1 // Copyright 2014 The Android Open Source Project 2 // 3 // This software is licensed under the terms of the GNU General Public 4 // License version 2, as published by the Free Software Foundation, and 5 // may be copied, distributed, and modified under those terms. 6 // 7 // This program is distributed in the hope that it will be useful, 8 // but WITHOUT ANY WARRANTY; without even the implied warranty of 9 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 10 // GNU General Public License for more details. 11 12 #ifndef ANDROID_BASE_EINTR_WRAPPER_H 13 #define ANDROID_BASE_EINTR_WRAPPER_H 14 15 #include <errno.h> 16 17 #include "android/base/Log.h" 18 19 namespace android { 20 namespace base { 21 22 // Set EINTR_WRAPPER_DEBUG to 1 to force the debug version of HANDLE_EINTR 23 // which will call eintrWrapperFatal() is the system call loops 24 // too many times, or 0 to get it to loop indefinitly. 25 // Mostly used for unit testing. 26 // If the macro is undefined, auto-detect the value based on NDEBUG. 27 #if !defined(EINTR_WRAPPER_DEBUG) 28 # ifdef NDEBUG 29 # define EINTER_WRAPPER_DEBUG 0 30 # else 31 # define EINTR_WRAPPER_DEBUG 1 32 # endif 33 #endif 34 35 // HANDLE_EINTR() is a macro used to handle EINTR return values when 36 // calling system calls like open() or read() on Posix systems. 37 // 38 // By default, this will loop indefinitly, retrying the call until 39 // the result is no longer -1/EINTR, except in debug mode, where a 40 // loop counter is actually used and to provoke a fatal error if there 41 // are too many loops. 42 // 43 // Usage example: 44 // int ret = HANDLE_EINTR(open("/some/file/path", O_RDONLY)); 45 // 46 // IMPORTANT: Do not use with the close() system call (use IGNORE_EINTR() 47 // instead). 48 // 49 // - On Linux, the file descriptor is always already closed when this 50 // function returns -1/EINTR, and calling it again with the same 51 // parameters risks closing another file descriptor open by another 52 // thread in parallel! 53 // 54 // - On OS X, whether the file descriptor is closed or not is pretty 55 // much random! It's better to leave the descriptor open than risk 56 // closing another one by mistake :( 57 // 58 #ifdef _WIN32 59 # define HANDLE_EINTR(x) (x) 60 #elif EINTR_WRAPPER_DEBUG == 0 61 # define HANDLE_EINTR(x) \ 62 __extension__ ({ \ 63 __typeof__(x) eintr_wrapper_result; \ 64 do { \ 65 eintr_wrapper_result = (x); \ 66 } while (eintr_wrapper_result < 0 && errno == EINTR); \ 67 eintr_wrapper_result; \ 68 }) 69 #else // !_WIN32 && EINTR_WRAPPER_DEBUG 70 71 # define MAX_EINTR_LOOP_COUNT 100 72 73 # define HANDLE_EINTR(x) \ 74 __extension__ ({ \ 75 __typeof__(x) eintr_wrapper_result; \ 76 int eintr_wrapper_loop_count = 0; \ 77 for (;;) { \ 78 eintr_wrapper_result = (x); \ 79 if (eintr_wrapper_result != -1 || errno != EINTR) \ 80 break; \ 81 ++eintr_wrapper_loop_count; \ 82 CHECK(eintr_wrapper_loop_count < MAX_EINTR_LOOP_COUNT) << \ 83 "Looping around EINTR too many times"; \ 84 }; \ 85 eintr_wrapper_result; \ 86 }) 87 #endif // !_WIN32 && EINTR_WRAPPER_DEBUG 88 89 // IGNORE_EINTR() is a macro used to perform a system call and ignore 90 // an EINTR result, i.e. it will return 0 instead of -1 if this occurs. 91 // This is mostly used with the close() system call, as described 92 // in the HANDLE_EINTR() documentation. 93 #ifdef _WIN32 94 # define IGNORE_EINTR(x) (x) 95 #else 96 # define IGNORE_EINTR(x) \ 97 __extension__ ({ \ 98 __typeof__(x) eintr_wrapper_result = (x); \ 99 if (eintr_wrapper_result == -1 && errno == EINTR) \ 100 eintr_wrapper_result = 0; \ 101 eintr_wrapper_result; \ 102 }) 103 #endif 104 105 } // namespace base 106 } // namespace android 107 108 #endif // ANDROID_BASE_EINTR_WRAPPER_H 109
