1 2 /*--------------------------------------------------------------------*/ 3 /*--- Semaphore stuff. sema.c ---*/ 4 /*--------------------------------------------------------------------*/ 5 6 /* 7 This file is part of Valgrind, a dynamic binary instrumentation 8 framework. 9 10 Copyright (C) 2000-2011 Julian Seward 11 jseward (at) acm.org 12 13 This program is free software; you can redistribute it and/or 14 modify it under the terms of the GNU General Public License as 15 published by the Free Software Foundation; either version 2 of the 16 License, or (at your option) any later version. 17 18 This program is distributed in the hope that it will be useful, but 19 WITHOUT ANY WARRANTY; without even the implied warranty of 20 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 21 General Public License for more details. 22 23 You should have received a copy of the GNU General Public License 24 along with this program; if not, write to the Free Software 25 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 26 02111-1307, USA. 27 28 The GNU General Public License is contained in the file COPYING. 29 */ 30 31 #include "pub_core_basics.h" 32 #include "pub_core_debuglog.h" 33 #include "pub_core_vki.h" 34 #include "pub_core_libcassert.h" 35 #include "pub_core_libcfile.h" 36 #include "pub_core_libcproc.h" // For VG_(gettid)() 37 #include "priv_sema.h" 38 39 /* 40 Slower (than the removed futex-based sema scheme) but more portable 41 pipe-based token passing scheme. 42 */ 43 44 /* Cycle the char passed through the pipe through 'A' .. 'Z' to make 45 it easier to make sense of strace/truss output - makes it possible 46 to see more clearly the change of ownership of the lock. Need to 47 be careful to reinitialise it at fork() time. */ 48 static Char sema_char = '!'; /* will cause assertion failures if used 49 before sema_init */ 50 51 void ML_(sema_init)(vg_sema_t *sema) 52 { 53 Char buf[2]; 54 Int res, r; 55 r = VG_(pipe)(sema->pipe); 56 vg_assert(r == 0); 57 58 vg_assert(sema->pipe[0] != sema->pipe[1]); 59 60 sema->pipe[0] = VG_(safe_fd)(sema->pipe[0]); 61 sema->pipe[1] = VG_(safe_fd)(sema->pipe[1]); 62 63 if (0) 64 VG_(debugLog)(0,"zz","sema_init: %d %d\n", sema->pipe[0], 65 sema->pipe[1]); 66 vg_assert(sema->pipe[0] != sema->pipe[1]); 67 68 sema->owner_lwpid = -1; 69 70 /* create initial token */ 71 sema_char = 'A'; 72 buf[0] = sema_char; 73 buf[1] = 0; 74 sema_char++; 75 res = VG_(write)(sema->pipe[1], buf, 1); 76 vg_assert(res == 1); 77 } 78 79 void ML_(sema_deinit)(vg_sema_t *sema) 80 { 81 vg_assert(sema->owner_lwpid != -1); /* must be initialised */ 82 vg_assert(sema->pipe[0] != sema->pipe[1]); 83 VG_(close)(sema->pipe[0]); 84 VG_(close)(sema->pipe[1]); 85 sema->pipe[0] = sema->pipe[1] = -1; 86 sema->owner_lwpid = -1; 87 } 88 89 /* get a token */ 90 void ML_(sema_down)( vg_sema_t *sema, Bool as_LL ) 91 { 92 Char buf[2]; 93 Int ret; 94 Int lwpid = VG_(gettid)(); 95 96 vg_assert(sema->owner_lwpid != lwpid); /* can't have it already */ 97 vg_assert(sema->pipe[0] != sema->pipe[1]); 98 99 again: 100 buf[0] = buf[1] = 0; 101 ret = VG_(read)(sema->pipe[0], buf, 1); 102 103 if (ret != 1) 104 VG_(debugLog)(0, "scheduler", 105 "VG_(sema_down): read returned %d\n", ret); 106 107 if (ret == -VKI_EINTR) 108 goto again; 109 110 vg_assert(ret == 1); /* should get exactly 1 token */ 111 vg_assert(buf[0] >= 'A' && buf[0] <= 'Z'); 112 vg_assert(buf[1] == 0); 113 114 if (sema_char == 'Z') sema_char = 'A'; else sema_char++; 115 116 sema->owner_lwpid = lwpid; 117 sema->held_as_LL = as_LL; 118 } 119 120 /* put token back */ 121 void ML_(sema_up)( vg_sema_t *sema, Bool as_LL ) 122 { 123 Int ret; 124 Char buf[2]; 125 vg_assert(as_LL == sema->held_as_LL); 126 buf[0] = sema_char; 127 buf[1] = 0; 128 vg_assert(sema->owner_lwpid != -1); /* must be initialised */ 129 vg_assert(sema->pipe[0] != sema->pipe[1]); 130 vg_assert(sema->owner_lwpid == VG_(gettid)()); /* must have it */ 131 132 sema->owner_lwpid = 0; 133 134 ret = VG_(write)(sema->pipe[1], buf, 1); 135 136 if (ret != 1) 137 VG_(debugLog)(0, "scheduler", 138 "VG_(sema_up):write returned %d\n", ret); 139 140 vg_assert(ret == 1); 141 } 142 143 /*--------------------------------------------------------------------*/ 144 /*--- end ---*/ 145 /*--------------------------------------------------------------------*/ 146 147 148
