mojo/shell/data_pipe_peek.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "mojo/shell/data_pipe_peek.h"
   6
   7 #include <stdint.h>
   8
   9 #include "base/bind.h"
  10 #include "base/macros.h"
  11
  12 namespace mojo {
  13 namespace shell {
  14
  15 namespace {
  16
  17 // Sleep for as long as max_sleep_micros if the deadline hasn't been reached
  18 // and the number of bytes read is still increasing. Returns true if sleep
  19 // was actually called.
  20 //
  21 // This class is a substitute for being able to wait until N bytes are available
  22 // from a data pipe. The MaybeSleep method is called when num_bytes_read are
  23 // available but more are needed by the Peek operation. If a second
  24 // Peek operation finds the same number of bytes after sleeping we assume
  25 // that there's no point in trying again.
  26 // TODO(hansmuller): this heuristic is weak. crbug.com/429377
  27 class PeekSleeper {
  28  public:
  29   explicit PeekSleeper(MojoTimeTicks deadline)
  30       : deadline_(deadline),
  31         last_number_bytes_read_(0) {}
  32
  33   bool MaybeSleep(uint32_t num_bytes_read) {
  34     if (num_bytes_read > 0 && last_number_bytes_read_ >= num_bytes_read)
  35       return false;
  36     last_number_bytes_read_ = num_bytes_read;
  37
  38     MojoTimeTicks now(GetTimeTicksNow());
  39     if (now > deadline_)
  40       return false;
  41
  42     MojoTimeTicks sleep_time =
  43         (deadline_ == 0) ? kMaxSleepMicros
  44                          : std::min<int64>(deadline_ - now, kMaxSleepMicros);
  45     base::PlatformThread::Sleep(base::TimeDelta::FromMicroseconds(sleep_time));
  46     return true;
  47   }
  48
  49  private:
  50   static const MojoTimeTicks kMaxSleepMicros = 1000 * 10;  // 10 ms
  51
  52   const MojoTimeTicks deadline_;  // 0 => MOJO_DEADLINE_INDEFINITE
  53   uint32_t last_number_bytes_read_;
  54
  55   DISALLOW_COPY_AND_ASSIGN(PeekSleeper);
  56 };
  57
  58 const MojoTimeTicks PeekSleeper::kMaxSleepMicros;
  59
  60 enum PeekStatus { kSuccess, kFail, kKeepReading };
  61 typedef const base::Callback<PeekStatus(const void*, uint32_t, std::string*)>&
  62     PeekFunc;
  63
  64 // When data is available on source, call peek_func and then either return true
  65 // and value, continue waiting for enough data to satisfy peek_func, or fail
  66 // and return false. Fail if the timeout is exceeded.
  67 // This function is not guaranteed to work correctly if applied to a data pipe
  68 // that's already been read from.
  69 bool BlockingPeekHelper(DataPipeConsumerHandle source,
  70                         std::string* value,
  71                         MojoDeadline timeout,
  72                         PeekFunc peek_func) {
  73   DCHECK(value);
  74   value->clear();
  75
  76   MojoTimeTicks deadline =
  77       (timeout == MOJO_DEADLINE_INDEFINITE)
  78           ? 0
  79           : 1 + GetTimeTicksNow() + static_cast<MojoTimeTicks>(timeout);
  80   PeekSleeper sleeper(deadline);
  81
  82   MojoResult result;
  83   do {
  84     const void* buffer;
  85     uint32_t num_bytes;
  86     result =
  87         BeginReadDataRaw(source, &buffer, &num_bytes, MOJO_READ_DATA_FLAG_NONE);
  88
  89     if (result == MOJO_RESULT_OK) {
  90       PeekStatus status = peek_func.Run(buffer, num_bytes, value);
  91       CHECK_EQ(EndReadDataRaw(source, 0), MOJO_RESULT_OK);
  92       switch (status) {
  93         case PeekStatus::kSuccess:
  94           return true;
  95         case PeekStatus::kFail:
  96           return false;
  97         case PeekStatus::kKeepReading:
  98           break;
  99       }
 100       if (!sleeper.MaybeSleep(num_bytes))
 101         return false;
 102     } else if (result == MOJO_RESULT_SHOULD_WAIT) {
 103       MojoTimeTicks now(GetTimeTicksNow());
 104       if (timeout == MOJO_DEADLINE_INDEFINITE || now < deadline)
 105         result =
 106             Wait(source, MOJO_HANDLE_SIGNAL_READABLE, deadline - now, nullptr);
 107     }
 108   } while (result == MOJO_RESULT_OK);
 109
 110   return false;
 111 }
 112
 113 PeekStatus PeekLine(size_t max_line_length,
 114                     const void* buffer,
 115                     uint32_t buffer_num_bytes,
 116                     std::string* line) {
 117   const char* p = static_cast<const char*>(buffer);
 118   size_t max_p_index = std::min<size_t>(buffer_num_bytes, max_line_length);
 119   for (size_t i = 0; i < max_p_index; i++) {
 120     if (p[i] == '\n') {
 121       *line = std::string(p, i + 1);  // Include the trailing newline.
 122       return PeekStatus::kSuccess;
 123     }
 124   }
 125   return (buffer_num_bytes >= max_line_length) ? PeekStatus::kFail
 126                                                : PeekStatus::kKeepReading;
 127 }
 128
 129 PeekStatus PeekNBytes(size_t bytes_length,
 130                       const void* buffer,
 131                       uint32_t buffer_num_bytes,
 132                       std::string* bytes) {
 133   if (buffer_num_bytes >= bytes_length) {
 134     const char* p = static_cast<const char*>(buffer);
 135     *bytes = std::string(p, bytes_length);
 136     return PeekStatus::kSuccess;
 137   }
 138   return PeekStatus::kKeepReading;
 139 }
 140
 141 }  // namespace
 142
 143 bool BlockingPeekNBytes(DataPipeConsumerHandle source,
 144                         std::string* bytes,
 145                         size_t bytes_length,
 146                         MojoDeadline timeout) {
 147   PeekFunc peek_nbytes = base::Bind(PeekNBytes, bytes_length);
 148   return BlockingPeekHelper(source, bytes, timeout, peek_nbytes);
 149 }
 150
 151 bool BlockingPeekLine(DataPipeConsumerHandle source,
 152                       std::string* line,
 153                       size_t max_line_length,
 154                       MojoDeadline timeout) {
 155   PeekFunc peek_line = base::Bind(PeekLine, max_line_length);
 156   return BlockingPeekHelper(source, line, timeout, peek_line);
 157 }
 158
 159 }  // namespace shell
 160 }  // namespace mojo