create a libwebputils under src/utils

with bit_reader bit_writer and thread for now. Change-Id: If961933fcfc43e60220913fe4d527230ba8f46bb
2025-08-29 15:22:12 +02:00 · 2011-09-07 09:26:35 +00:00
parent ee697d9fc9
commit b112e83647
16 changed files with 76 additions and 53 deletions
--- a/src/utils/Makefile.am
+++ b/src/utils/Makefile.am
@@ -0,0 +1,13 @@
+AM_CPPFLAGS = -I$(top_srcdir)/src
+
+libwebputils_la_SOURCES = bit_reader.h bit_reader.c \
+                          bit_writer.h bit_writer.c \
+                          thread.h thread.c
+libwebputils_la_LDFLAGS = -version-info 0:0:0
+libwebputils_la_CPPFLAGS = $(USE_EXPERIMENTAL_CODE)
+libwebputilsinclude_HEADERS = ../webp/types.h
+libwebputilsincludedir = $(includedir)/webp
+
+noinst_HEADERS = bit_reader.h bit_writer.h thread.h
+
+noinst_LTLIBRARIES = libwebputils.la
--- a/src/utils/bit_reader.c
+++ b/src/utils/bit_reader.c
@@ -0,0 +1,79 @@
+// Copyright 2010 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Boolean decoder
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include "./bit_reader.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//------------------------------------------------------------------------------
+// VP8BitReader
+
+void VP8InitBitReader(VP8BitReader* const br,
+                      const uint8_t* const start, const uint8_t* const end) {
+  assert(br);
+  assert(start);
+  assert(start <= end);
+  br->range_   = 255 - 1;
+  br->buf_     = start;
+  br->buf_end_ = end;
+  br->value_   = 0;
+  br->missing_ = 8;
+  br->eof_     = 0;
+}
+
+const uint8_t kVP8Log2Range[128] = {
+     7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
+  3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  0
+};
+
+// range = ((range + 1) << kVP8Log2Range[range]) - 1
+const uint8_t kVP8NewRange[128] = {
+  127, 127, 191, 127, 159, 191, 223, 127, 143, 159, 175, 191, 207, 223, 239,
+  127, 135, 143, 151, 159, 167, 175, 183, 191, 199, 207, 215, 223, 231, 239,
+  247, 127, 131, 135, 139, 143, 147, 151, 155, 159, 163, 167, 171, 175, 179,
+  183, 187, 191, 195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239,
+  243, 247, 251, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149,
+  151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179,
+  181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201, 203, 205, 207, 209,
+  211, 213, 215, 217, 219, 221, 223, 225, 227, 229, 231, 233, 235, 237, 239,
+  241, 243, 245, 247, 249, 251, 253, 127
+};
+
+//------------------------------------------------------------------------------
+// Higher-level calls
+
+uint32_t VP8GetValue(VP8BitReader* const br, int bits) {
+  uint32_t v = 0;
+  while (bits-- > 0) {
+    v |= VP8GetBit(br, 0x80) << bits;
+  }
+  return v;
+}
+
+int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
+  const int value = VP8GetValue(br, bits);
+  return VP8Get(br) ? -value : value;
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
--- a/src/utils/bit_reader.h
+++ b/src/utils/bit_reader.h
@@ -0,0 +1,108 @@
+// Copyright 2010 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Boolean decoder
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#ifndef WEBP_UTILS_BIT_READER_H_
+#define WEBP_UTILS_BIT_READER_H_
+
+#include <assert.h>
+#include "../webp/decode_vp8.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//------------------------------------------------------------------------------
+// Bitreader and code-tree reader
+
+typedef struct {
+  const uint8_t* buf_;        // next byte to be read
+  const uint8_t* buf_end_;    // end of read buffer
+  int eof_;                   // true if input is exhausted
+
+  // boolean decoder
+  uint32_t range_;            // current range minus 1. In [127, 254] interval.
+  uint32_t value_;            // current value
+  int missing_;               // number of missing bits in value_ (8bit)
+} VP8BitReader;
+
+// Initialize the bit reader and the boolean decoder.
+void VP8InitBitReader(VP8BitReader* const br,
+                      const uint8_t* const start, const uint8_t* const end);
+
+// return the next value made of 'num_bits' bits
+uint32_t VP8GetValue(VP8BitReader* const br, int num_bits);
+static inline uint32_t VP8Get(VP8BitReader* const br) {
+  return VP8GetValue(br, 1);
+}
+
+// return the next value with sign-extension.
