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Better handling of signals

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This commit is contained in:
Alexey Milovidov 2019-12-23 22:23:54 +03:00
parent e907ce103e
commit 3b7f3b07cd
2 changed files with 24 additions and 9 deletions
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32
dbms/src/Storages/System/StorageSystemStackTrace.cpp
View File

@ -35,6 +35,8 @@ namespace
const pid_t expected_pid = getpid();
const int sig = SIGRTMIN;
int sequence_num = 0; /// For messages sent via pipe.
UInt32 thread_number{0};
std::optional<StackTrace> stack_trace;
@ -51,6 +53,10 @@ namespace
if (info->si_pid != expected_pid)
return;
/// Signal received too late.
if (info->si_value.sival_int != sequence_num)
return;
/// All these methods are signal-safe.
const ucontext_t signal_context = *reinterpret_cast<ucontext_t *>(context);
stack_trace.emplace(signal_context);
@ -60,8 +66,8 @@ namespace
query_id_size = std::min(query_id.size, max_query_id_size);
memcpy(query_id_data, query_id.data, query_id_size);
char buf = 0;
ssize_t res = ::write(notification_pipe.fds_rw[1], &buf, 1);
int notification_num = info->si_value.sival_int;
ssize_t res = ::write(notification_pipe.fds_rw[1], &notification_num, sizeof(notification_num));
/// We cannot do anything if write failed.
(void)res;
@ -91,10 +97,8 @@ namespace
if (poll_res == 0)
return false;
char buf = 0;
ssize_t read_res = ::read(fd, &buf, 1);
if (read_res == 1)
return true;
int notification_num = 0;
ssize_t read_res = ::read(fd, &notification_num, sizeof(notification_num));
if (read_res < 0)
{
@ -104,7 +108,15 @@ namespace
throwFromErrno("Cannot read from pipe", ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
}
throw Exception("Logical error: read for one byte returned more than one byte", ErrorCodes::LOGICAL_ERROR);
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);
}
}
}
@ -160,9 +172,10 @@ void StorageSystemStackTrace::fillData(MutableColumns & res_columns, const Conte
std::filesystem::directory_iterator end;
for (std::filesystem::directory_iterator it("/proc/self/task"); it != end; ++it)
{
sigval sig_value{};
pid_t tid = parse<pid_t>(it->path().filename());
sigval sig_value{};
sig_value.sival_int = sequence_num;
if (0 != ::sigqueue(tid, sig, sig_value))
{
/// The thread may has been already finished.
@ -173,7 +186,6 @@ void StorageSystemStackTrace::fillData(MutableColumns & res_columns, const Conte
}
/// Just in case we will wait for pipe with timeout. In case signal didn't get processed.
/// TODO How to deal with stale values in a pipe? TSan will also argue.
if (wait(100))
{
@ -197,6 +209,8 @@ void StorageSystemStackTrace::fillData(MutableColumns & res_columns, const Conte
res_columns[1]->insertDefault();
res_columns[2]->insertDefault();
}
sequence_num = static_cast<int>(static_cast<unsigned>(sequence_num) + 1);
}
}

1
dbms/src/Storages/System/StorageSystemStackTrace.h
View File

@ -15,6 +15,7 @@ class Context;
/// Allows to introspect stack trace of all server threads.
/// It acts like an embedded debugger.
/// More than one instance of this table cannot be used.
class StorageSystemStackTrace : public ext::shared_ptr_helper<StorageSystemStackTrace>, public IStorageSystemOneBlock<StorageSystemStackTrace>
{
friend struct ext::shared_ptr_helper<StorageSystemStackTrace>;