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I wrote a proxy service program that used boost asio, the proxy server has two socket(client_socket_,server_socket_)，If one of the socket is disconnected another one to remain active。For example, if read from client_socket_ results in error, i will close client_socket_ and then wait for client to reconnect and after client reconnects, I read from one socket and write to another.

The problem is that, when i close the client_socket_ how to cancel the asynchronous operation in server_socket_? if i do not do this, the previous asynchronous operation will execute after client connected. The follow is handler tracking, handler 19 is need to cancel.

E:\code\vdoctor-r\code\dnc\Debug>forwardserver.exe
@asio|1337591080.941830|0*1|socket@0012FA58.async_accept
@asio|1337591107.009440|>1|ec=system:0
@asio|1337591107.009440|1*2|strand@003E8340.dispatch
@asio|1337591107.009440|>2|
@asio|1337591107.009440|2*3|socket@0012FAB0.async_connect
@asio|1337591107.025059|2*4|socket@0012FA58.async_accept
@asio|1337591107.025059|<2|
@asio|1337591107.025059|<1|
@asio|1337591107.025059|>3|ec=system:0
@asio|1337591107.025059|3*5|strand@003E8340.dispatch
@asio|1337591107.025059|>5|
2012-May-21 17:05:07 [info]-[e:\code\vdoctor-r\code\dnc\forwardserver\forward_se
rver.cpp(114):forward_server::handle_connect_to_server] connect to server succes
sful, start to receive data from both sides
@asio|1337591107.040678|5*6|socket@003E83D4.async_receive
@asio|1337591107.040678|5*7|socket@0012FAB0.async_receive
@asio|1337591107.040678|<5|
@asio|1337591107.040678|<3|
@asio|1337591107.040678|>6|ec=system:0,bytes_transferred=20
@asio|1337591107.040678|6*8|strand@003E8340.dispatch
@asio|1337591107.040678|>8|
@asio|1337591107.040678|8*9|socket@003E83D4.async_receive
@asio|1337591107.040678|<8|
@asio|1337591107.040678|<6|
@asio|1337591107.040678|>9|ec=system:0,bytes_transferred=17
@asio|1337591107.040678|9*10|strand@003E8340.dispatch
@asio|1337591107.040678|>10|
@asio|1337591107.040678|10*11|socket@0012FAB0.async_send
@asio|1337591107.056296|<10|
@asio|1337591107.056296|<9|
@asio|1337591107.056296|>11|ec=system:0,bytes_transferred=37
@asio|1337591107.056296|11*12|strand@003E8340.dispatch
@asio|1337591107.056296|>12|
@asio|1337591107.056296|12*13|socket@003E83D4.async_receive
@asio|1337591107.056296|<12|
@asio|1337591107.056296|<11|
@asio|1337591107.071915|>7|ec=system:0,bytes_transferred=20
@asio|1337591107.071915|7*14|strand@003E8340.dispatch
@asio|1337591107.071915|>14|
@asio|1337591107.071915|14*15|socket@0012FAB0.async_receive
@asio|1337591107.071915|<14|
@asio|1337591107.071915|<7|
@asio|1337591107.071915|>15|ec=system:0,bytes_transferred=18
@asio|1337591107.071915|15*16|strand@003E8340.dispatch
@asio|1337591107.071915|>16|
@asio|1337591107.071915|16*17|socket@003E83D4.async_send
@asio|1337591107.071915|<16|
@asio|1337591107.071915|<15|
@asio|1337591107.087534|>17|ec=system:0,bytes_transferred=38
@asio|1337591107.087534|17*18|strand@003E8340.dispatch
@asio|1337591107.087534|>18|
@asio|1337591107.087534|18*19|socket@0012FAB0.async_receive
@asio|1337591107.087534|<18|
@asio|1337591107.087534|<17|
@asio|1337591107.884087|>13|ec=asio.misc:2,bytes_transferred=0
@asio|1337591107.884087|13*20|strand@003E8340.dispatch
@asio|1337591107.884087|>20|
2012-May-21 17:05:07 [error]-[e:\code\vdoctor-r\code\dnc\forwardserver\forward_s
erver.cpp(273):forward_server::handle_read_header_from_client] read header from
client error,End of file
@asio|1337591107.884087|20|socket@003E83D4.close
@asio|1337591107.884087|<20|
@asio|1337591107.884087|<13|
@asio|1337591222.813720|>4|ec=system:0
@asio|1337591222.813720|4*21|strand@003E8340.dispatch
@asio|1337591222.813720|>21|
@asio|1337591222.813720|21*22|socket@003ECF2C.async_receive
@asio|1337591222.813720|21*23|socket@0012FAB0.async_receive
@asio|1337591222.813720|21*24|socket@0012FA58.async_accept
@asio|1337591222.813720|<21|
@asio|1337591222.813720|<4|
@asio|1337591222.813720|>22|ec=system:0,bytes_transferred=20
@asio|1337591222.813720|22*25|strand@003E8340.dispatch
@asio|1337591222.813720|>25|
@asio|1337591222.813720|25*26|socket@003ECF2C.async_receive
@asio|1337591222.813720|<25|
@asio|1337591222.813720|<22|
@asio|1337591222.813720|>26|ec=system:0,bytes_transferred=17
@asio|1337591222.813720|26*27|strand@003E8340.dispatch
@asio|1337591222.813720|>27|
@asio|1337591222.813720|27*28|socket@0012FAB0.async_send
@asio|1337591222.813720|<27|
@asio|1337591222.813720|<26|
@asio|1337591222.813720|>28|ec=system:0,bytes_transferred=37
@asio|1337591222.813720|28*29|strand@003E8340.dispatch
@asio|1337591222.813720|>29|
@asio|1337591222.813720|29*30|socket@003ECF2C.async_receive
@asio|1337591222.813720|<29|
@asio|1337591222.813720|<28|
@asio|1337591222.813720|>19|ec=system:0,bytes_transferred=20
@asio|1337591222.813720|19*31|strand@003E8340.dispatch
@asio|1337591222.813720|>31|
@asio|1337591222.813720|31*32|socket@0012FAB0.async_receive
@asio|1337591222.813720|<31|
@asio|1337591222.813720|<19|
@asio|1337591222.813720|>23|ec=system:0,bytes_transferred=18
@asio|1337591222.813720|23*33|strand@003E8340.dispatch
@asio|1337591222.829340|>33|
@asio|1337591222.829340|33*34|socket@0012FAB0.async_receive
@asio|1337591222.829340|<33|
@asio|1337591222.829340|<23|
Sam Miller
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Jayden
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1 Answers1

