The Tor Browser: content/media/FileBlockCache.cpp@44a2da4a2ab2 (annotated)

content/media/FileBlockCache.cpp@44a2da4a2ab2 (annotated)

content/media/FileBlockCache.cpp

Fri, 16 Jan 2015 04:50:19 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 04:50:19 +0100
branch: TOR_BUG_9701
changeset 13: 44a2da4a2ab2
permissions: -rw-r--r--

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "FileBlockCache.h"
 #include "VideoUtils.h"
 #include "prio.h"
 #include <algorithm>
 namespace mozilla {
 nsresult FileBlockCache::Open(PRFileDesc* aFD)
 {
   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
   NS_ENSURE_TRUE(aFD != nullptr, NS_ERROR_FAILURE);
   {
     MonitorAutoLock mon(mFileMonitor);
     mFD = aFD;
   }
   {
     MonitorAutoLock mon(mDataMonitor);
     nsresult res = NS_NewThread(getter_AddRefs(mThread),
                                 nullptr,
                                 MEDIA_THREAD_STACK_SIZE);
     mIsOpen = NS_SUCCEEDED(res);
     return res;
   }
 }
 FileBlockCache::FileBlockCache()
   : mFileMonitor("MediaCache.Writer.IO.Monitor"),
     mFD(nullptr),
     mFDCurrentPos(0),
     mDataMonitor("MediaCache.Writer.Data.Monitor"),
     mIsWriteScheduled(false),
     mIsOpen(false)
 {
   MOZ_COUNT_CTOR(FileBlockCache);
 }
 FileBlockCache::~FileBlockCache()
 {
   NS_ASSERTION(!mIsOpen, "Should Close() FileBlockCache before destroying");
   {
     // Note, mThread will be shutdown by the time this runs, so we won't
     // block while taking mFileMonitor.
     MonitorAutoLock mon(mFileMonitor);
     if (mFD) {
       PRStatus prrc;
       prrc = PR_Close(mFD);
       if (prrc != PR_SUCCESS) {
         NS_WARNING("PR_Close() failed.");
       }
       mFD = nullptr;
     }
   }
   MOZ_COUNT_DTOR(FileBlockCache);
 }
 void FileBlockCache::Close()
 {
   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
   MonitorAutoLock mon(mDataMonitor);
   mIsOpen = false;
   if (mThread) {
     // We must shut down the thread in another runnable. This is called
     // while we're shutting down the media cache, and nsIThread::Shutdown()
     // can cause events to run before it completes, which could end up
     // opening more streams, while the media cache is shutting down and
     // releasing memory etc! Also note we close mFD in the destructor so
     // as to not disturb any IO that's currently running.
     nsCOMPtr<nsIRunnable> event = new ShutdownThreadEvent(mThread);
     mThread = nullptr;
     NS_DispatchToMainThread(event);
   }
 }
 nsresult FileBlockCache::WriteBlock(uint32_t aBlockIndex, const uint8_t* aData)
 {
   MonitorAutoLock mon(mDataMonitor);
   if (!mIsOpen)
     return NS_ERROR_FAILURE;
   // Check if we've already got a pending write scheduled for this block.
   mBlockChanges.EnsureLengthAtLeast(aBlockIndex + 1);
   bool blockAlreadyHadPendingChange = mBlockChanges[aBlockIndex] != nullptr;
   mBlockChanges[aBlockIndex] = new BlockChange(aData);
   if (!blockAlreadyHadPendingChange || !mChangeIndexList.Contains(aBlockIndex)) {
     // We either didn't already have a pending change for this block, or we
     // did but we didn't have an entry for it in mChangeIndexList (we're in the process
     // of writing it and have removed the block's index out of mChangeIndexList
     // in Run() but not finished writing the block to file yet). Add the blocks
     // index to the end of mChangeIndexList to ensure the block is written as
     // as soon as possible.
     mChangeIndexList.PushBack(aBlockIndex);
   }
   NS_ASSERTION(mChangeIndexList.Contains(aBlockIndex), "Must have entry for new block");
   EnsureWriteScheduled();
   return NS_OK;
 }
 void FileBlockCache::EnsureWriteScheduled()
 {
   mDataMonitor.AssertCurrentThreadOwns();
   if (!mIsWriteScheduled) {
     mThread->Dispatch(this, NS_DISPATCH_NORMAL);
     mIsWriteScheduled = true;
   }
 }
 nsresult FileBlockCache::Seek(int64_t aOffset)
 {
   mFileMonitor.AssertCurrentThreadOwns();
   if (mFDCurrentPos != aOffset) {
     int64_t result = PR_Seek64(mFD, aOffset, PR_SEEK_SET);
     if (result != aOffset) {