+int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
+
+// Read a bit with proba 'prob'. Speed-critical function!
+extern const uint8_t kVP8Log2Range[128];
+extern const uint8_t kVP8NewRange[128];
+static inline uint32_t VP8GetByte(VP8BitReader* const br) {
+  assert(br);
+  if (br->buf_ < br->buf_end_) {
+    assert(br->buf_);
+    return *br->buf_++;
+  }
+  br->eof_ = 1;
+  return 0xff;
+}
+
+static inline uint32_t VP8BitUpdate(VP8BitReader* const br, uint32_t split) {
+  uint32_t bit;
+  const uint32_t value_split = (split + 1) << 8;
+  // Make sure we have a least 8 bits in 'value_'
+  if (br->missing_ > 0) {
+    br->value_ |= VP8GetByte(br) << br->missing_;
+    br->missing_ -= 8;
+  }
+  bit = (br->value_ >= value_split);
+  if (bit) {
+    br->range_ -= split + 1;
+    br->value_ -= value_split;
+  } else {
+    br->range_ = split;
+  }
+  return bit;
+}
+
+static inline void VP8Shift(VP8BitReader* const br) {
+  // range_ is in [0..127] interval here.
+  const int shift = kVP8Log2Range[br->range_];
+  br->range_ = kVP8NewRange[br->range_];
+  br->value_ <<= shift;
+  br->missing_ += shift;
+}
+
+static inline uint32_t VP8GetBit(VP8BitReader* const br, int prob) {
+  const uint32_t split = (br->range_ * prob) >> 8;
+  const uint32_t bit = VP8BitUpdate(br, split);
+  if (br->range_ < 0x7f) {
+    VP8Shift(br);
+  }
+  return bit;
+}
+
+static inline int VP8GetSigned(VP8BitReader* const br, int v) {
+  const uint32_t split = br->range_ >> 1;
+  const uint32_t bit = VP8BitUpdate(br, split);
+  VP8Shift(br);
+  return bit ? -v : v;
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_UTILS_BIT_READER_H_ */
--- a/src/utils/bit_writer.c
+++ b/src/utils/bit_writer.c
@@ -0,0 +1,186 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Bit writing and boolean coder
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <assert.h>
+#include <string.h>   // for memcpy()
+#include <stdlib.h>
+#include "./bit_writer.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//------------------------------------------------------------------------------
+// VP8BitWriter
+
+static int BitWriterResize(VP8BitWriter* const bw, size_t extra_size) {
+  uint8_t* new_buf;
+  size_t new_size;
+  const size_t needed_size = bw->pos_ + extra_size;
+  if (needed_size <= bw->max_pos_) return 1;
+  new_size = 2 * bw->max_pos_;
+  if (new_size < needed_size)
+    new_size = needed_size;
+  if (new_size < 1024) new_size = 1024;
+  new_buf = (uint8_t*)malloc(new_size);
+  if (new_buf == NULL) {
+    bw->error_ = 1;
+    return 0;
+  }
+  if (bw->pos_ > 0) memcpy(new_buf, bw->buf_, bw->pos_);
+  free(bw->buf_);
+  bw->buf_ = new_buf;
+  bw->max_pos_ = new_size;
+  return 1;
+}
+
+static void kFlush(VP8BitWriter* const bw) {
+  const int s = 8 + bw->nb_bits_;
+  const int32_t bits = bw->value_ >> s;
+  assert(bw->nb_bits_ >= 0);
+  bw->value_ -= bits << s;
+  bw->nb_bits_ -= 8;
+  if ((bits & 0xff) != 0xff) {
+    size_t pos = bw->pos_;
+    if (pos + bw->run_ >= bw->max_pos_) {  // reallocate
+      if (!BitWriterResize(bw,  bw->run_ + 1)) {
+        return;
+      }
+    }
+    if (bits & 0x100) {  // overflow -> propagate carry over pending 0xff's
+      if (pos > 0) bw->buf_[pos - 1]++;
+    }
+    if (bw->run_ > 0) {
+      const int value = (bits & 0x100) ? 0x00 : 0xff;
+      for (; bw->run_ > 0; --bw->run_) bw->buf_[pos++] = value;
+    }
+    bw->buf_[pos++] = bits;
+    bw->pos_ = pos;
+  } else {
+    bw->run_++;   // delay writing of bytes 0xff, pending eventual carry.
