support/signal.c

   1 /*
   2  * <signal.h> wrapper functions.
   3  *
   4  * Authors:
   5  *   Jonathan Pryor (jonpryor@vt.edu)
   6  *   Jonathan Pryor (jpryor@novell.com)
   7  *   Tim Jenks (tim.jenks@realtimeworlds.com)
   8  *
   9  * Copyright (C) 2004-2005 Jonathan Pryor
  10  * Copyright (C) 2008 Novell, Inc.
  11  */
  12
  13 #include <signal.h>
  14
  15 #include "map.h"
  16 #include "mph.h"
  17
  18 #ifndef HOST_WIN32
  19 #include <sys/time.h>
  20 #include <sys/types.h>
  21 #if defined(HAVE_POLL_H)
  22 #include <poll.h>
  23 #elif defined(HAVE_SYS_POLL_H)
  24 #include <sys/poll.h>
  25 #endif
  26 #include <unistd.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <pthread.h>
  30 #include <mono/utils/atomic.h>
  31 #include <mono/metadata/appdomain.h>
  32 #endif
  33
  34 G_BEGIN_DECLS
  35
  36 typedef void (*mph_sighandler_t)(int);
  37 typedef struct Mono_Unix_UnixSignal_SignalInfo signal_info;
  38
  39 #ifndef HOST_WIN32
  40 static int count_handlers (int signum);
  41 #endif
  42
  43 void*
  44 Mono_Posix_Stdlib_SIG_DFL (void)
  45 {
  46         return SIG_DFL;
  47 }
  48
  49 void*
  50 Mono_Posix_Stdlib_SIG_ERR (void)
  51 {
  52         return SIG_ERR;
  53 }
  54
  55 void*
  56 Mono_Posix_Stdlib_SIG_IGN (void)
  57 {
  58         return SIG_IGN;
  59 }
  60
  61 void
  62 Mono_Posix_Stdlib_InvokeSignalHandler (int signum, void *handler)
  63 {
  64         mph_sighandler_t _h = (mph_sighandler_t) handler;
  65         _h (signum);
  66 }
  67
  68 int Mono_Posix_SIGRTMIN (void)
  69 {
  70 #ifdef SIGRTMIN
  71         return SIGRTMIN;
  72 #else /* def SIGRTMIN */
  73         return -1;
  74 #endif /* ndef SIGRTMIN */
  75 }
  76
  77 int Mono_Posix_SIGRTMAX (void)
  78 {
  79 #ifdef SIGRTMAX
  80         return SIGRTMAX;
  81 #else /* def SIGRTMAX */
  82         return -1;
  83 #endif /* ndef SIGRTMAX */
  84 }
  85
  86 int Mono_Posix_FromRealTimeSignum (int offset, int *r)
  87 {
  88         if (NULL == r) {
  89                 errno = EINVAL;
  90                 return -1;
  91         }
  92         *r = 0;
  93 #if defined (SIGRTMIN) && defined (SIGRTMAX)
  94         if ((offset < 0) || (SIGRTMIN > SIGRTMAX - offset)) {
  95                 errno = EINVAL;
  96                 return -1;
  97         }
  98         *r = SIGRTMIN+offset;
  99         return 0;
 100 #else /* defined (SIGRTMIN) && defined (SIGRTMAX) */
 101 # ifdef ENOSYS
 102         errno = ENOSYS;
 103 # endif /* ENOSYS */
 104         return -1;
 105 #endif /* defined (SIGRTMIN) && defined (SIGRTMAX) */
 106 }
 107
 108 #ifndef HOST_WIN32
 109
 110 // Atomicity rules: Fields of signal_info read or written by the signal handler
 111 // (see UnixSignal.cs) should be read and written using atomic functions.
 112 // (For simplicity, we're protecting some things we don't strictly need to.)
 113
 114 // Because we are in MonoPosixHelper, we are banned from linking mono.
 115 // We can still use atomic.h because that's all inline functions--
 116 // unless WAPI_NO_ATOMIC_ASM is defined, in which case atomic.h calls linked functions.
