這是一個(gè)錯(cuò)誤.我已經(jīng)能夠通過在task_io_service :: do_poll_one的非關(guān)鍵部分添加延遲來復(fù)制它.以下是

booost/asio/detail/impl/task_io_service.ipp中修改后的task_io_service :: do_poll_one()的片段.添加的唯一行是sleep.

std::size_t task_io_service::do_poll_one(mutex::scoped_lock& lock,task_io_service::thread_info& this_thread,const boost::system::error_code& ec)

{

if (stopped_)

return 0;

operation* o = op_queue_.front();

if (o == &task_operation_)

{

op_queue_.pop();

lock.unlock();

{

task_cleanup c = { this,&lock,&this_thread };

(void)c;

// Run the task. May throw an exception. Only block if the operation

// queue is empty and we're not polling,otherwise we want to return

// as soon as possible.

task_->run(false,this_thread.private_op_queue);

boost::this_thread::sleep_for(boost::chrono::seconds(3));

}

o = op_queue_.front();

if (o == &task_operation_)

return 0;

}

...

我的測(cè)試驅(qū)動(dòng)程序非常基礎(chǔ)：

>通過計(jì)時(shí)器進(jìn)行異步工作循環(huán),打印“.”每3秒鐘一次.

>生成一個(gè)將輪詢io_service的線程.

>延遲允許新線程時(shí)間輪詢io_service,并且當(dāng)poll線程在task_io_service :: do_poll_one()中休眠時(shí),主調(diào)用io_service :: run().

測(cè)試代碼：

#include

#include

#include

#include

#include

boost::asio::io_service io_service;

boost::asio::steady_timer timer(io_service);

void arm_timer()

{

std::cout << ".";

std::cout.flush();

timer.expires_from_now(boost::chrono::seconds(3));

timer.async_wait(boost::bind(&arm_timer));

}

int main()

{

// Add asynchronous work loop.

arm_timer();

// Spawn poll thread.

boost::thread poll_thread(

boost::bind(&boost::asio::io_service::poll,boost::ref(io_service)));

// Give time for poll thread service reactor.

boost::this_thread::sleep_for(boost::chrono::seconds(1));

io_service.run();

}

調(diào)試：

[twsansbury@localhost bug]$gdb a.out

...

(gdb) r

Starting program: /home/twsansbury/dev/bug/a.out

[Thread debugging using libthread_db enabled]

.[New Thread 0xb7feeb90 (LWP 31892)]

[Thread 0xb7feeb90 (LWP 31892) exited]

此時(shí),arm_timer()已打印“.”曾經(jīng)(當(dāng)它被武裝起來時(shí)). poll線程以非阻塞方式為反應(yīng)器提供服務(wù),并且在op_queue_為空時(shí)睡眠3秒(當(dāng)task_cleanup c退出范圍時(shí),task_operation_將被添加回op_queue_).當(dāng)op_queue_為空時(shí),主線程調(diào)用io_service :: run(),看到op_queue_為空,并使自己成為first_idle_thread_,它在wakeup_event上等待. poll線程完成休眠,并返回0,主線程等待wakeup_event.

等待10秒后,arm_timer()有足夠的時(shí)間準(zhǔn)備就緒,我打斷調(diào)試器：

Program received signal SIGINT,Interrupt.

0x00919402 in __kernel_vsyscall ()

(gdb) bt

#0 0x00919402 in __kernel_vsyscall ()

#1 0x0081bbc5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0

#2 0x00763b3d in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libc.so.6

#3 0x08059dc2 in void boost::asio::detail::posix_event::wait >(boost::asio::detail::scoped_lock&) ()

#4 0x0805a009 in boost::asio::detail::task_io_service::do_run_one(boost::asio::detail::scoped_lock&,boost::asio::detail::task_io_service_thread_info&,boost::system::error_code const&) ()

#5 0x0805a11c in boost::asio::detail::task_io_service::run(boost::system::error_code&) ()

#6 0x0805a1e2 in boost::asio::io_service::run() ()

#7 0x0804db78 in main ()

并排時(shí)間表如下：

poll thread | main thread

---------------------------------------+---------------------------------------

lock() |

do_poll_one() |

|-- pop task_operation_ from |

| queue_op_ |

|-- unlock() | lock()

|-- create task_cleanup | do_run_one()

|-- service reactor (non-block) | `-- queue_op_ is empty

|-- ~task_cleanup() | |-- set thread as idle

| |-- lock() | `-- unlock()

| `-- queue_op_.push( |

| task_operation_) |

`-- task_operation_ is |

queue_op_.front() |

`-- return 0 | // still waiting on wakeup_event

unlock() |

盡我所知,修補(bǔ)沒有副作用：

if (o == &task_operation_)

return 0;

至：

if (o == &task_operation_)

{

if (!one_thread_)

wake_one_thread_and_unlock(lock);

return 0;

}

無論如何,我已經(jīng)提交了bug and fix.考慮留意官方回復(fù)的機(jī)票.

總結(jié)

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