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* Fixed the bug that led to #5119. There was a race condition in the read path

Browse Source 
as soon as a second thread got into the game: if a thread was notified that
  a message is ready, another thread could call read_port() and steal it before
  the previous thread could claim it. The "Extensions" menu still doesn't seem
  to work, but I would guess that is unrelated.
* The threads of the test app never exited, as read_port() returns the number
  of bytes it read, not just a status.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34681 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Axel Dörfler 2009-12-16 12:51:26 +00:00
parent 697255873e
commit 7d592ec4d2
2 changed files with 14 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
src/system/kernel/port.cpp
View File

@ -57,7 +57,7 @@ struct port_entry {
team_id owner;
int32 capacity;
mutex lock;
int32 read_count;
uint32 read_count;
int32 write_count;
ConditionVariable read_condition;
ConditionVariable write_condition;
@ -529,11 +529,7 @@ fill_port_info(struct port_entry* port, port_info* info, size_t size)
info->team = port->owner;
info->capacity = port->capacity;
int32 count = port->read_count;
if (count < 0)
count = 0;
info->queue_count = count;
info->queue_count = port->read_count;
info->total_count = port->total_count;
strlcpy(info->name, port->lock.name, B_OS_NAME_LENGTH);
@ -1057,12 +1053,12 @@ _get_port_message_info_etc(port_id id, port_message_info* info,
if (sPorts[slot].id != id
|| (is_port_closed(slot) && sPorts[slot].messages.IsEmpty())) {
T(Info(sPorts[slot], 0, B_BAD_PORT_ID));
TRACE(("port_buffer_size_etc(): %s port %ld\n",
TRACE(("_get_port_message_info_etc(): %s port %ld\n",
sPorts[slot].id == id ? "closed" : "invalid", id));
return B_BAD_PORT_ID;
}
if (sPorts[slot].read_count <= 0) {
while (sPorts[slot].read_count == 0) {
// We need to wait for a message to appear
if ((flags & B_RELATIVE_TIMEOUT) != 0 && timeout <= 0)
return B_WOULD_BLOCK;
@ -1126,13 +1122,8 @@ port_count(port_id id)
return B_BAD_PORT_ID;
}
int32 count = sPorts[slot].read_count;
// do not return negative numbers
if (count < 0)
count = 0;
// return count of messages
return count;
return sPorts[slot].read_count;
}
@ -1171,12 +1162,10 @@ read_port_etc(port_id id, int32* _code, void* buffer, size_t bufferSize,
return B_BAD_PORT_ID;
}
if (sPorts[slot].read_count <= 0) {
while (sPorts[slot].read_count == 0) {
if ((flags & B_RELATIVE_TIMEOUT) != 0 && timeout <= 0)
return B_WOULD_BLOCK;
sPorts[slot].read_count--;
// We need to wait for a message to appear
ConditionVariableEntry entry;
sPorts[slot].read_condition.Add(&entry);
@ -1200,8 +1189,7 @@ read_port_etc(port_id id, int32* _code, void* buffer, size_t bufferSize,
sPorts[slot].read_count++;
return status != B_OK ? status : entry.WaitStatus();
}
} else
sPorts[slot].read_count--;
}
// determine tail & get the length of the message
port_message* message = sPorts[slot].messages.Head();
@ -1216,7 +1204,6 @@ read_port_etc(port_id id, int32* _code, void* buffer, size_t bufferSize,
T(Read(sPorts[slot], message->code, size));
sPorts[slot].read_count++;
sPorts[slot].read_condition.NotifyOne();
// we only peeked, but didn't grab the message
return size;
@ -1225,6 +1212,7 @@ read_port_etc(port_id id, int32* _code, void* buffer, size_t bufferSize,
sPorts[slot].messages.RemoveHead();
sPorts[slot].total_count++;
sPorts[slot].write_count++;
sPorts[slot].read_count--;
notify_port_select_events(slot, B_EVENT_WRITE);
sPorts[slot].write_condition.NotifyOne();

13
src/tests/system/kernel/port_multi_read_test.cpp
View File

@ -21,16 +21,15 @@ read_thread(void* _data)
printf("[%ld] read port...\n", find_thread(NULL));
while (true) {
ssize_t bytesWaiting = port_buffer_size(port);
printf("[%ld] buffer size %ld waiting\n", find_thread(NULL),
bytesWaiting);
ssize_t bytes = port_buffer_size(port);
printf("[%ld] buffer size %ld waiting\n", find_thread(NULL), bytes);
char buffer[256];
int32 code;
status_t status = read_port(port, &code, buffer, sizeof(buffer));
bytes = read_port(port, &code, buffer, sizeof(buffer));
printf("[%ld] read port result (code %lx): %s\n", find_thread(NULL),
code, strerror(status));
if (status == B_OK)
code, strerror(bytes));
if (bytes >= 0)
break;
}
@ -51,7 +50,7 @@ main()
resume_thread(threads[i]);
}
printf("snooze for a bit, all threads should be waiting now.");
printf("snooze for a bit, all threads should be waiting now.\n");
snooze(100000);
for (int32 i = 0; i < THREAD_COUNT; i++) {