4

The only portable and reliable way to cancel async.operations on server_socket_ is to close it. See the following link for details.

Sam Miller
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Igor R.
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  • But my intention is not to close the server_socket_,if i define BOOST_ASIO_ENABLE_CANCELIO and call server_socket_.cancel() to cancel previous asynchronous operation but not close server_socket_,can recall asio::async_read(server_socket_, ...) when the client reconnects? – Jayden May 21 '12 at 13:21
  • @Jayden, you can use cancel() if you're fine with the fact that "it can appear to complete without error, but the request to cancel the unfinished operations may be silently ignored by the operating system. Whether it works or not seems to depend on the drivers that are installed". Besides, even if it succeeds, some data may have been read from the server - so you need to invent some way to get re-synchronised with your server. – Igor R. May 21 '12 at 13:37
  • Igor R,thank you for your patience to answer my question,what does this solution mean of "Disable asio's I/O completion port backend by defining BOOST_ASIO_DISABLE_IOCP."? [in this document](http://www.boost.org/doc/libs/1_49_0/doc/html/boost_asio/reference/basic_stream_socket/cancel/overload2.html) I was a novice of boost::asio. – Jayden May 21 '12 at 14:12
  • @Jayden, if you define this macro, ASIO won't use completion ports. Instead it will use the older reactor model (select etc). You can read here [link](http://stackoverflow.com/questions/5283032/i-o-completion-ports-advantages-and-disadvantages) about the advantages of CP. – Igor R. May 21 '12 at 14:21
  • @lgor R, i mean if I use the solution of " defining BOOST_ASIO_DISABLE_IOCP" how to cancel server_socket_'s previous asynchronous operation, like handler 19 as above. thank you! – Jayden May 21 '12 at 14:40
  • @Jayden, if you define BOOST_ASIO_DISABLE_IOCP, cancel() function will work. But again, after such a cancellation your application protocol may remain in some arbitrary state, so you'll have to re-synchronize with your server. – Igor R. May 21 '12 at 14:59
  • The warnings about `socket.cancel()` only apply "when run on Windows XP, Windows Server 2003, and earlier versions of Windows". That may have been a concern when this question was posted in 2012 (mainstream support for both OSs had ended but they were still in extended support) but not today in 2023. Essentially, `socket.cancel()` is usable for any plausible target OS. – Arthur Tacca Jun 19 '23 at 15:05