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118 lines
6.2 KiB
118 lines
6.2 KiB
5 years ago
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//========= Copyright Valve Corporation, All rights reserved. ============//
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//
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// download_internal.h
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//
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// Header file for optional HTTP asset downloading
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// Author: Matthew D. Campbell (matt@turtlerockstudios.com), 2004
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//
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//=======================================================================================//
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#ifndef DOWNLOAD_INTERNAL_H
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#define DOWNLOAD_INTERNAL_H
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/**
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* -------------------
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* Download overview:
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* HTTP downloading is done outside the main thread, to increase responsiveness
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* and for code clarity (the download can be a linear sequence of blocking calls).
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*
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* The process is as follows, from the perspective of the main thread:
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* 1. Downloads are queued up when connecting to a server, if the server sends
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* a download URL.
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* 2. If HTTP downloads are queued up, the client disconnects from the server,
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* and puts up a progress bar dialog box for the transfers.
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* 3. The CL_HTTPUpdate() function is called every frame, and it does the following:
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* a) Starts a download thread if none are active, and at least one is queued up.
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* b) Checks on status of the current transfer and updates the progress bar.
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* i. If the thread has finished, the file is written out to disk and another
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* transfer is started.
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* ii. If the thread has aborted/errored out, any partial data is written to
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* the cache, the progress bar is removed, and an error message is
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* shown, if neccessary.
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* c) Checks for old transfers to clean up where the download thread has exited.
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* 4. If the user hits Cancel on the progress bar, the current download is told to
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* abort, and the progress bar is removed.
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*
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* The process is as follows, from the perspective of the download thread:
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* 1. A complete URL is constructed and verified for correctness.
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* 2. The connection is established with the server.
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* 3. The file is requested from the server, including the file timestamp and
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* byte range for partial transfers (resuming an aborted transfer). A buffer
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* for the data is allocated in this thread.
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* 4. while the main thread has not requested an abort, read data from the server.
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* 5. Upon completion, abort, or an error, the thread does the following:
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* a) close any open handles
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* b) wait for the main thread to request an exit (so the main thread can read
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* any data.)
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* c) delete the data buffer (previously allocated in this thread)
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* d) sets a flag letting the main thread know this thread is finished.
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* e) exit
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*
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* -------------------
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* Thread interaction:
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* All thread interaction is handled via a shared RequestContext_t. Interaction is
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* structured so that at all times, only one thread can be writing to any given
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* variable.
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*
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* This is an attempt to enumerate all cases of thread interaction:
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* 1. Before download thread creation
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* a) main thread allocates the RequestContext_t, and zeroes it out.
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* b) main thread fills in the baseURL and gamePath strings.
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* c) main thread sets cachedTimestamp, nBytesCached, and allocates/fills
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* cacheData if there is data from a previous aborted download.
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* 2. During thread operation:
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* a) download thread can do the following:
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* i. for HTTP_CONNECTING, download thread can set nBytesTotal,
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* nBytesCached, and nBytesCurrent. It can allocate data, and
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* set the status to HTTP_FETCH, HTTP_ABORTED, or HTTP_ERROR.
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* ii. for HTTP_FETCH, download thread can write to data, set
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* nBytesCurrent, and set status to HTTP_DONE, HTTP_ABORTED,
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* or HTTP_ERROR.
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* iii. for HTTP_DONE, HTTP_ABORTED, and HTTP_ERROR, the download thread
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* can only look at shouldStop until it is set by the main thread.
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* b) main thread can look at status.
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* i. for HTTP_CONNECTING, nothing is read, and only shouldStop can be set.
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* ii. for HTTP_FETCH, nBytesTotal and nBytesCurrent are read, and
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* shouldStop can be set.
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* iii. for HTTP_DONE, nBytesTotal, nBytesCurrent, and data are read. Also,
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* shouldStop can be set.
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* iv. for HTTP_ABORTED, nothing is read, and only shouldStop can be set.
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* v. for HTTP_ERROR, nBytesTotal, nBytesCurrent, and data are read. Also,
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* shouldStop can be set.
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* 3. After shouldStop is set by main thread:
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* a) if the download thread is in status HTTP_FETCH, it will cease operations
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* and set status to HTTP_ABORTED.
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* b) download thread will delete data, if it exists.
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* c) download thread will set threadDone.
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* d) after the main thread set shouldStop, it will only look at threadDone.
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* 4. After threadDone is set by download thread:
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* a) download thread can safely exit, and will not access the RequestContext_t.
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* b) main thread can delete the cacheData, if any exists, and delete the
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* RequestContext_t itself. Thus ends the download.
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* 5. SPECIAL CASE: if the user hits Cancel during a download, the main thread will
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* look at nBytesTotal and nBytesCurrent to determine if there is any data
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* present, and read from data if there is. The download thread will most likely
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* be in HTTP_CONNECTING or HTTP_FETCH, but could also be in HTTP_DONE or
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* HTTP_ERROR at this time. Regardless, this should be safe because of the
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* following reasons:
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* a) if nBytesCurrent is non-zero, this means data has been allocated, and
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* nBytesTotal has been set and won't change.
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* b) nBytesCurrent increases monotonically, so the contents of
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* data[0..nBytesCurrent] is complete and unchanging.
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*
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*/
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//--------------------------------------------------------------------------------------------------------------
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#include "engine/requestcontext.h"
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//--------------------------------------------------------------------------------------------------------------
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#ifdef POSIX
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void DownloadThread( void *voidPtr );
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#else
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DWORD __stdcall DownloadThread( void *voidPtr );
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#endif
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#endif // DOWNLOAD_INTERNAL_H
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//--------------------------------------------------------------------------------------------------------------
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