[Feature] Support Idle Callback in TaskGroup for flexibility usage

src/bthread/bthread.cpp

@@ -30,6 +30,7 @@
 #include "bthread/timer_thread.h"
 #include "bthread/list_of_abafree_id.h"
 #include "bthread/bthread.h"
+#include "bthread/worker_idle.h"
 
 namespace bthread {
 extern void print_task(std::ostream& os, bthread_t tid, bool enable_trace,
@@ -597,6 +598,17 @@ int bthread_set_tagged_worker_startfn(void (*start_fn)(bthread_tag_t)) {
     return 0;
 }
 
+int bthread_register_worker_idle_function(int (*init_fn)(void),
+                                          bool (*idle_fn)(void),
+                                          uint64_t timeout_us,
+                                          int* handle) {
+    return bthread::register_worker_idle_function(init_fn, idle_fn, timeout_us, handle);
+}
+
+int bthread_unregister_worker_idle_function(int handle) {
+    return bthread::unregister_worker_idle_function(handle);
+}
+
 int bthread_set_create_span_func(void* (*func)()) {
     if (func == NULL) {
         return EINVAL;

src/bthread/parking_lot.h

@@ -64,15 +64,15 @@ class BAIDU_CACHELINE_ALIGNMENT ParkingLot {
 
     // Wait for tasks.
     // If the `expected_state' does not match, wait() may finish directly.
-    void wait(const State& expected_state) {
+    void wait(const State& expected_state, const timespec* timeout = NULL) {
         if (get_state().val != expected_state.val) {
             // Fast path, no need to futex_wait.
             return;
         }
         if (_no_signal_when_no_waiter) {
             _waiter_num.fetch_add(1, butil::memory_order_relaxed);
         }
-        futex_wait_private(&_pending_signal, expected_state.val, NULL);
+        futex_wait_private(&_pending_signal, expected_state.val, timeout);
         if (_no_signal_when_no_waiter) {
             _waiter_num.fetch_sub(1, butil::memory_order_relaxed);
         }

src/bthread/task_group.cpp

@@ -37,6 +37,7 @@
 #include "bthread/task_group.h"
 #include "bthread/timer_thread.h"
 #include "bthread/bthread.h"
+#include "bthread/worker_idle.h"
 
 #ifdef __x86_64__
 #include <x86intrin.h>
@@ -167,7 +168,10 @@ bool TaskGroup::wait_task(bthread_t* tid) {
         if (_last_pl_state.stopped()) {
             return false;
         }
-        _pl->wait(_last_pl_state);
+        run_worker_idle_functions();
+        const timespec timeout = get_worker_idle_timeout();
+        const bool empty_time = (timeout.tv_sec == 0 && timeout.tv_nsec == 0);
+        _pl->wait(_last_pl_state, empty_time ? NULL : &timeout);
         if (steal_task(tid)) {
             return true;
         }
@@ -176,10 +180,13 @@ bool TaskGroup::wait_task(bthread_t* tid) {
         if (st.stopped()) {
             return false;
         }
+        run_worker_idle_functions();
         if (steal_task(tid)) {
             return true;
         }
-        _pl->wait(st);
+        const timespec timeout = get_worker_idle_timeout();
+        const bool empty_time = (timeout.tv_sec == 0 && timeout.tv_nsec == 0);
+        _pl->wait(st, empty_time ? NULL : &timeout);
 #endif
     } while (true);
 }

src/bthread/unstable.h

@@ -92,6 +92,46 @@ extern int bthread_set_worker_startfn(void (*start_fn)());
 // Add a startup function with tag
 extern int bthread_set_tagged_worker_startfn(void (*start_fn)(bthread_tag_t));
 
