1 /*
2 *
3 * Copyright 2016 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19 #include <grpc/support/port_platform.h>
20
21 #include "src/core/lib/iomgr/combiner.h"
22
23 #include <assert.h>
24 #include <inttypes.h>
25 #include <string.h>
26
27 #include <grpc/support/alloc.h>
28 #include <grpc/support/log.h>
29
30 #include "src/core/lib/debug/stats.h"
31 #include "src/core/lib/gprpp/mpscq.h"
32 #include "src/core/lib/iomgr/executor.h"
33 #include "src/core/lib/iomgr/iomgr.h"
34 #include "src/core/lib/profiling/timers.h"
35
36 grpc_core::DebugOnlyTraceFlag grpc_combiner_trace(false, "combiner");
37
38 #define GRPC_COMBINER_TRACE(fn) \
39 do { \
40 if (grpc_combiner_trace.enabled()) { \
41 fn; \
42 } \
43 } while (0)
44
45 #define STATE_UNORPHANED 1
46 #define STATE_ELEM_COUNT_LOW_BIT 2
47
48 static void combiner_exec(grpc_core::Combiner* lock, grpc_closure* closure,
49 grpc_error_handle error);
50 static void combiner_finally_exec(grpc_core::Combiner* lock,
51 grpc_closure* closure,
52 grpc_error_handle error);
53
54 static void offload(void* arg, grpc_error_handle error);
55
grpc_combiner_create(void)56 grpc_core::Combiner* grpc_combiner_create(void) {
57 grpc_core::Combiner* lock = new grpc_core::Combiner();
58 gpr_ref_init(&lock->refs, 1);
59 gpr_atm_no_barrier_store(&lock->state, STATE_UNORPHANED);
60 grpc_closure_list_init(&lock->final_list);
61 GRPC_CLOSURE_INIT(&lock->offload, offload, lock, nullptr);
62 GRPC_COMBINER_TRACE(gpr_log(GPR_INFO, "C:%p create", lock));
63 return lock;
64 }
65
really_destroy(grpc_core::Combiner * lock)66 static void really_destroy(grpc_core::Combiner* lock) {
67 GRPC_COMBINER_TRACE(gpr_log(GPR_INFO, "C:%p really_destroy", lock));
68 GPR_ASSERT(gpr_atm_no_barrier_load(&lock->state) == 0);
69 delete lock;
70 }
71
start_destroy(grpc_core::Combiner * lock)72 static void start_destroy(grpc_core::Combiner* lock) {
73 gpr_atm old_state = gpr_atm_full_fetch_add(&lock->state, -STATE_UNORPHANED);
74 GRPC_COMBINER_TRACE(gpr_log(
75 GPR_INFO, "C:%p really_destroy old_state=%" PRIdPTR, lock, old_state));
76 if (old_state == 1) {
77 really_destroy(lock);
78 }
79 }
80
81 #ifndef NDEBUG
82 #define GRPC_COMBINER_DEBUG_SPAM(op, delta) \
83 if (grpc_combiner_trace.enabled()) { \
84 gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, \
85 "C:%p %s %" PRIdPTR " --> %" PRIdPTR " %s", lock, (op), \
86 gpr_atm_no_barrier_load(&lock->refs.count), \
87 gpr_atm_no_barrier_load(&lock->refs.count) + (delta), reason); \
88 }
89 #else
90 #define GRPC_COMBINER_DEBUG_SPAM(op, delta)
91 #endif
92
grpc_combiner_unref(grpc_core::Combiner * lock GRPC_COMBINER_DEBUG_ARGS)93 void grpc_combiner_unref(grpc_core::Combiner* lock GRPC_COMBINER_DEBUG_ARGS) {
94 GRPC_COMBINER_DEBUG_SPAM("UNREF", -1);
95 if (gpr_unref(&lock->refs)) {
96 start_destroy(lock);
97 }
98 }
99
grpc_combiner_ref(grpc_core::Combiner * lock GRPC_COMBINER_DEBUG_ARGS)100 grpc_core::Combiner* grpc_combiner_ref(
101 grpc_core::Combiner* lock GRPC_COMBINER_DEBUG_ARGS) {
102 GRPC_COMBINER_DEBUG_SPAM(" REF", 1);
103 gpr_ref(&lock->refs);
104 return lock;
105 }
106
push_last_on_exec_ctx(grpc_core::Combiner * lock)107 static void push_last_on_exec_ctx(grpc_core::Combiner* lock) {