       NS_WARNING("Failed to seek media cache file");
       return NS_ERROR_FAILURE;
     }
     mFDCurrentPos = result;
   }
   return NS_OK;
 }
 nsresult FileBlockCache::ReadFromFile(int64_t aOffset,
                                       uint8_t* aDest,
                                       int32_t aBytesToRead,
                                       int32_t& aBytesRead)
 {
   mFileMonitor.AssertCurrentThreadOwns();
   nsresult res = Seek(aOffset);
   if (NS_FAILED(res)) return res;
   aBytesRead = PR_Read(mFD, aDest, aBytesToRead);
   if (aBytesRead <= 0)
     return NS_ERROR_FAILURE;
   mFDCurrentPos += aBytesRead;
   return NS_OK;
 }
 nsresult FileBlockCache::WriteBlockToFile(int32_t aBlockIndex,
                                           const uint8_t* aBlockData)
 {
   mFileMonitor.AssertCurrentThreadOwns();
   nsresult rv = Seek(BlockIndexToOffset(aBlockIndex));
   if (NS_FAILED(rv)) return rv;
   int32_t amount = PR_Write(mFD, aBlockData, BLOCK_SIZE);
   if (amount < BLOCK_SIZE) {
     NS_WARNING("Failed to write media cache block!");
     return NS_ERROR_FAILURE;
   }
   mFDCurrentPos += BLOCK_SIZE;
   return NS_OK;
 }
 nsresult FileBlockCache::MoveBlockInFile(int32_t aSourceBlockIndex,
                                          int32_t aDestBlockIndex)
 {
   mFileMonitor.AssertCurrentThreadOwns();
   uint8_t buf[BLOCK_SIZE];
   int32_t bytesRead = 0;
   if (NS_FAILED(ReadFromFile(BlockIndexToOffset(aSourceBlockIndex),
                              buf,
                              BLOCK_SIZE,
                              bytesRead))) {
     return NS_ERROR_FAILURE;
   }
   return WriteBlockToFile(aDestBlockIndex, buf);
 }
 nsresult FileBlockCache::Run()
 {
   MonitorAutoLock mon(mDataMonitor);
   NS_ASSERTION(!NS_IsMainThread(), "Don't call on main thread");
   NS_ASSERTION(!mChangeIndexList.IsEmpty(), "Only dispatch when there's work to do");
   NS_ASSERTION(mIsWriteScheduled, "Should report write running or scheduled.");
   while (!mChangeIndexList.IsEmpty()) {
     if (!mIsOpen) {
       // We've been closed, abort, discarding unwritten changes.
       mIsWriteScheduled = false;
       return NS_ERROR_FAILURE;
     }
     // Process each pending change. We pop the index out of the change
     // list, but leave the BlockChange in mBlockChanges until the change
     // is written to file. This is so that any read which happens while
     // we drop mDataMonitor to write will refer to the data's source in
     // memory, rather than the not-yet up to date data written to file.
     // This also ensures we will insert a new index into mChangeIndexList
     // when this happens.
     // Hold a reference to the change, in case another change
     // overwrites the mBlockChanges entry for this block while we drop
     // mDataMonitor to take mFileMonitor.
     int32_t blockIndex = mChangeIndexList.PopFront();
     nsRefPtr<BlockChange> change = mBlockChanges[blockIndex];
     NS_ABORT_IF_FALSE(change,
       "Change index list should only contain entries for blocks with changes");
     {
       MonitorAutoUnlock unlock(mDataMonitor);
       MonitorAutoLock lock(mFileMonitor);
       if (change->IsWrite()) {
         WriteBlockToFile(blockIndex, change->mData.get());
       } else if (change->IsMove()) {
         MoveBlockInFile(change->mSourceBlockIndex, blockIndex);
       }
     }
     // If a new change has not been made to the block while we dropped
     // mDataMonitor, clear reference to the old change. Otherwise, the old
     // reference has been cleared already.
     if (mBlockChanges[blockIndex] == change) {
       mBlockChanges[blockIndex] = nullptr;
     }
   }
   mIsWriteScheduled = false;
   return NS_OK;
 }
 nsresult FileBlockCache::Read(int64_t aOffset,
                               uint8_t* aData,
                               int32_t aLength,
                               int32_t* aBytes)
 {
   MonitorAutoLock mon(mDataMonitor);
   if (!mFD || (aOffset / BLOCK_SIZE) > INT32_MAX)
     return NS_ERROR_FAILURE;
   int32_t bytesToRead = aLength;
   int64_t offset = aOffset;
