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/**
* Copyright (C) 2022-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/util/concurrency/semaphore_ticketholder.h"
#include <iostream>
#include "mongo/db/service_context.h"
#include "mongo/logv2/log.h"
#include "mongo/util/concurrency/ticketholder.h"
#include "mongo/util/str.h"
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kDefault
namespace mongo {
int64_t SemaphoreTicketHolder::numFinishedProcessing() const {
return _semaphoreStats.totalFinishedProcessing.load();
}
void SemaphoreTicketHolder::_appendImplStats(BSONObjBuilder& b) const {
_appendCommonQueueImplStats(b, _semaphoreStats);
}
#if defined(__linux__)
namespace {
/**
* Accepts an errno code, prints its error message, and exits.
*/
void failWithErrno(int err) {
LOGV2_FATAL(28604,
"error in Ticketholder: {errnoWithDescription_err}",
"errnoWithDescription_err"_attr = errorMessage(posixError(err)));
}
/*
* Checks the return value from a Linux semaphore function call, and fails with the set errno if the
* call was unsucessful.
*/
void check(int ret) {
if (ret == 0)
return;
failWithErrno(errno);
}
/**
* Takes a Date_t deadline and sets the appropriate values in a timespec structure.
*/
void tsFromDate(const Date_t& deadline, struct timespec& ts) {
ts.tv_sec = deadline.toTimeT();
ts.tv_nsec = (deadline.toMillisSinceEpoch() % 1000) * 1'000'000;
}
} // namespace
SemaphoreTicketHolder::SemaphoreTicketHolder(int numTickets, ServiceContext* serviceContext)
: TicketHolder(numTickets, serviceContext) {
check(sem_init(&_sem, 0, numTickets));
}
SemaphoreTicketHolder::~SemaphoreTicketHolder() {
check(sem_destroy(&_sem));
}
boost::optional<Ticket> SemaphoreTicketHolder::_tryAcquireImpl(AdmissionContext* admCtx) {
while (0 != sem_trywait(&_sem)) {
if (errno == EAGAIN)
return boost::none;
if (errno != EINTR)
failWithErrno(errno);
}
return Ticket{this, admCtx};
}
boost::optional<Ticket> SemaphoreTicketHolder::_waitForTicketUntilImpl(OperationContext* opCtx,
AdmissionContext* admCtx,
Date_t until) {
const Milliseconds intervalMs(500);
struct timespec ts;
// To support interrupting ticket acquisition while still benefiting from semaphores, we do a
// timed wait on an interval to periodically check for interrupts.
// The wait period interval is the smaller of the default interval and the provided
// deadline.
Date_t deadline = std::min(until, Date_t::now() + intervalMs);
tsFromDate(deadline, ts);
while (0 != sem_timedwait(&_sem, &ts)) {
if (errno == ETIMEDOUT) {
// If we reached the deadline without being interrupted, we have completely timed out.
if (deadline == until)
return boost::none;
deadline = std::min(until, Date_t::now() + intervalMs);
tsFromDate(deadline, ts);
} else if (errno != EINTR) {
failWithErrno(errno);
}
// To correctly handle errors from sem_timedwait, we should check for interrupts last.
// It is possible to unset 'errno' after a call to checkForInterrupt().
if (opCtx)
opCtx->checkForInterrupt();
}
return Ticket{this, admCtx};
}
void SemaphoreTicketHolder::_releaseToTicketPoolImpl(AdmissionContext* admCtx) noexcept {
check(sem_post(&_sem));
}
int32_t SemaphoreTicketHolder::available() const {
int val = 0;
check(sem_getvalue(&_sem, &val));
return val;
}
void SemaphoreTicketHolder::_resize(int32_t newSize, int32_t oldSize) noexcept {
auto difference = newSize - oldSize;
if (difference > 0) {
for (int32_t i = 0; i < difference; i++) {
check(sem_post(&_sem));
}
} else if (difference < 0) {
for (int32_t i = 0; i < -difference; i++) {
check(sem_wait(&_sem));
}
}
}
#else
SemaphoreTicketHolder::SemaphoreTicketHolder(int32_t numTickets, ServiceContext* svcCtx)
: TicketHolder(numTickets, svcCtx), _numTickets(numTickets) {}
SemaphoreTicketHolder::~SemaphoreTicketHolder() = default;
boost::optional<Ticket> SemaphoreTicketHolder::_tryAcquireImpl(AdmissionContext* admCtx) {
stdx::lock_guard<Latch> lk(_mutex);
if (!_tryAcquire()) {
return boost::none;
}
return Ticket{this, admCtx};
}
boost::optional<Ticket> SemaphoreTicketHolder::_waitForTicketUntilImpl(OperationContext* opCtx,
AdmissionContext* admCtx,
Date_t until) {
stdx::unique_lock<Latch> lk(_mutex);
bool taken = [&] {
if (opCtx) {
return opCtx->waitForConditionOrInterruptUntil(
_newTicket, lk, until, [this] { return _tryAcquire(); });
} else {
if (until == Date_t::max()) {
_newTicket.wait(lk, [this] { return _tryAcquire(); });
return true;
} else {
return _newTicket.wait_until(
lk, until.toSystemTimePoint(), [this] { return _tryAcquire(); });
}
}
}();
if (!taken) {
return boost::none;
}
return Ticket{this, admCtx};
}
void SemaphoreTicketHolder::_releaseToTicketPoolImpl(AdmissionContext* admCtx) noexcept {
{
stdx::lock_guard<Latch> lk(_mutex);
_numTickets++;
}
_newTicket.notify_one();
}
int32_t SemaphoreTicketHolder::available() const {
return _numTickets;
}
bool SemaphoreTicketHolder::_tryAcquire() {
if (_numTickets <= 0) {
return false;
}
_numTickets--;
return true;
}
void SemaphoreTicketHolder::_resize(int32_t newSize, int32_t oldSize) noexcept {
auto difference = newSize - oldSize;
stdx::lock_guard<Latch> lk(_mutex);
_numTickets += difference;
if (difference > 0) {
for (int32_t i = 0; i < difference; i++) {
_newTicket.notify_one();
}
}
// No need to do anything in the other cases as the number of tickets being <= 0 implies they'll
// have to wait until the current ticket holders release their tickets.
}
#endif
} // namespace mongo
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