MEDIUM: fd/threads: Make sure we don't miss a fd cache entry.
An fd cache entry might be removed and added at the end of the list, while
another thread is parsing it, if that happens, we may miss fd cache entries,
to avoid that, add a new field in the struct fdtab, "added_mask", which
contains a mask for potentially affected threads, if it is set, the
corresponding thread will set its bit in fd_cache_mask, to avoid waiting in
poll while it may have more work to do.
diff --git a/include/types/fd.h b/include/types/fd.h
index 8edf26b..0902e7f 100644
--- a/include/types/fd.h
+++ b/include/types/fd.h
@@ -90,14 +90,24 @@
*/
#define DEAD_FD_MAGIC 0xFDDEADFD
+/* fdlist_entry: entry used by the fd cache.
+ * >= 0 means we're in the cache and gives the FD of the next in the cache,
+ * -1 means we're in the cache and the last element,
+ * -2 means the entry is locked,
+ * <= -3 means not in the cache, and next element is -4-fd
+ *
+ * It must remain 8-aligned so that aligned CAS operations may be done on both
+ * entries at once.
+ */
struct fdlist_entry {
- volatile int next;
- volatile int prev;
+ int next;
+ int prev;
} __attribute__ ((aligned(8)));
+/* head of the fd cache */
struct fdlist {
- volatile int first;
- volatile int last;
+ int first;
+ int last;
} __attribute__ ((aligned(8)));
/* info about one given fd */
@@ -106,7 +116,7 @@
unsigned long thread_mask; /* mask of thread IDs authorized to process the task */
unsigned long polled_mask; /* mask of thread IDs currently polling this fd */
unsigned long update_mask; /* mask of thread IDs having an update for fd */
- struct fdlist_entry fdcache_entry; /* Entry in the fdcache */
+ struct fdlist_entry cache; /* Entry in the fdcache */
void (*iocb)(int fd); /* I/O handler */
void *owner; /* the connection or listener associated with this fd, NULL if closed */
unsigned char state; /* FD state for read and write directions (2*3 bits) */