   uint8_t* dst = aData;
   while (bytesToRead > 0) {
     int32_t blockIndex = static_cast<int32_t>(offset / BLOCK_SIZE);
     int32_t start = offset % BLOCK_SIZE;
     int32_t amount = std::min(BLOCK_SIZE - start, bytesToRead);
     // If the block is not yet written to file, we can just read from
     // the memory buffer, otherwise we need to read from file.
     int32_t bytesRead = 0;
     nsRefPtr<BlockChange> change = mBlockChanges[blockIndex];
     if (change && change->IsWrite()) {
       // Block isn't yet written to file. Read from memory buffer.
       const uint8_t* blockData = change->mData.get();
       memcpy(dst, blockData + start, amount);
       bytesRead = amount;
     } else {
       if (change && change->IsMove()) {
         // The target block is the destination of a not-yet-completed move
         // action, so read from the move's source block from file. Note we
         // *don't* follow a chain of moves here, as a move's source index
         // is resolved when MoveBlock() is called, and the move's source's
         // block could be have itself been subject to a move (or write)
         // which happened *after* this move was recorded.
         blockIndex = mBlockChanges[blockIndex]->mSourceBlockIndex;
       }
       // Block has been written to file, either as the source block of a move,
       // or as a stable (all changes made) block. Read the data directly
       // from file.
       nsresult res;
       {
         MonitorAutoUnlock unlock(mDataMonitor);
         MonitorAutoLock lock(mFileMonitor);
         res = ReadFromFile(BlockIndexToOffset(blockIndex) + start,
                            dst,
                            amount,
                            bytesRead);
       }
       NS_ENSURE_SUCCESS(res,res);
     }
     dst += bytesRead;
     offset += bytesRead;
     bytesToRead -= bytesRead;
   }
   *aBytes = aLength - bytesToRead;
   return NS_OK;
 }
 nsresult FileBlockCache::MoveBlock(int32_t aSourceBlockIndex, int32_t aDestBlockIndex)
 {
   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
   MonitorAutoLock mon(mDataMonitor);
   if (!mIsOpen)
     return NS_ERROR_FAILURE;
   mBlockChanges.EnsureLengthAtLeast(std::max(aSourceBlockIndex, aDestBlockIndex) + 1);
   // The source block's contents may be the destination of another pending
   // move, which in turn can be the destination of another pending move,
   // etc. Resolve the final source block, so that if one of the blocks in
   // the chain of moves is overwritten, we don't lose the reference to the
   // contents of the destination block.
   int32_t sourceIndex = aSourceBlockIndex;
   BlockChange* sourceBlock = nullptr;
   while ((sourceBlock = mBlockChanges[sourceIndex]) &&
           sourceBlock->IsMove()) {
     sourceIndex = sourceBlock->mSourceBlockIndex;
   }
   if (mBlockChanges[aDestBlockIndex] == nullptr ||
       !mChangeIndexList.Contains(aDestBlockIndex)) {
     // Only add another entry to the change index list if we don't already
     // have one for this block. We won't have an entry when either there's
     // no pending change for this block, or if there is a pending change for
     // this block and we're in the process of writing it (we've popped the
     // block's index out of mChangeIndexList in Run() but not finished writing
     // the block to file yet.
     mChangeIndexList.PushBack(aDestBlockIndex);
   }
   // If the source block hasn't yet been written to file then the dest block
   // simply contains that same write. Resolve this as a write instead.
   if (sourceBlock && sourceBlock->IsWrite()) {
     mBlockChanges[aDestBlockIndex] = new BlockChange(sourceBlock->mData.get());
   } else {
     mBlockChanges[aDestBlockIndex] = new BlockChange(sourceIndex);
   }
   EnsureWriteScheduled();
   NS_ASSERTION(mChangeIndexList.Contains(aDestBlockIndex),
     "Should have scheduled block for change");
   return NS_OK;
 }
 } // End namespace mozilla.

The Tor Browser / annotate

content/media/FileBlockCache.cpp@44a2da4a2ab2 (annotated)

content/media/FileBlockCache.cpp