 117 #ifndef WAPI_NO_ATOMIC_ASM
 118         #define mph_int_get(p)     InterlockedExchangeAdd ((p), 0)
 119         #define mph_int_inc(p)     InterlockedIncrement ((p))
 120         #define mph_int_dec_test(p)     (InterlockedDecrement ((p)) == 0)
 121         #define mph_int_set(p,n) InterlockedExchange ((p), (n))
 122         // Pointer, original, new
 123         #define mph_int_test_and_set(p,o,n) (o == InterlockedCompareExchange ((p), (n), (o)))
 124 #elif GLIB_CHECK_VERSION(2,4,0)
 125         #define mph_int_get(p) g_atomic_int_get ((p))
 126         #define mph_int_inc(p) do {g_atomic_int_inc ((p));} while (0)
 127         #define mph_int_dec_test(p) g_atomic_int_dec_and_test ((p))
 128         #define mph_int_set(p,n) g_atomic_int_set ((p),(n))
 129         #define mph_int_test_and_set(p,o,n) g_atomic_int_compare_and_exchange ((p), (o), (n))
 130 #else
 131         #error "GLIB 2.4 required because building without ASM atomics"
 132 #endif
 133
 134 #if HAVE_PSIGNAL
 135 int
 136 Mono_Posix_Syscall_psignal (int sig, const char* s)
 137 {
 138         errno = 0;
 139         psignal (sig, s);
 140         return errno == 0 ? 0 : -1;
 141 }
 142 #endif  /* def HAVE_PSIGNAL */
 143
 144 #define NUM_SIGNALS 64
 145 static signal_info signals[NUM_SIGNALS];
 146
 147 static int acquire_mutex (pthread_mutex_t *mutex)
 148 {
 149         int mr;
 150         while ((mr = pthread_mutex_lock (mutex)) == EAGAIN) {
 151                 /* try to acquire again */
 152         }
 153         if ((mr != 0) && (mr != EDEADLK))  {
 154                 errno = mr;
 155                 return -1;
 156         }
 157         return 0;
 158 }
 159
 160 static void release_mutex (pthread_mutex_t *mutex)
 161 {
 162         int mr;
 163         while ((mr = pthread_mutex_unlock (mutex)) == EAGAIN) {
 164                 /* try to release mutex again */
 165         }
 166 }
 167
 168 static inline int
 169 keep_trying (int r)
 170 {
 171         return r == -1 && errno == EINTR;
 172 }
 173
 174 // This tiny ad-hoc read/write lock is needed because of the very specific
 175 // synchronization needed between default_handler and teardown_pipes:
 176 // - Many default_handlers can be running at once
 177 // - The signals_mutex already ensures only one teardown_pipes runs at once
 178 // - If teardown_pipes starts while a default_handler is ongoing, it must block
 179 // - If default_handler starts while a teardown_pipes is ongoing, it must *not* block
 180 // Locks are implemented as ints.
 181
 182 // The lock is split into a teardown bit and a handler count (sign bit unused).
 183 // There is a teardown running or waiting to run if the teardown bit is set.
 184 // There is a handler running if the handler count is nonzero.
 185 #define PIPELOCK_TEARDOWN_BIT (  (int)0x40000000 )
 186 #define PIPELOCK_COUNT_MASK   (~((int)0xC0000000))
 187 #define PIPELOCK_GET_COUNT(x)      ((x) & PIPELOCK_COUNT_MASK)
 188 #define PIPELOCK_INCR_COUNT(x, by) (((x) & PIPELOCK_TEARDOWN_BIT) | (PIPELOCK_GET_COUNT (PIPELOCK_GET_COUNT (x) + (by))))
 189
 190 static inline void
 191 acquire_pipelock_teardown (int *lock)
 192 {
 193         int lockvalue_draining;
 194         // First mark that a teardown is occurring, so handlers will stop entering the lock.
 195         while (1) {
 196                 int lockvalue = mph_int_get (lock);
 197                 lockvalue_draining = lockvalue | PIPELOCK_TEARDOWN_BIT;
 198                 if (mph_int_test_and_set (lock, lockvalue, lockvalue_draining))
 199                         break;
 200         }
 201         // Now wait for all handlers to complete.
 202         while (1) {
 203                 if (0 == PIPELOCK_GET_COUNT (lockvalue_draining))
 204                         break; // We now hold the lock.
 205                 // Handler is still running, spin until it completes.
