#ifndef HOST_WIN32
#include <sys/time.h>
#include <sys/types.h>
+#if defined(HAVE_POLL_H)
#include <poll.h>
+#elif defined(HAVE_SYS_POLL_H)
+#include <sys/poll.h>
+#endif
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
-#include <mono/io-layer/atomic.h>
+#include <mono/utils/atomic.h>
#include <mono/metadata/appdomain.h>
#endif
typedef void (*mph_sighandler_t)(int);
typedef struct Mono_Unix_UnixSignal_SignalInfo signal_info;
+#ifndef HOST_WIN32
static int count_handlers (int signum);
+#endif
void*
Mono_Posix_Stdlib_SIG_DFL (void)
#ifndef HOST_WIN32
-#ifdef WAPI_ATOMIC_ASM
+// Atomicity rules: Fields of signal_info read or written by the signal handler
+// (see UnixSignal.cs) should be read and written using atomic functions.
+// (For simplicity, we're protecting some things we don't strictly need to.)
+
+// Because we are in MonoPosixHelper, we are banned from linking mono.
+// We can still use atomic.h because that's all inline functions--
+// unless WAPI_NO_ATOMIC_ASM is defined, in which case atomic.h calls linked functions.
+#ifndef WAPI_NO_ATOMIC_ASM
#define mph_int_get(p) InterlockedExchangeAdd ((p), 0)
#define mph_int_inc(p) InterlockedIncrement ((p))
#define mph_int_dec_test(p) (InterlockedDecrement ((p)) == 0)
- #define mph_int_set(p,o,n) InterlockedExchange ((p), (n))
+ #define mph_int_set(p,n) InterlockedExchange ((p), (n))
+ // Pointer, original, new
+ #define mph_int_test_and_set(p,o,n) (o == InterlockedCompareExchange ((p), (n), (o)))
#elif GLIB_CHECK_VERSION(2,4,0)
#define mph_int_get(p) g_atomic_int_get ((p))
#define mph_int_inc(p) do {g_atomic_int_inc ((p));} while (0)
#define mph_int_dec_test(p) g_atomic_int_dec_and_test ((p))
- #define mph_int_set(p,o,n) do { \
- while (!g_atomic_int_compare_and_exchange ((p), (o), (n))) {} \
- } while (0)
+ #define mph_int_set(p,n) g_atomic_int_set ((p),(n))
+ #define mph_int_test_and_set(p,o,n) g_atomic_int_compare_and_exchange ((p), (o), (n))
#else
- #define mph_int_get(p) (*(p))
- #define mph_int_inc(p) do { (*(p))++; } while (0)
- #define mph_int_dec_test(p) (--(*(p)) == 0)
- #define mph_int_set(p,o,n) do { *(p) = n; } while (0)
+ #error "GLIB 2.4 required because building without ASM atomics"
#endif
#if HAVE_PSIGNAL
return r == -1 && errno == EINTR;
}
+// This tiny ad-hoc read/write lock is needed because of the very specific
+// synchronization needed between default_handler and teardown_pipes:
+// - Many default_handlers can be running at once
+// - The signals_mutex already ensures only one teardown_pipes runs at once
+// - If teardown_pipes starts while a default_handler is ongoing, it must block
+// - If default_handler starts while a teardown_pipes is ongoing, it must *not* block
+// Locks are implemented as ints.
+
+// The lock is split into a teardown bit and a handler count (sign bit unused).
+// There is a teardown running or waiting to run if the teardown bit is set.
+// There is a handler running if the handler count is nonzero.
+#define PIPELOCK_TEARDOWN_BIT ( (int)0x40000000 )
+#define PIPELOCK_COUNT_MASK (~((int)0xC0000000))
+#define PIPELOCK_GET_COUNT(x) ((x) & PIPELOCK_COUNT_MASK)
+#define PIPELOCK_INCR_COUNT(x, by) (((x) & PIPELOCK_TEARDOWN_BIT) | (PIPELOCK_GET_COUNT (PIPELOCK_GET_COUNT (x) + (by))))
+
+static inline void
+acquire_pipelock_teardown (int *lock)
+{
+ int lockvalue_draining;
+ // First mark that a teardown is occurring, so handlers will stop entering the lock.
+ while (1) {
+ int lockvalue = mph_int_get (lock);
+ lockvalue_draining = lockvalue | PIPELOCK_TEARDOWN_BIT;
+ if (mph_int_test_and_set (lock, lockvalue, lockvalue_draining))
+ break;
+ }
+ // Now wait for all handlers to complete.
+ while (1) {
+ if (0 == PIPELOCK_GET_COUNT (lockvalue_draining))
+ break; // We now hold the lock.
+ // Handler is still running, spin until it completes.
