104 lines
3.9 KiB
C++
104 lines
3.9 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Core interfaces and definitions used by by low-level interfaces such as
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// SpinLock.
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#ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
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#define ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
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#include "absl/base/internal/scheduling_mode.h"
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#include "absl/base/macros.h"
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// The following two declarations exist so SchedulingGuard may friend them with
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// the appropriate language linkage. These callbacks allow libc internals, such
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// as function level statics, to schedule cooperatively when locking.
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extern "C" bool __google_disable_rescheduling(void);
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extern "C" void __google_enable_rescheduling(bool disable_result);
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namespace absl {
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namespace base_internal {
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class SchedulingHelper; // To allow use of SchedulingGuard.
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class SpinLock; // To allow use of SchedulingGuard.
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// SchedulingGuard
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// Provides guard semantics that may be used to disable cooperative rescheduling
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// of the calling thread within specific program blocks. This is used to
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// protect resources (e.g. low-level SpinLocks or Domain code) that cooperative
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// scheduling depends on.
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//
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// Domain implementations capable of rescheduling in reaction to involuntary
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// kernel thread actions (e.g blocking due to a pagefault or syscall) must
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// guarantee that an annotated thread is not allowed to (cooperatively)
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// reschedule until the annotated region is complete.
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//
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// It is an error to attempt to use a cooperatively scheduled resource (e.g.
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// Mutex) within a rescheduling-disabled region.
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//
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// All methods are async-signal safe.
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class SchedulingGuard {
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public:
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// Returns true iff the calling thread may be cooperatively rescheduled.
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static bool ReschedulingIsAllowed();
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private:
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// Disable cooperative rescheduling of the calling thread. It may still
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// initiate scheduling operations (e.g. wake-ups), however, it may not itself
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// reschedule. Nestable. The returned result is opaque, clients should not
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// attempt to interpret it.
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// REQUIRES: Result must be passed to a pairing EnableScheduling().
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static bool DisableRescheduling();
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// Marks the end of a rescheduling disabled region, previously started by
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// DisableRescheduling().
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// REQUIRES: Pairs with innermost call (and result) of DisableRescheduling().
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static void EnableRescheduling(bool disable_result);
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// A scoped helper for {Disable, Enable}Rescheduling().
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// REQUIRES: destructor must run in same thread as constructor.
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struct ScopedDisable {
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ScopedDisable() { disabled = SchedulingGuard::DisableRescheduling(); }
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~ScopedDisable() { SchedulingGuard::EnableRescheduling(disabled); }
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bool disabled;
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};
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// Access to SchedulingGuard is explicitly white-listed.
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friend class SchedulingHelper;
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friend class SpinLock;
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SchedulingGuard(const SchedulingGuard&) = delete;
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SchedulingGuard& operator=(const SchedulingGuard&) = delete;
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};
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//------------------------------------------------------------------------------
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// End of public interfaces.
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//------------------------------------------------------------------------------
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inline bool SchedulingGuard::ReschedulingIsAllowed() {
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return false;
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}
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inline bool SchedulingGuard::DisableRescheduling() {
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return false;
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}
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inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) {
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return;
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}
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} // namespace base_internal
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} // namespace absl
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#endif // ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
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