ClickHouse/dbms/src/Storages/System/StorageSystemStackTrace.cpp

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#ifdef OS_LINUX /// Because of 'sigqueue' functions and RT signals.
#include <signal.h>
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#include <poll.h>
#include <mutex>
#include <filesystem>
#include <ext/scope_guard.h>
#include <Storages/System/StorageSystemStackTrace.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/DataTypeArray.h>
#include <IO/ReadHelpers.h>
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#include <Common/PipeFDs.h>
#include <common/getThreadNumber.h>
namespace DB
{
namespace ErrorCodes
{
extern const int CANNOT_SIGQUEUE;
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extern const int CANNOT_MANIPULATE_SIGSET;
extern const int CANNOT_SET_SIGNAL_HANDLER;
extern const int CANNOT_READ_FROM_FILE_DESCRIPTOR;
extern const int LOGICAL_ERROR;
}
namespace
{
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const pid_t expected_pid = getpid();
const int sig = SIGRTMIN;
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int sequence_num = 0; /// For messages sent via pipe.
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UInt32 thread_number{0};
std::optional<StackTrace> stack_trace;
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static constexpr size_t max_query_id_size = 128;
char query_id_data[max_query_id_size];
size_t query_id_size = 0;
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LazyPipeFDs notification_pipe;
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void signalHandler(int, siginfo_t * info, void * context)
{
/// In case malicious user is sending signals manually (for unknown reason).
/// If we don't check - it may break our synchronization.
if (info->si_pid != expected_pid)
return;
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/// Signal received too late.
if (info->si_value.sival_int != sequence_num)
return;
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/// All these methods are signal-safe.
const ucontext_t signal_context = *reinterpret_cast<ucontext_t *>(context);
stack_trace.emplace(signal_context);
thread_number = getThreadNumber();
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StringRef query_id = CurrentThread::getQueryId();
query_id_size = std::min(query_id.size, max_query_id_size);
memcpy(query_id_data, query_id.data, query_id_size);
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int notification_num = info->si_value.sival_int;
ssize_t res = ::write(notification_pipe.fds_rw[1], &notification_num, sizeof(notification_num));
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/// We cannot do anything if write failed.
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(void)res;
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}
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/// Wait for data in pipe and read it.
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bool wait(int timeout_ms)
{
while (true)
{
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int fd = notification_pipe.fds_rw[0];
pollfd poll_fd{fd, POLLIN, 0};
int poll_res = poll(&poll_fd, 1, timeout_ms);
if (poll_res < 0)
{
if (errno == EINTR)
{
--timeout_ms; /// Quite a hacky way to update timeout. Just to make sure we avoid infinite waiting.
if (timeout_ms == 0)
return false;
continue;
}
throwFromErrno("Cannot poll pipe", ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
}
if (poll_res == 0)
return false;
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int notification_num = 0;
ssize_t read_res = ::read(fd, &notification_num, sizeof(notification_num));
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if (read_res < 0)
{
if (errno == EINTR)
continue;
throwFromErrno("Cannot read from pipe", ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
}
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if (read_res == sizeof(notification_num))
{
if (notification_num == sequence_num)
return true;
else
continue; /// Drain delayed notifications.
}
throw Exception("Logical error: read wrong number of bytes from pipe", ErrorCodes::LOGICAL_ERROR);
}
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}
}
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StorageSystemStackTrace::StorageSystemStackTrace(const String & name_)
: IStorageSystemOneBlock<StorageSystemStackTrace>(name_)
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{
notification_pipe.open();
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/// Setup signal handler.
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struct sigaction sa{};
sa.sa_sigaction = signalHandler;
sa.sa_flags = SA_SIGINFO;
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if (sigemptyset(&sa.sa_mask))
throwFromErrno("Cannot set signal handler.", ErrorCodes::CANNOT_MANIPULATE_SIGSET);
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if (sigaddset(&sa.sa_mask, sig))
throwFromErrno("Cannot set signal handler.", ErrorCodes::CANNOT_MANIPULATE_SIGSET);
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if (sigaction(sig, &sa, nullptr))
throwFromErrno("Cannot set signal handler.", ErrorCodes::CANNOT_SET_SIGNAL_HANDLER);
}
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NamesAndTypesList StorageSystemStackTrace::getNamesAndTypes()
{
return
{
{ "thread_number", std::make_shared<DataTypeUInt32>() },
{ "query_id", std::make_shared<DataTypeString>() },
{ "trace", std::make_shared<DataTypeArray>(std::make_shared<DataTypeUInt64>()) }
};
}
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void StorageSystemStackTrace::fillData(MutableColumns & res_columns, const Context &, const SelectQueryInfo &) const
{
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/// It shouldn't be possible to do concurrent reads from this table.
std::lock_guard lock(mutex);
/// Send a signal to every thread and wait for result.
/// We must wait for every thread one by one sequentially,
/// because there is a limit on number of queued signals in OS and otherwise signals may get lost.
/// Also, non-RT signals are not delivered if previous signal is handled right now (by default; but we use RT signals).
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/// Obviously, results for different threads may be out of sync.
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/// There is no better way to enumerate threads in a process other than looking into procfs.
std::filesystem::directory_iterator end;
for (std::filesystem::directory_iterator it("/proc/self/task"); it != end; ++it)
{
pid_t tid = parse<pid_t>(it->path().filename());
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sigval sig_value{};
sig_value.sival_int = sequence_num;
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if (0 != ::sigqueue(tid, sig, sig_value))
{
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/// The thread may has been already finished.
if (ESRCH == errno)
continue;
throwFromErrno("Cannot send signal with sigqueue", ErrorCodes::CANNOT_SIGQUEUE);
}
/// Just in case we will wait for pipe with timeout. In case signal didn't get processed.
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if (wait(100))
{
size_t stack_trace_size = stack_trace->getSize();
size_t stack_trace_offset = stack_trace->getOffset();
Array arr;
arr.reserve(stack_trace_size - stack_trace_offset);
for (size_t i = stack_trace_offset; i < stack_trace_size; ++i)
arr.emplace_back(reinterpret_cast<intptr_t>(stack_trace->getFrames()[i]));
res_columns[0]->insert(thread_number);
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res_columns[1]->insertData(query_id_data, query_id_size);
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res_columns[2]->insert(arr);
}
else
{
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/// Cannot obtain a stack trace. But create a record in result nevertheless.
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res_columns[0]->insert(tid); /// TODO Replace all thread numbers to OS thread numbers.
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res_columns[1]->insertDefault();
res_columns[2]->insertDefault();
}
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sequence_num = static_cast<int>(static_cast<unsigned>(sequence_num) + 1);
}
}
}
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#endif