108 lock->next_combiner_on_this_exec_ctx = nullptr;
109 if (grpc_core::ExecCtx::Get()->combiner_data()->active_combiner == nullptr) {
110 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner =
111 grpc_core::ExecCtx::Get()->combiner_data()->last_combiner = lock;
112 } else {
113 grpc_core::ExecCtx::Get()
114 ->combiner_data()
115 ->last_combiner->next_combiner_on_this_exec_ctx = lock;
116 grpc_core::ExecCtx::Get()->combiner_data()->last_combiner = lock;
117 }
118 }
119
push_first_on_exec_ctx(grpc_core::Combiner * lock)120 static void push_first_on_exec_ctx(grpc_core::Combiner* lock) {
121 lock->next_combiner_on_this_exec_ctx =
122 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner;
123 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner = lock;
124 if (lock->next_combiner_on_this_exec_ctx == nullptr) {
125 grpc_core::ExecCtx::Get()->combiner_data()->last_combiner = lock;
126 }
127 }
128
combiner_exec(grpc_core::Combiner * lock,grpc_closure * cl,grpc_error_handle error)129 static void combiner_exec(grpc_core::Combiner* lock, grpc_closure* cl,
130 grpc_error_handle error) {
131 GPR_TIMER_SCOPE("combiner.execute", 0);
132 GRPC_STATS_INC_COMBINER_LOCKS_SCHEDULED_ITEMS();
133 gpr_atm last = gpr_atm_full_fetch_add(&lock->state, STATE_ELEM_COUNT_LOW_BIT);
134 GRPC_COMBINER_TRACE(gpr_log(GPR_INFO,
135 "C:%p grpc_combiner_execute c=%p last=%" PRIdPTR,
136 lock, cl, last));
137 if (last == 1) {
138 GRPC_STATS_INC_COMBINER_LOCKS_INITIATED();
139 GPR_TIMER_MARK("combiner.initiated", 0);
140 gpr_atm_no_barrier_store(&lock->initiating_exec_ctx_or_null,
141 (gpr_atm)grpc_core::ExecCtx::Get());
142 // first element on this list: add it to the list of combiner locks
143 // executing within this exec_ctx
144 push_last_on_exec_ctx(lock);
145 } else {
146 // there may be a race with setting here: if that happens, we may delay
147 // offload for one or two actions, and that's fine
148 gpr_atm initiator =
149 gpr_atm_no_barrier_load(&lock->initiating_exec_ctx_or_null);
150 if (initiator != 0 &&
151 initiator != reinterpret_cast<gpr_atm>(grpc_core::ExecCtx::Get())) {
152 gpr_atm_no_barrier_store(&lock->initiating_exec_ctx_or_null, 0);
153 }
154 }
155 GPR_ASSERT(last & STATE_UNORPHANED); // ensure lock has not been destroyed
156 assert(cl->cb);
157 cl->error_data.error = error;
158 lock->queue.Push(cl->next_data.mpscq_node.get());
159 }
160
move_next()161 static void move_next() {
162 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner =
163 grpc_core::ExecCtx::Get()
164 ->combiner_data()
165 ->active_combiner->next_combiner_on_this_exec_ctx;
166 if (grpc_core::ExecCtx::Get()->combiner_data()->active_combiner == nullptr) {
167 grpc_core::ExecCtx::Get()->combiner_data()->last_combiner = nullptr;
168 }
169 }
170
offload(void * arg,grpc_error_handle)171 static void offload(void* arg, grpc_error_handle /*error*/) {
172 grpc_core::Combiner* lock = static_cast<grpc_core::Combiner*>(arg);
173 push_last_on_exec_ctx(lock);
174 }
175
queue_offload(grpc_core::Combiner * lock)176 static void queue_offload(grpc_core::Combiner* lock) {
177 GRPC_STATS_INC_COMBINER_LOCKS_OFFLOADED();
178 move_next();
179 GRPC_COMBINER_TRACE(gpr_log(GPR_INFO, "C:%p queue_offload", lock));
180 grpc_core::Executor::Run(&lock->offload, GRPC_ERROR_NONE);
