| /* |
| * |
| * 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. |
| * |
| */ |
| |
| #include "src/core/lib/iomgr/lockfree_event.h" |
| |
| #include <grpc/support/log.h> |
| |
| #include "src/core/lib/debug/trace.h" |
| |
| extern grpc_tracer_flag grpc_polling_trace; |
| |
| /* 'state' holds the to call when the fd is readable or writable respectively. |
| It can contain one of the following values: |
| CLOSURE_READY : The fd has an I/O event of interest but there is no |
| closure yet to execute |
| |
| CLOSURE_NOT_READY : The fd has no I/O event of interest |
| |
| closure ptr : The closure to be executed when the fd has an I/O |
| event of interest |
| |
| shutdown_error | FD_SHUTDOWN_BIT : |
| 'shutdown_error' field ORed with FD_SHUTDOWN_BIT. |
| This indicates that the fd is shutdown. Since all |
| memory allocations are word-aligned, the lower two |
| bits of the shutdown_error pointer are always 0. So |
| it is safe to OR these with FD_SHUTDOWN_BIT |
| |
| Valid state transitions: |
| |
| <closure ptr> <-----3------ CLOSURE_NOT_READY ----1----> CLOSURE_READY |
| | | ^ | ^ | | |
| | | | | | | | |
| | +--------------4----------+ 6 +---------2---------------+ | |
| | | | |
| | v | |
| +-----5-------> [shutdown_error | FD_SHUTDOWN_BIT] <----7---------+ |
| |
| For 1, 4 : See grpc_lfev_set_ready() function |
| For 2, 3 : See grpc_lfev_notify_on() function |
| For 5,6,7: See grpc_lfev_set_shutdown() function */ |
| |
| #define CLOSURE_NOT_READY ((gpr_atm)0) |
| #define CLOSURE_READY ((gpr_atm)2) |
| |
| #define FD_SHUTDOWN_BIT ((gpr_atm)1) |
| |
| void grpc_lfev_init(gpr_atm *state) { |
| gpr_atm_no_barrier_store(state, CLOSURE_NOT_READY); |
| } |
| |
| void grpc_lfev_destroy(gpr_atm *state) { |
| gpr_atm curr = gpr_atm_no_barrier_load(state); |
| if (curr & FD_SHUTDOWN_BIT) { |
| GRPC_ERROR_UNREF((grpc_error *)(curr & ~FD_SHUTDOWN_BIT)); |
| } else { |
| GPR_ASSERT(curr == CLOSURE_NOT_READY || curr == CLOSURE_READY); |
| } |
| } |
| |
| bool grpc_lfev_is_shutdown(gpr_atm *state) { |
| gpr_atm curr = gpr_atm_no_barrier_load(state); |
| return (curr & FD_SHUTDOWN_BIT) != 0; |
| } |
| |
| void grpc_lfev_notify_on(grpc_exec_ctx *exec_ctx, gpr_atm *state, |
| grpc_closure *closure, const char *variable) { |
| while (true) { |
| gpr_atm curr = gpr_atm_no_barrier_load(state); |
| if (GRPC_TRACER_ON(grpc_polling_trace)) { |
| gpr_log(GPR_ERROR, "lfev_notify_on[%s]: %p curr=%p closure=%p", variable, |
| state, (void *)curr, closure); |
| } |
| switch (curr) { |
| case CLOSURE_NOT_READY: { |
| /* CLOSURE_NOT_READY -> <closure>. |
| |
| We're guaranteed by API that there's an acquire barrier before here, |
| so there's no need to double-dip and this can be a release-only. |
| |
| The release itself pairs with the acquire half of a set_ready full |
| barrier. */ |
| if (gpr_atm_rel_cas(state, CLOSURE_NOT_READY, (gpr_atm)closure)) { |
| return; /* Successful. Return */ |
| } |
| |
| break; /* retry */ |
| } |
| |
| case CLOSURE_READY: { |
| /* Change the state to CLOSURE_NOT_READY. Schedule the closure if |
| successful. If not, the state most likely transitioned to shutdown. |
| We should retry. |
| |
| This can be a no-barrier cas since the state is being transitioned to |
| CLOSURE_NOT_READY; set_ready and set_shutdown do not schedule any |
| closure when transitioning out of CLOSURE_NO_READY state (i.e there |
| is no other code that needs to 'happen-after' this) */ |
| if (gpr_atm_no_barrier_cas(state, CLOSURE_READY, CLOSURE_NOT_READY)) { |
| GRPC_CLOSURE_SCHED(exec_ctx, closure, GRPC_ERROR_NONE); |
| return; /* Successful. Return */ |
| } |
| |
| break; /* retry */ |
| } |
| |
| default: { |
| /* 'curr' is either a closure or the fd is shutdown(in which case 'curr' |