 206                 sched_yield (); // We can call this because !defined(HOST_WIN32)
 207                 lockvalue_draining = mph_int_get (lock);
 208         }
 209 }
 210
 211 static inline void
 212 release_pipelock_teardown (int *lock)
 213 {
 214         while (1) {
 215                 int lockvalue = mph_int_get (lock);
 216                 int lockvalue_new = lockvalue & ~PIPELOCK_TEARDOWN_BIT;
 217                 // Technically this can't fail, because we hold both the pipelock and the mutex, but
 218                 if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
 219                         return;
 220         }
 221 }
 222
 223 // Return 1 for success
 224 static inline int
 225 acquire_pipelock_handler (int *lock)
 226 {
 227         while (1) {
 228                 int lockvalue = mph_int_get (lock);
 229                 if (lockvalue & PIPELOCK_TEARDOWN_BIT) // Final lock is being torn down
 230                         return 0;
 231                 int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, 1);
 232                 if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
 233                         return 1;
 234         }
 235 }
 236
 237 static inline void
 238 release_pipelock_handler (int *lock)
 239 {
 240         while (1) {
 241                 int lockvalue = mph_int_get (lock);
 242                 int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, -1);
 243                 if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
 244                         return;
 245         }
 246 }
 247
 248 // This handler is registered once for each UnixSignal object. A pipe is maintained
 249 // for each one; Wait users read at one end of this pipe, and default_handler sends
 250 // a write on the pipe for each signal received while the Wait is ongoing.
 251 //
 252 // Notice a fairly unlikely race condition exists here: Because we synchronize with
 253 // pipe teardown, but not install/uninstall (in other words, we are only trying to
 254 // protect against writing on a closed pipe) it is technically possible a full
 255 // uninstall and then an install could complete after signum is checked but before
 256 // the remaining instructions execute. In this unlikely case count could be
 257 // incremented or a byte written on the wrong signal handler.
 258 static void
 259 default_handler (int signum)
 260 {
 261         int i;
 262         for (i = 0; i < NUM_SIGNALS; ++i) {
 263                 int fd;
 264                 signal_info* h = &signals [i];
 265                 if (mph_int_get (&h->signum) != signum)
 266                         continue;
 267
 268                 mph_int_inc (&h->count);
 269
 270                 if (!acquire_pipelock_handler (&h->pipelock))
 271                         continue; // Teardown is occurring on this object, no one to send to.
 272
 273                 fd = mph_int_get (&h->write_fd);
 274                 if (fd > 0) { // If any listener exists to write to
 275                         int j,pipecounter;
 276                         char c = signum; // (Value is meaningless)
 277                         pipecounter = mph_int_get (&h->pipecnt); // Write one byte per pipe listener
 278                         for (j = 0; j < pipecounter; ++j) {
 279                                 int r;
 280                                 do { r = write (fd, &c, 1); } while (keep_trying (r));
 281                         }
 282                 }
 283                 release_pipelock_handler (&h->pipelock);
 284         }
 285 }
 286
 287 static pthread_mutex_t signals_mutex = PTHREAD_MUTEX_INITIALIZER;
 288
 289 // A UnixSignal object is being constructed
 290 void*
 291 Mono_Unix_UnixSignal_install (int sig)
 292 {
 293 #if defined(HAVE_SIGNAL)
 294         int i;
 295         signal_info* h = NULL;        // signals[] slot to install to
 296         int have_handler = 0;         // Candidates for signal_info handler fields
 297         void* handler = NULL;
 298
 299         if (acquire_mutex (&signals_mutex) == -1)
 300                 return NULL;
 301
 302 #if defined (SIGRTMIN) && defined (SIGRTMAX)
 303         /*The runtime uses some rt signals for itself so it's important to not override them.*/
 304         if (sig >= SIGRTMIN && sig <= SIGRTMAX && count_handlers (sig) == 0) {
 305                 struct sigaction sinfo;
 306                 sigaction (sig, NULL, &sinfo);
 307                 if (sinfo.sa_handler != SIG_DFL || (void*)sinfo.sa_sigaction != (void*)SIG_DFL) {
 308                         pthread_mutex_unlock (&signals_mutex);
 309                         errno = EADDRINUSE;
 310                         return NULL; // This is an rt signal with an existing handler. Bail out.
