9 @@ struct ThreadContext
//! by makeThread. If a client call is being made from a thread currently
//! handling a server request, this will be set to the `callbackThread`
//! request thread argument passed in that request.
ConnThreads request_threads;
//!
//! Synchronization note: \ref callback_threads note applies here as well.
ConnThreads request_threads MP_GUARDED_BY(waiter->m_mutex);
//! Whether this thread is a capnp event loop thread. Not really used except
//! to assert false if there's an attempt to execute a blocking operation

8
include/mp/proxy-types.h
View File

@@ -617,7 +617,7 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
const char* disconnected = nullptr;
proxy_client.m_context.loop->sync([&]() {
if (!proxy_client.m_context.connection) {
const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
const Lock lock(thread_context.waiter->m_mutex);
done = true;
disconnected = "IPC client method called after disconnect.";
thread_context.waiter->m_cv.notify_all();
@@ -644,7 +644,7 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
} catch (...) {
exception = std::current_exception();
}
const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
const Lock lock(thread_context.waiter->m_mutex);
done = true;
thread_context.waiter->m_cv.notify_all();
},
@@ -656,13 +656,13 @@ void clientInvoke(ProxyClient& proxy_client, const GetRequest& get_request, Fiel
proxy_client.m_context.loop->logPlain()
<< "{" << thread_context.thread_name << "} IPC client exception " << kj_exception;
}
const std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
const Lock lock(thread_context.waiter->m_mutex);
done = true;
thread_context.waiter->m_cv.notify_all();
}));
});
std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
Lock lock(thread_context.waiter->m_mutex);
thread_context.waiter->wait(lock, [&done]() { return done; });
if (exception) std::rethrow_exception(exception);
if (!kj_exception.empty()) proxy_client.m_context.loop->raise() << kj_exception;

50
include/mp/type-context.h
View File

@@ -25,7 +25,7 @@ void CustomBuildField(TypeList<>,
// Also store the Thread::Client reference in the callback_threads map so
// future calls over this connection can reuse it.
auto [callback_thread, _]{SetThread(
thread_context.callback_threads, thread_context.waiter->m_mutex, &connection,
GuardedRef{thread_context.waiter->m_mutex, thread_context.callback_threads}, &connection,
[&] { return connection.m_threads.add(kj::heap<ProxyServer<Thread>>(thread_context, std::thread{})); })};
// Call remote ThreadMap.makeThread function so server will create a
@@ -43,12 +43,12 @@ void CustomBuildField(TypeList<>,
return request.send().getResult(); // Nonblocking due to capnp request pipelining.
}};
auto [request_thread, _1]{SetThread(
thread_context.request_threads, thread_context.waiter->m_mutex,
GuardedRef{thread_context.waiter->m_mutex, thread_context.request_threads},
&connection, make_request_thread)};
auto context = output.init();
context.setThread(request_thread->second.m_client);
context.setCallbackThread(callback_thread->second.m_client);
context.setThread(request_thread->second->m_client);
context.setCallbackThread(callback_thread->second->m_client);
}
//! PassField override for mp.Context arguments. Return asynchronously and call
@@ -89,29 +89,39 @@ auto PassField(Priority<1>, TypeList<>, ServerContext& server_context, const Fn&
// need to update the map.
auto& thread_context = g_thread_context;
auto& request_threads = thread_context.request_threads;
auto [request_thread, inserted]{SetThread(
request_threads, thread_context.waiter->m_mutex,
server.m_context.connection,
[&] { return context_arg.getCallbackThread(); })};
ConnThread request_thread;
bool inserted;
server.m_context.loop->sync([&] {
std::tie(request_thread, inserted) = SetThread(
GuardedRef{thread_context.waiter->m_mutex, request_threads}, server.m_context.connection,
[&] { return context_arg.getCallbackThread(); });
});
// If an entry was inserted into the requests_threads map,
// If an entry was inserted into the request_threads map,
// remove it after calling fn.invoke. If an entry was not
// inserted, one already existed, meaning this must be a
// recursive call (IPC call calling back to the caller which
// makes another IPC call), so avoid modifying the map.
const bool erase_thread{inserted};
KJ_DEFER(if (erase_thread) {
std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex);
// Call erase here with a Connection* argument instead
// of an iterator argument, because the `request_thread`
// iterator may be invalid if the connection is closed
// during this function call. More specifically, the
// iterator may be invalid because SetThread adds a
// cleanup callback to the Connection destructor that
// erases the thread from the map, and also because the
// ProxyServer<Thread> destructor calls
// request_threads.clear().
request_threads.erase(server.m_context.connection);
// Erase the request_threads entry on the event loop
// thread with loop->sync(), so if the connection is
// broken there is not a race between this thread and
// the disconnect handler trying to destroy the thread
// client object.
server.m_context.loop->sync([&] {
// Look up the thread again without using existing
// iterator since entry may no longer be there after
// a disconnect. Destroy node after releasing
// Waiter::m_mutex, so the ProxyClient<Thread>
// destructor is able to use EventLoop::mutex
// without violating lock order.
ConnThreads::node_type removed;
{
Lock lock(thread_context.waiter->m_mutex);
removed = request_threads.extract(server.m_context.connection);
}
});
});
fn.invoke(server_context, args...);
}

11
include/mp/util.h
View File

@@ -182,6 +182,17 @@ public:
std::unique_lock<std::mutex> m_lock;
};
template<typename T>
struct GuardedRef
{
Mutex& mutex;
T& ref MP_GUARDED_BY(mutex);
};
// CTAD for Clang 16: GuardedRef{mutex, x} -> GuardedRef<decltype(x)>
template <class U>
GuardedRef(Mutex&, U&) -> GuardedRef<U>;
//! Analog to std::lock_guard that unlocks instead of locks.
template <typename Lock>
struct UnlockGuard