+ sched_yield (); // We can call this because !defined(HOST_WIN32)
+ lockvalue_draining = mph_int_get (lock);
+ }
+}
+
+static inline void
+release_pipelock_teardown (int *lock)
+{
+ while (1) {
+ int lockvalue = mph_int_get (lock);
+ int lockvalue_new = lockvalue & ~PIPELOCK_TEARDOWN_BIT;
+ // Technically this can't fail, because we hold both the pipelock and the mutex, but
+ if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
+ return;
+ }
+}
+
+// Return 1 for success
+static inline int
+acquire_pipelock_handler (int *lock)
+{
+ while (1) {
+ int lockvalue = mph_int_get (lock);
+ if (lockvalue & PIPELOCK_TEARDOWN_BIT) // Final lock is being torn down
+ return 0;
+ int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, 1);
+ if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
+ return 1;
+ }
+}
+
+static inline void
+release_pipelock_handler (int *lock)
+{
+ while (1) {
+ int lockvalue = mph_int_get (lock);
+ int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, -1);
+ if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
+ return;
+ }
+}
+
+// This handler is registered once for each UnixSignal object. A pipe is maintained
+// for each one; Wait users read at one end of this pipe, and default_handler sends
+// a write on the pipe for each signal received while the Wait is ongoing.
+//
+// Notice a fairly unlikely race condition exists here: Because we synchronize with
+// pipe teardown, but not install/uninstall (in other words, we are only trying to
+// protect against writing on a closed pipe) it is technically possible a full
+// uninstall and then an install could complete after signum is checked but before
+// the remaining instructions execute. In this unlikely case count could be
+// incremented or a byte written on the wrong signal handler.
static void
default_handler (int signum)
{
signal_info* h = &signals [i];
if (mph_int_get (&h->signum) != signum)
continue;
+
mph_int_inc (&h->count);
+
+ if (!acquire_pipelock_handler (&h->pipelock))
+ continue; // Teardown is occurring on this object, no one to send to.
+
fd = mph_int_get (&h->write_fd);
- if (fd > 0) {
+ if (fd > 0) { // If any listener exists to write to
int j,pipecounter;
- char c = signum;
- pipecounter = mph_int_get (&h->pipecnt);
+ char c = signum; // (Value is meaningless)
+ pipecounter = mph_int_get (&h->pipecnt); // Write one byte per pipe listener
for (j = 0; j < pipecounter; ++j) {
int r;
do { r = write (fd, &c, 1); } while (keep_trying (r));
- fsync (fd); /* force */
}
}
+ release_pipelock_handler (&h->pipelock);
}
}
static pthread_mutex_t signals_mutex = PTHREAD_MUTEX_INITIALIZER;
+// A UnixSignal object is being constructed
void*
Mono_Unix_UnixSignal_install (int sig)
{
+#if defined(HAVE_SIGNAL)
int i;
- signal_info* h = NULL;
- int have_handler = 0;
+ signal_info* h = NULL; // signals[] slot to install to
+ int have_handler = 0; // Candidates for signal_info handler fields
void* handler = NULL;
if (acquire_mutex (&signals_mutex) == -1)
if (sinfo.sa_handler != SIG_DFL || (void*)sinfo.sa_sigaction != (void*)SIG_DFL) {
pthread_mutex_unlock (&signals_mutex);
errno = EADDRINUSE;
- return NULL;
+ return NULL; // This is an rt signal with an existing handler. Bail out.
}
}
#endif /*defined (SIGRTMIN) && defined (SIGRTMAX)*/
+ // Scan through signals list looking for (1) an unused spot (2) a usable value for handler
for (i = 0; i < NUM_SIGNALS; ++i) {
- if (h == NULL && signals [i].signum == 0) {
+ int just_installed = 0;
+ // We're still looking for a signal_info spot, and this one is available:
+ if (h == NULL && mph_int_get (&signals [i].signum) == 0) {
h = &signals [i];
h->handler = signal (sig, default_handler);
if (h->handler == SIG_ERR) {
break;
}
else {
- h->have_handler = 1;
+ just_installed = 1;
}
}
- if (!have_handler && signals [i].signum == sig &&
+ // Check if this slot has a "usable" (not installed by this file) handler-to-restore-later:
+ // (On the first signal to be installed, signals [i] will be == h when this happens.)
+ if (!have_handler && (just_installed || mph_int_get (&signals [i].signum) == sig) &&
signals [i].handler != default_handler) {
have_handler = 1;
handler = signals [i].handler;
}
- if (h && have_handler)
+ if (h && have_handler) // We have everything we need
break;
}
- if (h && have_handler) {
+ if (h) {
+ // If we reached here without have_handler, this means that default_handler
+ // was set as the signal handler before the first UnixSignal object was installed.