181 }
182
grpc_combiner_continue_exec_ctx()183 bool grpc_combiner_continue_exec_ctx() {
184 GPR_TIMER_SCOPE("combiner.continue_exec_ctx", 0);
185 grpc_core::Combiner* lock =
186 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner;
187 if (lock == nullptr) {
188 return false;
189 }
190
191 bool contended =
192 gpr_atm_no_barrier_load(&lock->initiating_exec_ctx_or_null) == 0;
193
194 GRPC_COMBINER_TRACE(gpr_log(GPR_INFO,
195 "C:%p grpc_combiner_continue_exec_ctx "
196 "contended=%d "
197 "exec_ctx_ready_to_finish=%d "
198 "time_to_execute_final_list=%d",
199 lock, contended,
200 grpc_core::ExecCtx::Get()->IsReadyToFinish(),
201 lock->time_to_execute_final_list));
202
203 // offload only if all the following conditions are true:
204 // 1. the combiner is contended and has more than one closure to execute
205 // 2. the current execution context needs to finish as soon as possible
206 // 3. the current thread is not a worker for any background poller
207 // 4. the DEFAULT executor is threaded
208 if (contended && grpc_core::ExecCtx::Get()->IsReadyToFinish() &&
209 !grpc_iomgr_is_any_background_poller_thread() &&
210 grpc_core::Executor::IsThreadedDefault()) {
211 GPR_TIMER_MARK("offload_from_finished_exec_ctx", 0);
212 // this execution context wants to move on: schedule remaining work to be
213 // picked up on the executor
214 queue_offload(lock);
215 return true;
216 }
217
218 if (!lock->time_to_execute_final_list ||
219 // peek to see if something new has shown up, and execute that with
220 // priority
221 (gpr_atm_acq_load(&lock->state) >> 1) > 1) {
222 grpc_core::MultiProducerSingleConsumerQueue::Node* n = lock->queue.Pop();
223 GRPC_COMBINER_TRACE(
224 gpr_log(GPR_INFO, "C:%p maybe_finish_one n=%p", lock, n));
225 if (n == nullptr) {
226 // queue is in an inconsistent state: use this as a cue that we should
227 // go off and do something else for a while (and come back later)
228 GPR_TIMER_MARK("delay_busy", 0);
229 queue_offload(lock);
230 return true;
231 }
232 GPR_TIMER_SCOPE("combiner.exec1", 0);
233 grpc_closure* cl = reinterpret_cast<grpc_closure*>(n);
234 grpc_error_handle cl_err = cl->error_data.error;
235 #ifndef NDEBUG
236 cl->scheduled = false;
237 #endif
238 cl->cb(cl->cb_arg, cl_err);
239 GRPC_ERROR_UNREF(cl_err);
240 } else {
241 grpc_closure* c = lock->final_list.head;
242 GPR_ASSERT(c != nullptr);
243 grpc_closure_list_init(&lock->final_list);
244 int loops = 0;
245 while (c != nullptr) {
246 GPR_TIMER_SCOPE("combiner.exec_1final", 0);
247 GRPC_COMBINER_TRACE(
248 gpr_log(GPR_INFO, "C:%p execute_final[%d] c=%p", lock, loops, c));
249 grpc_closure* next = c->next_data.next;
250 grpc_error_handle error = c->error_data.error;
251 #ifndef NDEBUG
252 c->scheduled = false;
253 #endif
254 c->cb(c->cb_arg, error);
255 GRPC_ERROR_UNREF(error);
256 c = next;
257 }
258 }
259
260 GPR_TIMER_MARK("unref", 0);
261 move_next();
262 lock->time_to_execute_final_list = false;
263 gpr_atm old_state =
264 gpr_atm_full_fetch_add(&lock->state, -STATE_ELEM_COUNT_LOW_BIT);
265 GRPC_COMBINER_TRACE(
266 gpr_log(GPR_INFO, "C:%p finish old_state=%" PRIdPTR, lock, old_state));
267 // Define a macro to ease readability of the following switch statement.