 311                 }
 312         }
 313 #endif /*defined (SIGRTMIN) && defined (SIGRTMAX)*/
 314
 315         // Scan through signals list looking for (1) an unused spot (2) a usable value for handler
 316         for (i = 0; i < NUM_SIGNALS; ++i) {
 317                 int just_installed = 0;
 318                 // We're still looking for a signal_info spot, and this one is available:
 319                 if (h == NULL && mph_int_get (&signals [i].signum) == 0) {
 320                         h = &signals [i];
 321                         h->handler = signal (sig, default_handler);
 322                         if (h->handler == SIG_ERR) {
 323                                 h->handler = NULL;
 324                                 h = NULL;
 325                                 break;
 326                         }
 327                         else {
 328                                 just_installed = 1;
 329                         }
 330                 }
 331                 // Check if this slot has a "usable" (not installed by this file) handler-to-restore-later:
 332                 // (On the first signal to be installed, signals [i] will be == h when this happens.)
 333                 if (!have_handler && (just_installed || mph_int_get (&signals [i].signum) == sig) &&
 334                                 signals [i].handler != default_handler) {
 335                         have_handler = 1;
 336                         handler = signals [i].handler;
 337                 }
 338                 if (h && have_handler) // We have everything we need
 339                         break;
 340         }
 341
 342         if (h) {
 343                 // If we reached here without have_handler, this means that default_handler
 344                 // was set as the signal handler before the first UnixSignal object was installed.
 345                 g_assert (have_handler);
 346
 347                 // Overwrite the tenative handler we set a moment ago with a known-usable one
 348                 h->handler = handler;
 349                 h->have_handler = 1;
 350
 351                 mph_int_set (&h->count, 0);
 352                 mph_int_set (&h->pipecnt, 0);
 353                 mph_int_set (&h->signum, sig);
 354         }
 355
 356         release_mutex (&signals_mutex);
 357
 358         return h;
 359 #else
 360         g_error ("signal() is not supported by this platform");
 361         return 0;
 362 #endif
 363 }
 364
 365 static int
 366 count_handlers (int signum)
 367 {
 368         int i;
 369         int count = 0;
 370         for (i = 0; i < NUM_SIGNALS; ++i) {
 371                 if (mph_int_get (&signals [i].signum) == signum)
 372                         ++count;
 373         }
 374         return count;
 375 }
 376
 377 // A UnixSignal object is being Disposed
 378 int
 379 Mono_Unix_UnixSignal_uninstall (void* info)
 380 {
 381 #if defined(HAVE_SIGNAL)
 382         signal_info* h;
 383         int r = -1;
 384
 385         if (acquire_mutex (&signals_mutex) == -1)
 386                 return -1;
 387
 388         h = info;
 389
 390         if (h == NULL || h < signals || h > &signals [NUM_SIGNALS])
 391                 errno = EINVAL;
 392         else {
 393                 /* last UnixSignal -- we can unregister */
 394                 int signum = mph_int_get (&h->signum);
 395                 if (h->have_handler && count_handlers (signum) == 1) {
 396                         mph_sighandler_t p = signal (signum, h->handler);
 397                         if (p != SIG_ERR)
 398                                 r = 0;
 399                         h->handler      = NULL;
 400                         h->have_handler = 0;
 401                 }
 402                 mph_int_set (&h->signum, 0);
 403         }
 404
 405         release_mutex (&signals_mutex);
 406
 407         return r;
 408 #else
 409         g_error ("signal() is not supported by this platform");
 410         return 0;
 411 #endif
 412 }
 413
 414 // Set up a signal_info to begin waiting for signal
 415 static int
 416 setup_pipes (signal_info** signals, int count, struct pollfd *fd_structs, int *currfd)
 417 {
 418         int i;
 419         int r = 0;
 420         for (i = 0; i < count; ++i) {
 421                 signal_info* h;
 422                 int filedes[2];
 423
 424                 h = signals [i];
 425
 426                 if (mph_int_get (&h->pipecnt) == 0) { // First listener for this signal_info
 427                         if ((r = pipe (filedes)) != 0) {
 428                                 break;
