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/*
*
* Copyright 2017 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#ifndef GRPC_CORE_LIB_IOMGR_CALL_COMBINER_H
#define GRPC_CORE_LIB_IOMGR_CALL_COMBINER_H
#include <grpc/support/port_platform.h>
#include <stddef.h>
#include <grpc/support/atm.h>
#include "src/core/lib/gpr/mpscq.h"
#include "src/core/lib/gprpp/inlined_vector.h"
#include "src/core/lib/iomgr/closure.h"
// A simple, lock-free mechanism for serializing activity related to a
// single call. This is similar to a combiner but is more lightweight.
//
// It requires the callback (or, in the common case where the callback
// actually kicks off a chain of callbacks, the last callback in that
// chain) to explicitly indicate (by calling GRPC_CALL_COMBINER_STOP())
// when it is done with the action that was kicked off by the original
// callback.
extern grpc_core::TraceFlag grpc_call_combiner_trace;
typedef struct {
gpr_atm size = 0; // size_t, num closures in queue or currently executing
gpr_mpscq queue;
// Either 0 (if not cancelled and no cancellation closure set),
// a grpc_closure* (if the lowest bit is 0),
// or a grpc_error* (if the lowest bit is 1).
gpr_atm cancel_state = 0;
} grpc_call_combiner;
// Assumes memory was initialized to zero.
void grpc_call_combiner_init(grpc_call_combiner* call_combiner);
void grpc_call_combiner_destroy(grpc_call_combiner* call_combiner);
#ifndef NDEBUG
#define GRPC_CALL_COMBINER_START(call_combiner, closure, error, reason) \
grpc_call_combiner_start((call_combiner), (closure), (error), __FILE__, \
__LINE__, (reason))
#define GRPC_CALL_COMBINER_STOP(call_combiner, reason) \
grpc_call_combiner_stop((call_combiner), __FILE__, __LINE__, (reason))
/// Starts processing \a closure on \a call_combiner.
void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
grpc_closure* closure, grpc_error* error,
const char* file, int line, const char* reason);
/// Yields the call combiner to the next closure in the queue, if any.
void grpc_call_combiner_stop(grpc_call_combiner* call_combiner,
const char* file, int line, const char* reason);
#else
#define GRPC_CALL_COMBINER_START(call_combiner, closure, error, reason) \
grpc_call_combiner_start((call_combiner), (closure), (error), (reason))
#define GRPC_CALL_COMBINER_STOP(call_combiner, reason) \
grpc_call_combiner_stop((call_combiner), (reason))
/// Starts processing \a closure on \a call_combiner.
void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
grpc_closure* closure, grpc_error* error,
const char* reason);
/// Yields the call combiner to the next closure in the queue, if any.
void grpc_call_combiner_stop(grpc_call_combiner* call_combiner,
const char* reason);
#endif
/// Registers \a closure to be invoked by \a call_combiner when
/// grpc_call_combiner_cancel() is called.
///
/// Once a closure is registered, it will always be scheduled exactly
/// once; this allows the closure to hold references that will be freed
/// regardless of whether or not the call was cancelled. If a cancellation
/// does occur, the closure will be scheduled with the cancellation error;
/// otherwise, it will be scheduled with GRPC_ERROR_NONE.
///
/// The closure will be scheduled in the following cases:
/// - If grpc_call_combiner_cancel() was called prior to registering the
/// closure, it will be scheduled immediately with the cancelation error.
/// - If grpc_call_combiner_cancel() is called after registering the
/// closure, the closure will be scheduled with the cancellation error.
/// - If grpc_call_combiner_set_notify_on_cancel() is called again to
/// register a new cancellation closure, the previous cancellation
/// closure will be scheduled with GRPC_ERROR_NONE.
///
/// If \a closure is NULL, then no closure will be invoked on
/// cancellation; this effectively unregisters the previously set closure.
/// However, most filters will not need to explicitly unregister their
/// callbacks, as this is done automatically when the call is destroyed. Filters
/// that schedule the cancellation closure on ExecCtx do not need to take a ref
/// on the call stack to guarantee closure liveness. This is done by explicitly
/// flushing ExecCtx after the unregistration during call destruction.
void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
grpc_closure* closure);
/// Indicates that the call has been cancelled.
void grpc_call_combiner_cancel(grpc_call_combiner* call_combiner,
grpc_error* error);
namespace grpc_core {
// Helper for running a list of closures in a call combiner.
//
// Each callback running in the call combiner will eventually be
// returned to the surface, at which point the surface will yield the
// call combiner. So when we are running in the call combiner and have
// more than one callback to return to the surface, we need to re-enter
// the call combiner for all but one of those callbacks.
class CallCombinerClosureList {
public:
CallCombinerClosureList() {}
// Adds a closure to the list. The closure must eventually result in
// the call combiner being yielded.
void Add(grpc_closure* closure, grpc_error* error, const char* reason) {
closures_.emplace_back(closure, error, reason);
}
// Runs all closures in the call combiner and yields the call combiner.
//
// All but one of the closures in the list will be scheduled via
// GRPC_CALL_COMBINER_START(), and the remaining closure will be
// scheduled via GRPC_CLOSURE_SCHED(), which will eventually result in
// yielding the call combiner. If the list is empty, then the call
// combiner will be yielded immediately.
void RunClosures(grpc_call_combiner* call_combiner) {
if (closures_.empty()) {
GRPC_CALL_COMBINER_STOP(call_combiner, "no closures to schedule");
return;
}
for (size_t i = 1; i < closures_.size(); ++i) {
auto& closure = closures_[i];
GRPC_CALL_COMBINER_START(call_combiner, closure.closure, closure.error,
closure.reason);
}
if (grpc_call_combiner_trace.enabled()) {
gpr_log(GPR_INFO,
"CallCombinerClosureList executing closure while already "
"holding call_combiner %p: closure=%p error=%s reason=%s",
call_combiner, closures_[0].closure,
grpc_error_string(closures_[0].error), closures_[0].reason);
}
// This will release the call combiner.
GRPC_CLOSURE_SCHED(closures_[0].closure, closures_[0].error);
closures_.clear();
}
// Runs all closures in the call combiner, but does NOT yield the call
// combiner. All closures will be scheduled via GRPC_CALL_COMBINER_START().
void RunClosuresWithoutYielding(grpc_call_combiner* call_combiner) {
for (size_t i = 0; i < closures_.size(); ++i) {
auto& closure = closures_[i];
GRPC_CALL_COMBINER_START(call_combiner, closure.closure, closure.error,
closure.reason);
}
closures_.clear();
}
size_t size() const { return closures_.size(); }
private:
struct CallCombinerClosure {
grpc_closure* closure;
grpc_error* error;
const char* reason;
CallCombinerClosure(grpc_closure* closure, grpc_error* error,
const char* reason)
: closure(closure), error(error), reason(reason) {}
};
// There are generally a maximum of 6 closures to run in the call
// combiner, one for each pending op.
InlinedVector<CallCombinerClosure, 6> closures_;
};
} // namespace grpc_core
#endif /* GRPC_CORE_LIB_IOMGR_CALL_COMBINER_H */