268 #define OLD_STATE_WAS(orphaned, elem_count) \
269 (((orphaned) ? 0 : STATE_UNORPHANED) | \
270 ((elem_count)*STATE_ELEM_COUNT_LOW_BIT))
271 // Depending on what the previous state was, we need to perform different
272 // actions.
273 switch (old_state) {
274 default:
275 // we have multiple queued work items: just continue executing them
276 break;
277 case OLD_STATE_WAS(false, 2):
278 case OLD_STATE_WAS(true, 2):
279 // we're down to one queued item: if it's the final list we should do that
280 if (!grpc_closure_list_empty(lock->final_list)) {
281 lock->time_to_execute_final_list = true;
282 }
283 break;
284 case OLD_STATE_WAS(false, 1):
285 // had one count, one unorphaned --> unlocked unorphaned
286 return true;
287 case OLD_STATE_WAS(true, 1):
288 // and one count, one orphaned --> unlocked and orphaned
289 really_destroy(lock);
290 return true;
291 case OLD_STATE_WAS(false, 0):
292 case OLD_STATE_WAS(true, 0):
293 // these values are illegal - representing an already unlocked or
294 // deleted lock
295 GPR_UNREACHABLE_CODE(return true);
296 }
297 push_first_on_exec_ctx(lock);
298 return true;
299 }
300
301 static void enqueue_finally(void* closure, grpc_error_handle error);
302
combiner_finally_exec(grpc_core::Combiner * lock,grpc_closure * closure,grpc_error_handle error)303 static void combiner_finally_exec(grpc_core::Combiner* lock,
304 grpc_closure* closure,
305 grpc_error_handle error) {
306 GPR_ASSERT(lock != nullptr);
307 GPR_TIMER_SCOPE("combiner.execute_finally", 0);
308 GRPC_STATS_INC_COMBINER_LOCKS_SCHEDULED_FINAL_ITEMS();
309 GRPC_COMBINER_TRACE(gpr_log(
310 GPR_INFO, "C:%p grpc_combiner_execute_finally c=%p; ac=%p", lock, closure,
311 grpc_core::ExecCtx::Get()->combiner_data()->active_combiner));
312 if (grpc_core::ExecCtx::Get()->combiner_data()->active_combiner != lock) {
313 GPR_TIMER_MARK("slowpath", 0);
314 // Using error_data.scratch to store the combiner so that it can be accessed
315 // in enqueue_finally.
316 closure->error_data.scratch = reinterpret_cast<uintptr_t>(lock);
317 lock->Run(GRPC_CLOSURE_CREATE(enqueue_finally, closure, nullptr), error);
318 return;
319 }
320
321 if (grpc_closure_list_empty(lock->final_list)) {
322 gpr_atm_full_fetch_add(&lock->state, STATE_ELEM_COUNT_LOW_BIT);
323 }
324 grpc_closure_list_append(&lock->final_list, closure, error);
325 }
326
enqueue_finally(void * closure,grpc_error_handle error)327 static void enqueue_finally(void* closure, grpc_error_handle error) {
328 grpc_closure* cl = static_cast<grpc_closure*>(closure);
329 combiner_finally_exec(
330 reinterpret_cast<grpc_core::Combiner*>(cl->error_data.scratch), cl,
331 GRPC_ERROR_REF(error));
332 }
333
334 namespace grpc_core {
Run(grpc_closure * closure,grpc_error_handle error)335 void Combiner::Run(grpc_closure* closure, grpc_error_handle error) {
336 combiner_exec(this, closure, error);
337 }
338
FinallyRun(grpc_closure * closure,grpc_error_handle error)339 void Combiner::FinallyRun(grpc_closure* closure, grpc_error_handle error) {
340 combiner_finally_exec(this, closure, error);
341 }
342 } // namespace grpc_core
343