Lievent Source Analysis: Evbuffer

The struct evbuffer is defined in the Evbuffer-internal.h file.

The Evbuffer structure holds a linked list with evbuffer-chain structure as a node, and there are two pointers within the evbuffer that point to the end and end nodes respectively.

1 structEvbuffer {2     /** The first chain in this buffer ' s linked list of chains.*/3     structEvbuffer_chain *First ;4     /** The last chain in this buffer ' s linked list of chains.*/5     structEvbuffer_chain *Last ;6 7     /** Pointer to the next Pointer pointing at the ' Last_with_data ' chain.8      *9 * to unpack:Ten      * One * The Last_with_data chain is the last chain of that have any data in it. A * If All chains in the buffer was empty, it is the first chain. - * If The buffer has no chains, it is NULL. -      * the * The Last_with_datap pointer points at _whatever ' Next ' pointer_ - * points at the Last_with_datap chain. If the Last_with_data chain - * is the first chain, or it was NULL, then the Last_with_datap pointer - * is &buf->first. +      */ -     structEvbuffer_chain * *Last_with_datap; +  A     /** Total amount of bytes stored in all chains.*/ at size_t Total_len; -  -     /** Number of bytes We have added to the buffer since we last tried to - * Invoke callbacks.*/ - size_t N_ADD_FOR_CB; -     /** Number of bytes we have removed from the buffer since we last in * tried to invoke callbacks.*/ - size_t N_DEL_FOR_CB; to  + #ifndef Event__disable_thread_support -     /** A lock used to mediate access to this buffer.*/ the     void*Lock; * #endif $     /** True iff we should free the lock field if we free thisPanax Notoginseng * Evbuffer.*/ -Unsigned own_lock:1; the     /** True iff we should not allow changes to the front of the buffer + * (drains or prepends).*/ AUnsigned freeze_start:1; the     /** True iff we should not allow changes to the end of the buffer + * (appends)*/ -Unsigned freeze_end:1; $     /** True iff this evbuffer ' s callbacks is not invoked immediately $ * Upon a change in the buffer, but instead is deferred to be invoked - * from the Event_base ' s loop. Useful for preventing enormous stack - * Overflows when we had mutually recursive callbacks, and for the * Serializing callbacks in a single thread.*/ -Unsigned Deferred_cbs:1;Wuyi #ifdef _WIN32 the     /** True iff this buffer is set to overlapped IO.*/ -Unsigned is_overlapped:1; Wu #endif -     /** Zero or more evbuffer_flag_* bits*/ About ev_uint32_t flags; $  -     /** Used to implement deferred callbacks.*/ -     structEvent_base *Cb_queue; -  A     /** A reference count on this evbuffer. When the reference count + * reaches 0, the buffer is destroyed. Manipulated with the * Evbuffer_incref and Evbuffer_decref_and_unlock and - * Evbuffer_free.*/ $     intrefcnt; the  the     /** A struct event_callback handle to make all of the this buffer ' s callbacks the * Invoked from the event loop.*/ the     structEvent_callback deferred; -  in     /** A Doubly-linked-list of callback functions*/ the List_head (Evbuffer_cb_queue, Evbuffer_cb_entry) callbacks; the  About     /** The parent Bufferevent object this evbuffer belongs to. the * NULL If the evbuffer stands alone.*/ the     structBufferevent *parent; the};

struct Evbuffer_chain:

Inside the evbuffer-chain structure, a variable that represents the length of the buffer content and a pointer to a char* point to the location of the buffer content.

1 /** A Single item in an Evbuffer.*/2 structEvbuffer_chain {3     /** points to next buffer in the chain*/4     structEvbuffer_chain *Next;5 6     /** Total allocation available in the buffer field.*/7 size_t Buffer_len;8 9     /** Unused space at the beginning of buffer or an offset into aTen * file for sendfile buffers.*/ One ev_misalign_t misalign; A  -     /** Offset into buffer + misalign at which to start writing. - * In other words, the total number of bytes actually stored the * in buffer.*/ - size_t off; -  -     /** Set If special handling is required for this chain*/ + unsigned flags; - #defineEvbuffer_filesegment 0x0001/**< A chain used for A file segment */ + #defineEvbuffer_sendfile 0x0002/**< A chain used with SENDFILE */ A #defineEvbuffer_reference 0x0004/**< A chain with a mem REFERENCE */ at #defineEvbuffer_immutable 0x0008/**< read-only Chain * * -     /** A chain that mustn ' t is reallocated or freed, or has its contents - * memmoved, until the chain is un-pinned.*/ - #defineEvbuffer_mem_pinned_r 0x0010 - #defineEvbuffer_mem_pinned_w 0x0020 - #defineEvbuffer_mem_pinned_any (evbuffer_mem_pinned_r| EVBUFFER_MEM_PINNED_W) in     /** A chain that should being freed, but can ' t be freed until it 's - * un-pinned.*/ to #defineEvbuffer_dangling 0x0040 +     /** A chain that is a referenced copy of another chain*/ - #defineEvbuffer_multicast 0x0080 the  *     /** Number of references to this chain*/ $     intrefcnt;Panax Notoginseng  -     /** Usually points to the read-write memory belonging to this the * Buffer Allocated as part of the Evbuffer_chain allocation. + * For Mmap, the can be a read-only buffer and A * Evbuffer_immutable'll is set in flags. For Sendfile, it the * May point to NULL. +      */ -UnsignedChar*buffer; $ }; $  - /** Callback for a reference chain, lets us know what-if - * we ' re do with it. Lives at the end of a evbuffer_chain with the the * Evbuffer_reference flag set*/ - structEvbuffer_chain_reference {Wuyi EVBUFFER_REF_CLEANUP_CB CLEANUPFN; the     void*Extra; -};

Lievent Source Analysis: Evbuffer