+/* Request, response and cache data structures:
+ *
+ * cache[] (defined later):
+ * cacheline_t cache[cache_size] array, or in other words,
+ * user_req* cache[cache_size][8] array.
+ * Every client request is hashed, hash value determines which cache[x]
+ * will have the response stored in one of its 8 elements.
+ * Cache entries have this format: request, then padding to 32 bits,
+ * then the response.
+ * Addresses in cache[x][y] may be NULL or:
+ * (&client_buf[z]) & 1: the cache miss is in progress ("future entry"):
+ * "the data is not in the cache (yet), wait for it to appear"
+ * (&client_buf[z]) & 3: the cache miss is in progress and other clients
+ * also want the same data ("shared future entry")
+ * else (non-NULL but low two bits are 0): cached data in malloc'ed block
+ *
+ * Each of these is a [max_reqnum] sized array:
+ * pfd[i] - given to poll() to wait for requests and replies.
+ * .fd: first two pfd[i]: listening Unix domain sockets, else
+ * .fd: open fd to a client, for reading client's request, or
+ * .fd: open fd to a worker, to send request and get response back
+ * cinfo[i] - auxiliary client data for pfd[i]
+ * .client_fd: open fd to a client, in case we already had read its
+ * request and got a cache miss, and created a worker or
+ * wait for another client's worker.
+ * Otherwise, it's 0 and client's fd is in pfd[i].fd
+ * .bufidx: index in client_buf[] we store client's request in
+ * .bytecnt: size of the request
+ * .started_ms: used to time out unresponsive clients
+ * .respos:
+ * .resptr:
+ * .cache_pp: &cache[x][y] where the response is, or will be stored.
+ * .ureq:
+ * When a client has received its reply (or otherwise closed (timeout etc)),
+ * corresponding pfd[i] and cinfo[i] are removed by shifting [i+1], [i+2] etc
+ * elements down, so that both arrays never have free holes.
+ * [num_clients] is always the first free element.
+ *
+ * Each of these also is a [max_reqnum] sized array, but indexes
+ * do not correspond directly to pfd[i] and cinfo[i]:
+ * client_buf[n][MAX_USER_REQ_SIZE] - buffers we read client requests into
+ * busy_cbuf[n] - bool flags marking busy client_buf[]
+ */
+/* Possible reductions:
+ * fd, bufidx - uint8_t
+ * started_ms -> uint16_t started_s
+ * ureq - eliminate (derivable from bufidx?)
+ */
+
+/* Are special bits 0? is it a true cached entry? */
+#define CACHED_ENTRY(p) ( ((long)(p) & 3) == 0 )
+/* Are special bits 11? is it a shared future cache entry? */
+#define CACHE_SHARED(p) ( ((long)(p) & 3) == 3 )
+/* Return a ptr with special bits cleared (used for accessing data) */
+#define CACHE_PTR(p) ( (void*) ((long)(p) & ~(long)3) )
+/* Return a ptr with special bits set to x1: make future cache entry ptr */
+#define MAKE_FUTURE_PTR(p) ( (void*) ((long)(p) | 1) )
+/* Modify ptr, set special bits to 11: shared future cache entry */
+#define MARK_PTR_SHARED(pp) ( *(long*)(pp) |= 3 )
+
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