+// Registers a per-worker init function and an idle function.
+//
+// The init function is called at most once per worker thread, before the first
+// invocation of idle_fn in that worker.
+//
+// The idle function is called when a worker has no task to run.
+// The return value of idle_fn is ignored.
+// If no idle function is registered, the worker waits indefinitely. Otherwise
+// the worker waits for at most the minimal timeout among registered functions
+// before trying again.
+//
+// This function is thread-safe.
+//
+// Args:
+//   init_fn: Optional. Called once per worker thread. Return 0 on success. A
+//            non-zero return value disables idle_fn for that worker thread.
+//   idle_fn: Required. Must not be NULL. Return true if any work is done.
+//   timeout_us: Required. Must be > 0. Maximum waiting time when worker is idle.
+//   handle: Optional output. On success, set to a positive handle for later
+//           unregistration.
+//
+// Returns:
+//   0 on success, error code otherwise.
+extern int bthread_register_worker_idle_function(int (*init_fn)(void),
+                                                 bool (*idle_fn)(void),
+                                                 uint64_t timeout_us,
+                                                 int* handle);
+
+// Unregisters an idle function by handle returned by
+// bthread_register_worker_idle_function().
+//
+// This function is thread-safe.
+//
+// Args:
+//   handle: Handle returned by bthread_register_worker_idle_function().
+//
+// Returns:
+//   0 on success, error code otherwise.
+extern int bthread_unregister_worker_idle_function(int handle);
+
 // Add a create span function
 extern int bthread_set_create_span_func(void* (*func)());
 

src/bthread/worker_idle.cpp

@@ -0,0 +1,188 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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 "bthread/worker_idle.h"
+
+#include <errno.h>
+
+#include <algorithm>
+#include <new>
+#include <vector>
+
+#include "butil/atomicops.h"
+#include "butil/containers/doubly_buffered_data.h"
+#include "butil/time.h"
+#include "butil/thread_local.h"
+
+namespace bthread {
+namespace {
+
+enum InitState : uint8_t {
+    INIT_STATE_NOT_RUN = 0,
+    INIT_STATE_OK = 1,
+    INIT_STATE_FAILED = 2,
+};
+
+struct WorkerIdleEntry {
+    int id;
+    int (*init_fn)(void);
+    bool (*idle_fn)(void);
+    uint64_t timeout_us;
+};
+
+typedef std::vector<WorkerIdleEntry> WorkerIdleEntryList;
+
+static butil::DoublyBufferedData<WorkerIdleEntryList, butil::Void, true> g_entries;
+static butil::atomic<int> g_next_id(1);
+
+struct WorkerIdleTLS {
+    std::vector<uint8_t> init_states;
+};
+
+BAIDU_THREAD_LOCAL WorkerIdleTLS* tls_worker_idle = NULL;
+
+static WorkerIdleTLS* get_or_create_tls() {
+    if (tls_worker_idle) {
+        return tls_worker_idle;
+    }
+    tls_worker_idle = new (std::nothrow) WorkerIdleTLS;
+    return tls_worker_idle;
+}
+
+}  // namespace
+
+int register_worker_idle_function(int (*init_fn)(void),
+                                  bool (*idle_fn)(void),
+                                  uint64_t timeout_us,
+                                  int* handle) {
+    if (idle_fn == NULL) {
+        return EINVAL;
+    }
+    if (timeout_us == 0) {
+        return EINVAL;
+    }
+    const int id = g_next_id.fetch_add(1, butil::memory_order_relaxed);
+    WorkerIdleEntry e;
+    e.id = id;
+    e.init_fn = init_fn;
+    e.idle_fn = idle_fn;
+    e.timeout_us = timeout_us;
+    g_entries.Modify([&](WorkerIdleEntryList& bg) {
+        bg.push_back(e);
+        return static_cast<size_t>(1);
+    });
+    if (handle) {
+        *handle = id;
+    }
+    return 0;
+}
+
+int unregister_worker_idle_function(int handle) {
+    if (handle <= 0) {
+        return EINVAL;
+    }
+    size_t removed = g_entries.Modify([&](WorkerIdleEntryList& bg) {
+        const size_t old_size = bg.size();
+        bg.erase(std::remove_if(bg.begin(), bg.end(),
+                                [&](const WorkerIdleEntry& e) {
+                                    return e.id == handle;
+                                }),
+                 bg.end());
+        return old_size - bg.size();
+    });
+    return removed ? 0 : EINVAL;
+}
+
+bool has_worker_idle_functions() {
+    butil::DoublyBufferedData<WorkerIdleEntryList, butil::Void, true>::ScopedPtr p;
+    if (g_entries.Read(&p) != 0) {
+        return false;
+    }
+    return !p->empty();
+}
+
+void run_worker_idle_functions() {
+    if (!has_worker_idle_functions()) {
+        return;
+    }
+    butil::DoublyBufferedData<WorkerIdleEntryList, butil::Void, true>::ScopedPtr p;
+    if (g_entries.Read(&p) != 0) {
+        return;
+    }
+    if (p->empty()) {
+        return;
+    }
+
+    WorkerIdleTLS* tls = get_or_create_tls();
+    if (tls == NULL) {
+        return;
+    }
+
+    // Step 1: Ensure per-worker init is called at most once for each entry.
+    // Step 2: Run idle callbacks for initialized entries.
+    // Step 3: Ignore callback return values. The caller decides how to proceed.
+    for (const auto& e : *p) {
+        if (e.id <= 0 || e.idle_fn == NULL) {
+            continue;
+        }
+        if (tls->init_states.size() <= static_cast<size_t>(e.id)) {
+            tls->init_states.resize(static_cast<size_t>(e.id) + 1, INIT_STATE_NOT_RUN);
+        }
+        uint8_t& st = tls->init_states[static_cast<size_t>(e.id)];
+        if (st == INIT_STATE_NOT_RUN) {
+            // Run the init callback function once.
+            if (e.init_fn) {
+                const int rc = e.init_fn();
+                st = (rc == 0) ? INIT_STATE_OK : INIT_STATE_FAILED;
+            } else {
+                st = INIT_STATE_OK;
+            }
+        }
+        if (st != INIT_STATE_OK) {
+            continue;
+        }
+        // Run the idle callback function.
+        e.idle_fn();
+    }
+}
+
+timespec get_worker_idle_timeout() {
+    butil::DoublyBufferedData<WorkerIdleEntryList, butil::Void, true>::ScopedPtr p;
+    if (g_entries.Read(&p) != 0) {
+        return {0, 0};
+    }
+    if (p->empty()) {
+        return {0, 0};
+    }
+    uint64_t min_us = 0;
+    for (const auto& e : *p) {
+        if (e.timeout_us == 0) {
+            continue;
+        }
+        if (min_us == 0 || e.timeout_us < min_us) {
+            min_us = e.timeout_us;
+        }
+    }
+    if (min_us == 0) {
+        return {0, 0};
+    }
+    return butil::microseconds_to_timespec(min_us);
+}
+
+}  // namespace bthread
+
+

