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Diffstat (limited to 'src/core/lib/gprpp/fork.cc')
| -rw-r--r-- | src/core/lib/gprpp/fork.cc | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/src/core/lib/gprpp/fork.cc b/src/core/lib/gprpp/fork.cc new file mode 100644 index 0000000000..f6d9a87d2c --- /dev/null +++ b/src/core/lib/gprpp/fork.cc @@ -0,0 +1,260 @@ +/* + * + * 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 <grpc/support/port_platform.h> + +#include "src/core/lib/gprpp/fork.h" + +#include <string.h> + +#include <grpc/support/alloc.h> +#include <grpc/support/sync.h> +#include <grpc/support/time.h> + +#include "src/core/lib/gpr/env.h" +#include "src/core/lib/gpr/useful.h" +#include "src/core/lib/gprpp/memory.h" + +/* + * NOTE: FORKING IS NOT GENERALLY SUPPORTED, THIS IS ONLY INTENDED TO WORK + * AROUND VERY SPECIFIC USE CASES. + */ + +namespace grpc_core { +namespace internal { +// The exec_ctx_count has 2 modes, blocked and unblocked. +// When unblocked, the count is 2-indexed; exec_ctx_count=2 indicates +// 0 active ExecCtxs, exex_ctx_count=3 indicates 1 active ExecCtxs... + +// When blocked, the exec_ctx_count is 0-indexed. Note that ExecCtx +// creation can only be blocked if there is exactly 1 outstanding ExecCtx, +// meaning that BLOCKED and UNBLOCKED counts partition the integers +#define UNBLOCKED(n) (n + 2) +#define BLOCKED(n) (n) + +class ExecCtxState { + public: + ExecCtxState() : fork_complete_(true) { + gpr_mu_init(&mu_); + gpr_cv_init(&cv_); + gpr_atm_no_barrier_store(&count_, UNBLOCKED(0)); + } + + void IncExecCtxCount() { + gpr_atm count = gpr_atm_no_barrier_load(&count_); + while (true) { + if (count <= BLOCKED(1)) { + // This only occurs if we are trying to fork. Wait until the fork() + // operation completes before allowing new ExecCtxs. + gpr_mu_lock(&mu_); + if (gpr_atm_no_barrier_load(&count_) <= BLOCKED(1)) { + while (!fork_complete_) { + gpr_cv_wait(&cv_, &mu_, gpr_inf_future(GPR_CLOCK_REALTIME)); + } + } + gpr_mu_unlock(&mu_); + } else if (gpr_atm_no_barrier_cas(&count_, count, count + 1)) { + break; + } + count = gpr_atm_no_barrier_load(&count_); + } + } + + void DecExecCtxCount() { gpr_atm_no_barrier_fetch_add(&count_, -1); } + + bool BlockExecCtx() { + // Assumes there is an active ExecCtx when this function is called + if (gpr_atm_no_barrier_cas(&count_, UNBLOCKED(1), BLOCKED(1))) { + gpr_mu_lock(&mu_); + fork_complete_ = false; + gpr_mu_unlock(&mu_); + return true; + } + return false; + } + + void AllowExecCtx() { + gpr_mu_lock(&mu_); + gpr_atm_no_barrier_store(&count_, UNBLOCKED(0)); + fork_complete_ = true; + gpr_cv_broadcast(&cv_); + gpr_mu_unlock(&mu_); + } + + ~ExecCtxState() { + gpr_mu_destroy(&mu_); + gpr_cv_destroy(&cv_); + } + + private: + bool fork_complete_; + gpr_mu mu_; + gpr_cv cv_; + gpr_atm count_; +}; + +class ThreadState { + public: + ThreadState() : awaiting_threads_(false), threads_done_(false), count_(0) { + gpr_mu_init(&mu_); + gpr_cv_init(&cv_); + } + + void IncThreadCount() { + gpr_mu_lock(&mu_); + count_++; + gpr_mu_unlock(&mu_); + } + + void DecThreadCount() { + gpr_mu_lock(&mu_); + count_--; + if (awaiting_threads_ && count_ == 0) { + threads_done_ = true; + gpr_cv_signal(&cv_); + } + gpr_mu_unlock(&mu_); + } + void AwaitThreads() { + gpr_mu_lock(&mu_); + awaiting_threads_ = true; + threads_done_ = (count_ == 0); + while (!threads_done_) { + gpr_cv_wait(&cv_, &mu_, gpr_inf_future(GPR_CLOCK_REALTIME)); + } + awaiting_threads_ = true; + gpr_mu_unlock(&mu_); + } + + ~ThreadState() { + gpr_mu_destroy(&mu_); + gpr_cv_destroy(&cv_); + } + + private: + bool awaiting_threads_; + bool threads_done_; + gpr_mu mu_; + gpr_cv cv_; + int count_; +}; + +} // namespace + +void Fork::GlobalInit() { + if (!overrideEnabled_) { +#ifdef GRPC_ENABLE_FORK_SUPPORT + supportEnabled_ = true; +#else + supportEnabled_ = false; +#endif + bool env_var_set = false; + char* env = gpr_getenv("GRPC_ENABLE_FORK_SUPPORT"); + if (env != nullptr) { + static const char* truthy[] = {"yes", "Yes", "YES", "true", + "True", "TRUE", "1"}; + static const char* falsey[] = {"no", "No", "NO", "false", + "False", "FALSE", "0"}; + for (size_t i = 0; i < GPR_ARRAY_SIZE(truthy); i++) { + if (0 == strcmp(env, truthy[i])) { + supportEnabled_ = true; + env_var_set = true; + break; + } + } + if (!env_var_set) { + for (size_t i = 0; i < GPR_ARRAY_SIZE(falsey); i++) { + if (0 == strcmp(env, falsey[i])) { + supportEnabled_ = false; + env_var_set = true; + break; + } + } + } + gpr_free(env); + } + } + if (supportEnabled_) { + execCtxState_ = grpc_core::New<internal::ExecCtxState>(); + threadState_ = grpc_core::New<internal::ThreadState>(); + } +} + +void Fork::GlobalShutdown() { + if (supportEnabled_) { + grpc_core::Delete(execCtxState_); + grpc_core::Delete(threadState_); + } +} + +bool Fork::Enabled() { return supportEnabled_; } + +// Testing Only +void Fork::Enable(bool enable) { + overrideEnabled_ = true; + supportEnabled_ = enable; +} + +void Fork::IncExecCtxCount() { + if (supportEnabled_) { + execCtxState_->IncExecCtxCount(); + } +} + +void Fork::DecExecCtxCount() { + if (supportEnabled_) { + execCtxState_->DecExecCtxCount(); + } +} + +bool Fork::BlockExecCtx() { + if (supportEnabled_) { + return execCtxState_->BlockExecCtx(); + } + return false; +} + +void Fork::AllowExecCtx() { + if (supportEnabled_) { + execCtxState_->AllowExecCtx(); + } +} + +void Fork::IncThreadCount() { + if (supportEnabled_) { + threadState_->IncThreadCount(); + } +} + +void Fork::DecThreadCount() { + if (supportEnabled_) { + threadState_->DecThreadCount(); + } +} +void Fork::AwaitThreads() { + if (supportEnabled_) { + threadState_->AwaitThreads(); + } +} + +internal::ExecCtxState* Fork::execCtxState_ = nullptr; +internal::ThreadState* Fork::threadState_ = nullptr; +bool Fork::supportEnabled_ = false; +bool Fork::overrideEnabled_ = false; + +} // namespace grpc_core |