| contains a pointer to the shutdown-error). If the fd is shutdown, |
| schedule the closure with the shutdown error */ |
| if ((curr & FD_SHUTDOWN_BIT) > 0) { |
| grpc_error *shutdown_err = (grpc_error *)(curr & ~FD_SHUTDOWN_BIT); |
| GRPC_CLOSURE_SCHED(exec_ctx, closure, |
| GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING( |
| "FD Shutdown", &shutdown_err, 1)); |
| return; |
| } |
| |
| /* There is already a closure!. This indicates a bug in the code */ |
| gpr_log(GPR_ERROR, |
| "notify_on called with a previous callback still pending"); |
| abort(); |
| } |
| } |
| } |
| |
| GPR_UNREACHABLE_CODE(return ); |
| } |
| |
| bool grpc_lfev_set_shutdown(grpc_exec_ctx *exec_ctx, gpr_atm *state, |
| grpc_error *shutdown_err) { |
| gpr_atm new_state = (gpr_atm)shutdown_err | FD_SHUTDOWN_BIT; |
| |
| while (true) { |
| gpr_atm curr = gpr_atm_no_barrier_load(state); |
| if (GRPC_TRACER_ON(grpc_polling_trace)) { |
| gpr_log(GPR_ERROR, "lfev_set_shutdown: %p curr=%p err=%s", state, |
| (void *)curr, grpc_error_string(shutdown_err)); |
| } |
| switch (curr) { |
| case CLOSURE_READY: |
| case CLOSURE_NOT_READY: |
| /* Need a full barrier here so that the initial load in notify_on |
| doesn't need a barrier */ |
| if (gpr_atm_full_cas(state, curr, new_state)) { |
| return true; /* early out */ |
| } |
| break; /* retry */ |
| |
| default: { |
| /* 'curr' is either a closure or the fd is already shutdown */ |
| |
| /* If fd is already shutdown, we are done */ |
| if ((curr & FD_SHUTDOWN_BIT) > 0) { |
| GRPC_ERROR_UNREF(shutdown_err); |
| return false; |
| } |
| |
| /* Fd is not shutdown. Schedule the closure and move the state to |
| shutdown state. |
| Needs an acquire to pair with setting the closure (and get a |
| happens-after on that edge), and a release to pair with anything |
| loading the shutdown state. */ |
| if (gpr_atm_full_cas(state, curr, new_state)) { |
| GRPC_CLOSURE_SCHED(exec_ctx, (grpc_closure *)curr, |
| GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING( |
| "FD Shutdown", &shutdown_err, 1)); |
| return true; |
| } |
| |
| /* 'curr' was a closure but now changed to a different state. We will |
| have to retry */ |
| break; |
| } |
| } |
| } |
| |
| GPR_UNREACHABLE_CODE(return false); |
| } |
| |
| void grpc_lfev_set_ready(grpc_exec_ctx *exec_ctx, gpr_atm *state, |
| const char *variable) { |
| while (true) { |
| gpr_atm curr = gpr_atm_no_barrier_load(state); |
| |
| if (GRPC_TRACER_ON(grpc_polling_trace)) { |
| gpr_log(GPR_ERROR, "lfev_set_ready[%s]: %p curr=%p", variable, state, |
| (void *)curr); |
| } |
| |
| switch (curr) { |
| case CLOSURE_READY: { |
| /* Already ready. We are done here */ |
| return; |
| } |
| |
| case CLOSURE_NOT_READY: { |
| /* No barrier required as we're transitioning to a state that does not |
| involve a closure */ |
| if (gpr_atm_no_barrier_cas(state, CLOSURE_NOT_READY, CLOSURE_READY)) { |
| return; /* early out */ |
| } |
| break; /* retry */ |
| } |
| |
| default: { |
| /* 'curr' is either a closure or the fd is shutdown */ |
| if ((curr & FD_SHUTDOWN_BIT) > 0) { |
| /* The fd is shutdown. Do nothing */ |
| return; |
| } |
| /* Full cas: acquire pairs with this cas' release in the event of a |
| spurious set_ready; release pairs with this or the acquire in |
| notify_on (or set_shutdown) */ |
| else if (gpr_atm_full_cas(state, curr, CLOSURE_NOT_READY)) { |
| GRPC_CLOSURE_SCHED(exec_ctx, (grpc_closure *)curr, GRPC_ERROR_NONE); |
| return; |
| } |
| /* else the state changed again (only possible by either a racing |
| set_ready or set_shutdown functions. In both these cases, the closure |
| would have been scheduled for execution. So we are done here */ |
| return; |
| } |
| } |
| } |
| } |