src/bthread/worker_idle.h

@@ -0,0 +1,67 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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 BTHREAD_WORKER_IDLE_H
+#define BTHREAD_WORKER_IDLE_H
+
+#include <stdint.h>
+#include <time.h>
+
+namespace bthread {
+
+// Registers a per-worker init function and an idle function.
+//
+// The init function is called at most once per worker thread, before running
+// the idle function in that worker thread.
+//
+// Args:
+//   init_fn: Optional. Can be NULL.
+//   idle_fn: Required. Must not be NULL.
+//   timeout_us: Required. Must be > 0.
+//   handle: Optional output handle for unregistering later.
+//
+// Returns:
+//   0 on success, error code otherwise.
+int register_worker_idle_function(int (*init_fn)(void),
+                                  bool (*idle_fn)(void),
+                                  uint64_t timeout_us,
+                                  int* handle);
+
+// Unregisters a previously registered idle function by handle.
+//
+// Args:
+//   handle: Handle returned by register_worker_idle_function().
+//
+// Returns:
+//   0 on success, error code otherwise.
+int unregister_worker_idle_function(int handle);
+
+// Returns true if any idle function is registered.
+bool has_worker_idle_functions();
+
+// Runs all registered idle functions for current worker thread.
+void run_worker_idle_functions();
+
+// Get the minimal timeout among all registered functions.
+// Returns {0,0} if no idle function is registered.
+timespec get_worker_idle_timeout();
+
+}  // namespace bthread
+
+#endif  // BTHREAD_WORKER_IDLE_H
+
+