int __system_property_read(const prop_info *pi, char *name, char *value)
{
if (__predict_false(compat_mode)) {
return __system_property_read_compat(pi, name, value);
}
while (true) {
uint32_t serial = __system_property_serial(pi); // acquire semantics
size_t len = SERIAL_VALUE_LEN(serial);
memcpy(value, pi->value, len + 1);
// TODO: Fix the synchronization scheme here.
// There is no fully supported way to implement this kind
// of synchronization in C++11, since the memcpy races with
// updates to pi, and the data being accessed is not atomic.
// The following fence is unintuitive, but would be the
// correct one if memcpy used memory_order_relaxed atomic accesses.
// In practice it seems unlikely that the generated code would
// would be any different, so this should be OK.
atomic_thread_fence(memory_order_acquire);
if (serial ==
load_const_atomic(&(pi->serial), memory_order_relaxed)) {
if (name != 0) {
strcpy(name, pi->name);
}
return len;
}
}
}
void SystemProperties::ReadCallback(const prop_info* pi,
void (*callback)(void* cookie, const char* name,
const char* value, uint32_t serial),
void* cookie) {
// Read only properties don't need to copy the value to a temporary buffer, since it can never
// change.
if (is_read_only(pi->name)) {
uint32_t serial = Serial(pi);
if (pi->is_long()) {
callback(cookie, pi->name, pi->long_value(), serial);
} else {
callback(cookie, pi->name, pi->value, serial);
}
return;
}
while (true) {
uint32_t serial = Serial(pi); // acquire semantics
size_t len = SERIAL_VALUE_LEN(serial);
char value_buf[len + 1];
memcpy(value_buf, pi->value, len);
value_buf[len] = '\0';
// TODO: see todo in Read function
atomic_thread_fence(memory_order_acquire);
if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
callback(cookie, pi->name, value_buf, serial);
return;
}
}
}
/**
* Look up a property by name, copying its value and a
* \0 terminator to the provided pointer. The total bytes
* copied will be no greater than PROP_VALUE_MAX.
*
* \return The string length of the value. A property that
* is not * defined is identical to a property with a
* length 0 value.
*/
int __system_property_read(const prop_info *pi, char *name, char *value)
{
unsigned serial, len;
for(;;) {
serial = pi->serial;
while(SERIAL_DIRTY(serial)) {
struct timespec ts;
ts.tv_sec = 0;
ts.tv_nsec = 100;
futex_wait((volatile void *)&pi->serial, serial, 0);
serial = pi->serial;
}
len = SERIAL_VALUE_LEN(serial);
memcpy(value, pi->value, len + 1);
if(serial == pi->serial) {
if(name != 0) {
strcpy(name, pi->name);
}
return len;
}
}
}
int __system_property_read(const prop_info *pi, char *name, char *value)
{
unsigned serial, len;
if (__predict_false(compat_mode)) {
return __system_property_read_compat(pi, name, value);
}
for(;;) {
serial = pi->serial;
while(SERIAL_DIRTY(serial)) {
__futex_wait((volatile void *)&pi->serial, serial, NULL);
serial = pi->serial;
}
len = SERIAL_VALUE_LEN(serial);
memcpy(value, pi->value, len + 1);
ANDROID_MEMBAR_FULL();
if(serial == pi->serial) {
if(name != 0) {
strcpy(name, pi->name);
}
return len;
}
}
}
void mb__system_property_read_callback(const prop_info* pi,
void (*callback)(void* cookie,
const char* name,
const char* value,
uint32_t serial),
void* cookie) {
#if MB_ENABLE_COMPAT_PROPERTIES
// TODO (dimitry): do we need compat mode for this function?