+  }
+}
+
+//------------------------------------------------------------------------------
+// renormalization
+
+static const uint8_t kNorm[128] = {  // renorm_sizes[i] = 8 - log2(i)
+     7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
+  3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  0
+};
+
+// range = ((range + 1) << kVP8Log2Range[range]) - 1
+static const uint8_t kNewRange[128] = {
+  127, 127, 191, 127, 159, 191, 223, 127, 143, 159, 175, 191, 207, 223, 239,
+  127, 135, 143, 151, 159, 167, 175, 183, 191, 199, 207, 215, 223, 231, 239,
+  247, 127, 131, 135, 139, 143, 147, 151, 155, 159, 163, 167, 171, 175, 179,
+  183, 187, 191, 195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239,
+  243, 247, 251, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149,
+  151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179,
+  181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201, 203, 205, 207, 209,
+  211, 213, 215, 217, 219, 221, 223, 225, 227, 229, 231, 233, 235, 237, 239,
+  241, 243, 245, 247, 249, 251, 253, 127
+};
+
+int VP8PutBit(VP8BitWriter* const bw, int bit, int prob) {
+  const int split = (bw->range_ * prob) >> 8;
+  if (bit) {
+    bw->value_ += split + 1;
+    bw->range_ -= split + 1;
+  } else {
+    bw->range_ = split;
+  }
+  if (bw->range_ < 127) {   // emit 'shift' bits out and renormalize
+    const int shift = kNorm[bw->range_];
+    bw->range_ = kNewRange[bw->range_];
+    bw->value_ <<= shift;
+    bw->nb_bits_ += shift;
+    if (bw->nb_bits_ > 0) kFlush(bw);
+  }
+  return bit;
+}
+
+int VP8PutBitUniform(VP8BitWriter* const bw, int bit) {
+  const int split = bw->range_ >> 1;
+  if (bit) {
+    bw->value_ += split + 1;
+    bw->range_ -= split + 1;
+  } else {
+    bw->range_ = split;
+  }
+  if (bw->range_ < 127) {
+    bw->range_ = kNewRange[bw->range_];
+    bw->value_ <<= 1;
+    bw->nb_bits_ += 1;
+    if (bw->nb_bits_ > 0) kFlush(bw);
+  }
+  return bit;
+}
+
+void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits) {
+  int mask;
+  for (mask = 1 << (nb_bits - 1); mask; mask >>= 1)
+    VP8PutBitUniform(bw, value & mask);
+}
+
+void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits) {
+  if (!VP8PutBitUniform(bw, value != 0))
+    return;
+  if (value < 0) {
+    VP8PutValue(bw, ((-value) << 1) | 1, nb_bits + 1);
+  } else {
+    VP8PutValue(bw, value << 1, nb_bits + 1);
+  }
+}
+
+//------------------------------------------------------------------------------
+
+int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size) {
+  bw->range_   = 255 - 1;
+  bw->value_   = 0;
+  bw->run_     = 0;
+  bw->nb_bits_ = -8;
+  bw->pos_     = 0;
+  bw->max_pos_ = 0;
+  bw->error_   = 0;
+  bw->buf_     = NULL;
+  return (expected_size > 0) ? BitWriterResize(bw, expected_size) : 1;
+}
+
+uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw) {
+  VP8PutValue(bw, 0, 9 - bw->nb_bits_);
+  bw->nb_bits_ = 0;   // pad with zeroes
+  kFlush(bw);
+  return bw->buf_;
+}
+
+int VP8BitWriterAppend(VP8BitWriter* const bw,
+                       const uint8_t* data, size_t size) {
+  assert(data);
+  if (bw->nb_bits_ != -8) return 0;   // kFlush() must have been called
+  if (!BitWriterResize(bw, size)) return 0;
+  memcpy(bw->buf_ + bw->pos_, data, size);
+  bw->pos_ += size;
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
--- a/src/utils/bit_writer.h
+++ b/src/utils/bit_writer.h
@@ -0,0 +1,63 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Bit writing and boolean coder
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#ifndef WEBP_UTILS_BIT_WRITER_H_
+#define WEBP_UTILS_BIT_WRITER_H_
+
+#include "../webp/types.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//------------------------------------------------------------------------------
+// Bit-writing
+