 429                         }
 430                         mph_int_set (&h->read_fd,  filedes [0]);
 431                         mph_int_set (&h->write_fd, filedes [1]);
 432                 }
 433                 mph_int_inc (&h->pipecnt);
 434                 fd_structs[*currfd].fd = mph_int_get (&h->read_fd);
 435                 fd_structs[*currfd].events = POLLIN;
 436                 ++(*currfd); // count is verified less than NUM_SIGNALS by caller
 437         }
 438         return r;
 439 }
 440
 441 // Cleanup a signal_info after waiting for signal
 442 static void
 443 teardown_pipes (signal_info** signals, int count)
 444 {
 445         int i;
 446         for (i = 0; i < count; ++i) {
 447                 signal_info* h = signals [i];
 448
 449                 if (mph_int_dec_test (&h->pipecnt)) { // Final listener for this signal_info
 450                         acquire_pipelock_teardown (&h->pipelock);
 451                         int read_fd = mph_int_get (&h->read_fd);
 452                         int write_fd = mph_int_get (&h->write_fd);
 453                         if (read_fd != 0)
 454                                 close (read_fd);
 455                         if (write_fd != 0)
 456                                 close (write_fd);
 457                         mph_int_set (&h->read_fd, 0);
 458                         mph_int_set (&h->write_fd, 0);
 459                         release_pipelock_teardown (&h->pipelock);
 460                 }
 461         }
 462 }
 463
 464 // Given pipes set up, wait for a byte to arrive on one of them
 465 static int
 466 wait_for_any (signal_info** signals, int count, int *currfd, struct pollfd* fd_structs, int timeout, Mono_Posix_RuntimeIsShuttingDown shutting_down)
 467 {
 468         int r, idx;
 469         // Poll until one of this signal_info's pipes is ready to read.
 470         // Once a second, stop to check if the VM is shutting down.
 471         do {
 472                 struct timeval tv;
 473                 struct timeval *ptv = NULL;
 474                 if (timeout != -1) {
 475                         tv.tv_sec  = timeout / 1000;
 476                         tv.tv_usec = (timeout % 1000)*1000;
 477                         ptv = &tv;
 478                 }
 479                 r = poll (fd_structs, count, timeout);
 480         } while (keep_trying (r) && !shutting_down ());
 481
 482         idx = -1;
 483         if (r == 0)
 484                 idx = timeout;
 485         else if (r > 0) { // The pipe[s] are ready to read.
 486                 int i;
 487                 for (i = 0; i < count; ++i) {
 488                         signal_info* h = signals [i];
 489                         if (fd_structs[i].revents & POLLIN) {
 490                                 int r;
 491                                 char c;
 492                                 do {
 493                                         r = read (mph_int_get (&h->read_fd), &c, 1);
 494                                 } while (keep_trying (r) && !shutting_down ());
 495                                 if (idx == -1)
 496                                         idx = i;
 497                         }
 498                 }
 499         }
 500
 501         return idx;
 502 }
 503
 504 /*
 505  * returns: -1 on error:
 506  *          timeout on timeout
 507  *          index into _signals array of signal that was generated on success
 508  */
 509 int
 510 Mono_Unix_UnixSignal_WaitAny (void** _signals, int count, int timeout /* milliseconds */, Mono_Posix_RuntimeIsShuttingDown shutting_down)
 511 {
 512         int r;
 513         int currfd = 0;
 514         struct pollfd fd_structs[NUM_SIGNALS];
 515
 516         signal_info** signals = (signal_info**) _signals;
 517
 518         if (count > NUM_SIGNALS)
 519                 return -1;
 520
 521         if (acquire_mutex (&signals_mutex) == -1)
 522                 return -1;
 523
 524         r = setup_pipes (signals, count, &fd_structs[0], &currfd);
 525
 526         release_mutex (&signals_mutex);
 527
 528         if (r == 0) {
 529                 r = wait_for_any (signals, count, &currfd, &fd_structs[0], timeout, shutting_down);
 530         }
 531
 532         if (acquire_mutex (&signals_mutex) == -1)
 533                 return -1;
 534
 535         teardown_pipes (signals, count);
 536
 537         release_mutex (&signals_mutex);
 538
 539         return r;
 540 }
 541
 542 #endif /* ndef HOST_WIN32 */
 543
 544
 545 G_END_DECLS
 546
 547 /*
 548  * vim: noexpandtab
 549  */