+ g_assert (have_handler);
+
+ // Overwrite the tenative handler we set a moment ago with a known-usable one
+ h->handler = handler;
h->have_handler = 1;
- h->handler = handler;
- }
- if (h) {
- mph_int_set (&h->count, h->count, 0);
- mph_int_set (&h->signum, h->signum, sig);
- mph_int_set (&h->pipecnt, h->pipecnt, 0);
+ mph_int_set (&h->count, 0);
+ mph_int_set (&h->pipecnt, 0);
+ mph_int_set (&h->signum, sig);
}
release_mutex (&signals_mutex);
return h;
+#else
+ g_error ("signal() is not supported by this platform");
+ return 0;
+#endif
}
static int
int i;
int count = 0;
for (i = 0; i < NUM_SIGNALS; ++i) {
- if (signals [i].signum == signum)
+ if (mph_int_get (&signals [i].signum) == signum)
++count;
}
return count;
}
+// A UnixSignal object is being Disposed
int
Mono_Unix_UnixSignal_uninstall (void* info)
{
+#if defined(HAVE_SIGNAL)
signal_info* h;
int r = -1;
errno = EINVAL;
else {
/* last UnixSignal -- we can unregister */
- if (h->have_handler && count_handlers (h->signum) == 1) {
- mph_sighandler_t p = signal (h->signum, h->handler);
+ int signum = mph_int_get (&h->signum);
+ if (h->have_handler && count_handlers (signum) == 1) {
+ mph_sighandler_t p = signal (signum, h->handler);
if (p != SIG_ERR)
r = 0;
h->handler = NULL;
h->have_handler = 0;
}
- h->signum = 0;
+ mph_int_set (&h->signum, 0);
}
release_mutex (&signals_mutex);
return r;
+#else
+ g_error ("signal() is not supported by this platform");
+ return 0;
+#endif
}
+// Set up a signal_info to begin waiting for signal
static int
setup_pipes (signal_info** signals, int count, struct pollfd *fd_structs, int *currfd)
{
h = signals [i];
- if (mph_int_get (&h->pipecnt) == 0) {
+ if (mph_int_get (&h->pipecnt) == 0) { // First listener for this signal_info
if ((r = pipe (filedes)) != 0) {
break;
}
- h->read_fd = filedes [0];
- h->write_fd = filedes [1];
+ mph_int_set (&h->read_fd, filedes [0]);
+ mph_int_set (&h->write_fd, filedes [1]);
}
mph_int_inc (&h->pipecnt);
- fd_structs[*currfd].fd = h->read_fd;
+ fd_structs[*currfd].fd = mph_int_get (&h->read_fd);
fd_structs[*currfd].events = POLLIN;
- ++(*currfd);
+ ++(*currfd); // count is verified less than NUM_SIGNALS by caller
}
return r;
}
+// Cleanup a signal_info after waiting for signal
static void
teardown_pipes (signal_info** signals, int count)
{
for (i = 0; i < count; ++i) {
signal_info* h = signals [i];
- if (mph_int_dec_test (&h->pipecnt)) {
- if (h->read_fd != 0)
- close (h->read_fd);
- if (h->write_fd != 0)
- close (h->write_fd);
- h->read_fd = 0;
- h->write_fd = 0;
+ if (mph_int_dec_test (&h->pipecnt)) { // Final listener for this signal_info
+ acquire_pipelock_teardown (&h->pipelock);
+ int read_fd = mph_int_get (&h->read_fd);
+ int write_fd = mph_int_get (&h->write_fd);
+ if (read_fd != 0)
+ close (read_fd);
+ if (write_fd != 0)
+ close (write_fd);
+ mph_int_set (&h->read_fd, 0);
+ mph_int_set (&h->write_fd, 0);
+ release_pipelock_teardown (&h->pipelock);
}
}
}
+// Given pipes set up, wait for a byte to arrive on one of them
static int
wait_for_any (signal_info** signals, int count, int *currfd, struct pollfd* fd_structs, int timeout, Mono_Posix_RuntimeIsShuttingDown shutting_down)
{
int r, idx;
+ // Poll until one of this signal_info's pipes is ready to read.
+ // Once a second, stop to check if the VM is shutting down.
do {
struct timeval tv;
struct timeval *ptv = NULL;
idx = -1;
if (r == 0)
idx = timeout;
- else if (r > 0) {
+ else if (r > 0) { // The pipe[s] are ready to read.
int i;
for (i = 0; i < count; ++i) {
signal_info* h = signals [i];
int r;
char c;
do {
- r = read (h->read_fd, &c, 1);
+ r = read (mph_int_get (&h->read_fd), &c, 1);
} while (keep_trying (r) && !shutting_down ());
if (idx == -1)
idx = i;
projects / mono.git / blobdiff