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//===--- VoucherSupport.h - Support code for OS vouchers -----------*- C++ -*-//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Support code for interfacing with OS voucher calls.
//
//===----------------------------------------------------------------------===//
#ifndef SWIFT_CONCURRENCY_VOUCHERSUPPORT_H
#define SWIFT_CONCURRENCY_VOUCHERSUPPORT_H
#include "Concurrency/Task.h"
#include "Concurrency/VoucherShims.h"
#include "TaskPrivate.h"
#include <optional>
namespace swift {
/// A class which manages voucher adoption for Job and Task objects.
class VoucherManager {
/// The original voucher that was set on the thread before Swift started
/// doing async work. This must be restored on the thread after we finish
/// async work.
std::optional<voucher_t> OriginalVoucher;
/// Determine whether vouchers are disabled entirely. This evaluates
/// true on platforms whose concurrency library does not support the
/// propagation of vouchers, in which case all of the operations of
/// this class must be no-ops.
static bool vouchersAreDisabled();
public:
VoucherManager() {
SWIFT_TASK_DEBUG_LOG("[%p] Constructing VoucherManager", this);
}
/// Clean up after completing async work, restoring the original voucher on
/// the current thread if necessary. This MUST be called before the
/// VoucherManager object is destroyed. It may also be called in other
/// places to restore the original voucher and reset the VoucherManager.
void leave() {
if (vouchersAreDisabled())
return;
if (OriginalVoucher) {
SWIFT_TASK_DEBUG_LOG("[%p] Restoring original voucher %p", this,
*OriginalVoucher);
if (swift_voucher_needs_adopt(*OriginalVoucher)) {
auto previous = voucher_adopt(*OriginalVoucher);
swift_voucher_release(previous);
} else {
swift_voucher_release(*OriginalVoucher);
}
OriginalVoucher = std::nullopt;
} else
SWIFT_TASK_DEBUG_LOG("[%p] Leaving empty VoucherManager", this);
}
~VoucherManager() { assert(!OriginalVoucher); }
/// Set up for a new Job by adopting its voucher on the current thread. This
/// takes over ownership of the voucher from the Job object. For plain Jobs,
/// this is permanent. For Tasks, the voucher must be restored using
/// restoreVoucher if the task suspends.
void swapToJob(Job *job) {
if (vouchersAreDisabled())
return;
SWIFT_TASK_DEBUG_LOG("[%p] Swapping jobs to %p", this, job);
assert(job);
assert(job->Voucher != SWIFT_DEAD_VOUCHER);
voucher_t previous;
if (swift_voucher_needs_adopt(job->Voucher)) {
// If we need to adopt the voucher, do so, and grab the old one.
SWIFT_TASK_DEBUG_LOG("[%p] Swapping jobs to %p, adopting voucher %p",
this, job, job->Voucher);
previous = voucher_adopt(job->Voucher);
} else {
// If we don't need to adopt the voucher, take the voucher out of Job
// directly.
SWIFT_TASK_DEBUG_LOG(
"[%p] Swapping jobs to to %p, voucher %p does not need adoption",
this, job, job->Voucher);
previous = job->Voucher;
}
// Either way, we've taken ownership of the job's voucher, so mark the job
// as having a dead voucher.
job->Voucher = SWIFT_DEAD_VOUCHER;
if (!OriginalVoucher) {
// If we don't yet have an original voucher, then save the one we grabbed
// above to restore later.
OriginalVoucher = previous;
SWIFT_TASK_DEBUG_LOG("[%p] Saved original voucher %p", this, previous);
} else {
// We already have an original voucher. The one we grabbed above is not
// needed. We own it, so destroy it here.
swift_voucher_release(previous);
}
}
// Take the current thread's adopted voucher and place it back into the task
// that previously owned it, re-adopting the thread's original voucher.
void restoreVoucher(AsyncTask *task) {
if (vouchersAreDisabled())
return;
SWIFT_TASK_DEBUG_LOG("[%p] Restoring %svoucher on task %p", this,
OriginalVoucher ? "" : "missing ", task);
assert(OriginalVoucher);
assert(task->Voucher == SWIFT_DEAD_VOUCHER);
if (swift_voucher_needs_adopt(*OriginalVoucher)) {
// Adopt the execution thread's original voucher. The task's voucher is
// the one currently adopted, and is returned by voucher_adopt.
task->Voucher = voucher_adopt(*OriginalVoucher);
} else {
// No need to adopt the voucher, so we can take the one out of
// OriginalVoucher and return it to the task.
task->Voucher = *OriginalVoucher;
}
// We've given up ownership of OriginalVoucher, clear it out.
OriginalVoucher = std::nullopt;
}
};
} // end namespace swift
#endif
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