if (__predict_false(compat_mode)) {
uint32_t serial = mb__system_property_serial_compat(pi);
char name_buf[PROP_NAME_MAX];
char value_buf[PROP_VALUE_MAX];
mb__system_property_read_compat(pi, name_buf, value_buf);
callback(cookie, name_buf, value_buf, serial);
return;
}
#endif
while (true) {
uint32_t serial = mb__system_property_serial(pi); // acquire semantics
size_t len = SERIAL_VALUE_LEN(serial);
char value_buf[len + 1];
memcpy(value_buf, pi->value, len);
value_buf[len] = '\0';
// TODO: see todo in __system_property_read function
atomic_thread_fence(memory_order_acquire);
if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
callback(cookie, pi->name, value_buf, serial);
return;
}
}
}
int mb__system_property_read(const prop_info* pi, char* name, char* value) {
#if MB_ENABLE_COMPAT_PROPERTIES
if (__predict_false(compat_mode)) {
return mb__system_property_read_compat(pi, name, value);
}
#endif
while (true) {
uint32_t serial = mb__system_property_serial(pi); // acquire semantics
size_t len = SERIAL_VALUE_LEN(serial);
memcpy(value, pi->value, len + 1);
// TODO: Fix the synchronization scheme here.
// There is no fully supported way to implement this kind
// of synchronization in C++11, since the memcpy races with
// updates to pi, and the data being accessed is not atomic.
// The following fence is unintuitive, but would be the
// correct one if memcpy used memory_order_relaxed atomic accesses.
// In practice it seems unlikely that the generated code would
// would be any different, so this should be OK.
atomic_thread_fence(memory_order_acquire);
if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
if (name != nullptr) {
size_t namelen = strlcpy(name, pi->name, PROP_NAME_MAX);
if (namelen >= PROP_NAME_MAX) {
LOGE("The property name length for \"%s\" is >= %d;"
" please use __system_property_read_callback"
" to read this property. (the name is truncated to \"%s\")",
pi->name, PROP_NAME_MAX - 1, name);
}
}
return len;
}
}
}
int __system_property_read(const prop_info *pi, char *name, char *value)
{
unsigned serial, len;
for(;;) {
serial = *(unsigned*)((char*)pi + prop_name_max);
while(SERIAL_DIRTY(serial)) {
__futex_wait((volatile void *)((char*)pi + prop_name_max), serial, 0);
serial = *(unsigned*)((char*)pi + prop_name_max);
}
len = SERIAL_VALUE_LEN(serial);
memcpy(value, (char*)pi + prop_name_max + sizeof(pi->serial), len + 1);
if(serial == *(unsigned*)((char*)pi + prop_name_max)) {
if(name != 0) {
strcpy(name, pi->name);
}
return len;
}
}
}
int SystemProperties::Read(const prop_info* pi, char* name, char* value) {
while (true) {
uint32_t serial = Serial(pi); // acquire semantics
size_t len = SERIAL_VALUE_LEN(serial);
memcpy(value, pi->value, len + 1);
// TODO: Fix the synchronization scheme here.
// There is no fully supported way to implement this kind
// of synchronization in C++11, since the memcpy races with
// updates to pi, and the data being accessed is not atomic.
// The following fence is unintuitive, but would be the
// correct one if memcpy used memory_order_relaxed atomic accesses.
// In practice it seems unlikely that the generated code would
// would be any different, so this should be OK.
atomic_thread_fence(memory_order_acquire);
if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
if (name != nullptr) {
size_t namelen = strlcpy(name, pi->name, PROP_NAME_MAX);
if (namelen >= PROP_NAME_MAX) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc",
"The property name length for \"%s\" is >= %d;"
" please use __system_property_read_callback"
" to read this property. (the name is truncated to \"%s\")",
pi->name, PROP_NAME_MAX - 1, name);
}
}
if (is_read_only(pi->name) && pi->is_long()) {
async_safe_format_log(
ANDROID_LOG_ERROR, "libc",
"The property \"%s\" has a value with length %zu that is too large for"
" __system_property_get()/__system_property_read(); use"
" __system_property_read_callback() instead.",
pi->name, strlen(pi->long_value()));
}
return len;
}
}
}