recvfrom for X11-unix socket正在拋出EAGAIN（資源暫時不可用）

Question

我想通過pywebkitgtk捕獲網頁。 我在那台機器上安裝了X org服務器，啟動了X服務器但有一些例外，但X服務器正在運行。 問題是我無法從X unix套接字讀取任何數據，這是PF_FILE類型，路徑= @“/ tmp / .X11-unix / X0”，recvfrom正在拋出EAGAIN（資源暫時不可用）錯誤，輪詢該套接字不斷超時而沒有任何即將到來的數據，下面是跟蹤日志，我們可以在其中找到成功創建的帶有fd 5的unix套接字，連接的unix套接字，到目前為止成功，但無法從該unix套接字讀取任何內容。

developer@kernel: /data/play/null> strace python ../pywebkitgtk-1.1.8/demos/browser.py

socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC, 0) = 5
connect(5, {sa_family=AF_FILE, path=@"/tmp/.X11-unix/X0"}, 20) = 0
getpeername(5, {sa_family=AF_FILE, path=@"/tmp/.X11-unix/X0"}, [20]) = 0


...........................


recvfrom(5, "\1\3\304\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 4096, 0, NULL, NULL) = 32
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"\220\10\7\0\0\1G\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \1", 28}, {NULL, 0}, {"", 0}], 3) = 28
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\3\305\1X\4\0\0\0\0\10\377G\0\0\31\31\0104\1\370\0\0\0\0\0\0\0\0\0\0\10"..., 4096, 0, NULL, NULL) = 4096
recvfrom(5, "\216\377\10\20\0\0\0\0\1\1\1\0\33\377\10\20\0\0\0\0\1\1\1\0_\377\10\20\0\0\0\0"..., 384, 0, NULL, NULL) = 384
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"\220\21\3\0\3\0G\0\0\30\0\0", 12}, {NULL, 0}, {"", 0}], 3) = 12
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\3\306\1\16\0\0\0\0\30\0\0\10\377\31\1\377\37\10\370\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096, 0, NULL, NULL) = 88
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"\20\0\3\0\4\0G\0Meta", 12}, {NULL, 0}, {"", 0}], 3) = 12
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\0\307\1\0\0\0\0\206\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 4096, 0, NULL, NULL) = 32
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"\20\0\4\0\5\0G\0Super\0\0\0", 16}, {NULL, 0}, {"", 0}], 3) = 16
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\0\310\1\0\0\0\0\207\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 4096, 0, NULL, NULL) = 32
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"\20\0\4\0\5\0G\0Hyper\0\0\0", 16}, {NULL, 0}, {"", 0}], 3) = 16
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\0\311\1\0\0\0\0\210\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 4096, 0, NULL, NULL) = 32
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{";\3\5\0\16\0 \1\0\0\0\0\3\0\3\0\316\2\22\0008\0\5\0\16\0 \1\0000\0\0"..., 16384}, {NULL, 0}, {"", 0}], 3) = 16384
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"6\3\2\0f\0 \1", 8}, {NULL, 0}, {"", 0}], 3) = 8
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=6, events=POLLIN}, {fd=5, events=POLLIN}], 2, 0) = 0 (Timeout)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=6, events=POLLIN}, {fd=5, events=POLLIN}], 2, 0) = 0 (Timeout)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"5\30\4\0\200\0 \1\3\0 \1\316\2\22\0\223\4\5\0\201\0 \1\200\0 \1)\0\0\0"..., 296}, {NULL, 0}, {"", 0}], 3) = 296
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=6, events=POLLIN}, {fd=5, events=POLLIN}], 2, 497) = 0 (Timeout)
poll([{fd=5, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=5, revents=POLLOUT}])
writev(5, [{"(\30\4\0\3\0 \1\1\1\0\0\0\0\0\0", 16}, {NULL, 0}, {"", 0}], 3) = 16
poll([{fd=5, events=POLLIN}], 1, -1)    = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\1\1#\2\0\0\0\0\250\3\300\0o\0N\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 4096, 0, NULL, NULL) = 32
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=6, events=POLLIN}, {fd=5, events=POLLIN}], 2, 4498) = 0 (Timeout)
futex(0x7f2d8af5ea9c, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7f2d8af5ea98, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
recvfrom(5, 0x25ff6c4, 4096, 0, 0, 0)   = -1 EAGAIN (Resource temporarily unavailable)

Answer 1

在....某個部分，套接字被標記為非阻塞，因此獲取EAGAIN （與EWOULDBLOCK ，btw相同的errno(3)值）是完全正常的 - 這意味着在該特定時刻沒有數據要消耗。

然后你的跟蹤確實顯示你每次使用revents=POLLIN進行poll(2)之后都會從套接字獲取數據 ，所以我在這里看不到任何錯誤。 也許只是不成功的讀取總是重復兩次這一事實，但這不是一個真正的問題，只是效率低下（或者反過來說 - 一些非常聰明的技巧）。

Answer 2

您是否在Unix套接字上發送了X11協議請求，您希望收到回復？ 在初始X11協議握手之后，在您請求之前，您將無法從X服務器獲得任何內容 - 通過返回立即響應的請求或注冊您以后的事件的請求。

X11協議非常復雜，試圖編寫自己的代碼來連接它是一個比任何人都要做的要大得多的任務 - 你應該使用libxcb或libX11庫為你處理協議，以及更高級別的工具包，如GTK或Qt來處理大多數小部件和用戶界面。