+typedef struct VP8BitWriter VP8BitWriter;
+struct VP8BitWriter {
+  int32_t  range_;      // range-1
+  int32_t  value_;
+  int      run_;        // number of outstanding bits
+  int      nb_bits_;    // number of pending bits
+  uint8_t* buf_;
+  size_t   pos_;
+  size_t   max_pos_;
+  int      error_;      // true in case of error
+};
+
+int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size);
+uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw);
+int VP8PutBit(VP8BitWriter* const bw, int bit, int prob);
+int VP8PutBitUniform(VP8BitWriter* const bw, int bit);
+void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits);
+void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits);
+int VP8BitWriterAppend(VP8BitWriter* const bw,
+                       const uint8_t* data, size_t size);
+
+// return approximate write position (in bits)
+static inline uint64_t VP8BitWriterPos(const VP8BitWriter* const bw) {
+  return (uint64_t)(bw->pos_ + bw->run_) * 8 + 8 + bw->nb_bits_;
+}
+
+static inline uint8_t* VP8BitWriterBuf(const VP8BitWriter* const bw) {
+  return bw->buf_;
+}
+static inline size_t VP8BitWriterSize(const VP8BitWriter* const bw) {
+  return bw->pos_;
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_UTILS_BIT_WRITER_H_ */
--- a/src/utils/thread.c
+++ b/src/utils/thread.c
@@ -0,0 +1,243 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Multi-threaded worker
+//
+// Author: skal@google.com (Pascal Massimino)
+
+#include <assert.h>
+#include <string.h>   // for memset()
+#include "./thread.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#ifdef WEBP_USE_THREAD
+
+#if defined(_WIN32)
+
+//------------------------------------------------------------------------------
+// simplistic pthread emulation layer
+
+#include <process.h>
+
+// _beginthreadex requires __stdcall
+#define THREADFN unsigned int __stdcall
+#define THREAD_RETURN(val) (unsigned int)((DWORD_PTR)val)
+
+static int pthread_create(pthread_t* const thread, const void* attr,
+                          unsigned int (__stdcall *start)(void*), void* arg) {
+  (void)attr;
+  *thread = (pthread_t)_beginthreadex(NULL,   /* void *security */
+                                      0,      /* unsigned stack_size */
+                                      start,
+                                      arg,
+                                      0,      /* unsigned initflag */
+                                      NULL);  /* unsigned *thrdaddr */
+  if (*thread == NULL) return 1;
+  SetThreadPriority(*thread, THREAD_PRIORITY_ABOVE_NORMAL);
+  return 0;
+}
+
+static int pthread_join(pthread_t thread, void** value_ptr) {
+  (void)value_ptr;
+  return (WaitForSingleObject(thread, INFINITE) != WAIT_OBJECT_0 ||
+          CloseHandle(thread) == 0);
+}
+
+// Mutex
+static int pthread_mutex_init(pthread_mutex_t* const mutex, void* mutexattr) {
+  (void)mutexattr;
+  InitializeCriticalSection(mutex);
+  return 0;
+}
+
+static int pthread_mutex_lock(pthread_mutex_t* const mutex) {
+  EnterCriticalSection(mutex);
+  return 0;
+}
+
+static int pthread_mutex_unlock(pthread_mutex_t* const mutex) {
+  LeaveCriticalSection(mutex);
+  return 0;
+}
+
+static int pthread_mutex_destroy(pthread_mutex_t* const mutex) {
+  DeleteCriticalSection(mutex);
+  return 0;
+}
+
+// Condition
+static int pthread_cond_destroy(pthread_cond_t* const condition) {
+  int ok = 1;
+  ok &= (CloseHandle(condition->waiting_sem_) == 0);
+  ok &= (CloseHandle(condition->received_sem_) == 0);
+  ok &= (CloseHandle(condition->signal_event_) == 0);
+  return ok;
+}
+
+static int pthread_cond_init(pthread_cond_t* const condition, void* cond_attr) {
+  (void)cond_attr;
+  condition->waiting_sem_ = CreateSemaphore(NULL, 0, 1, NULL);
+  condition->received_sem_ = CreateSemaphore(NULL, 0, 1, NULL);
+  condition->signal_event_ = CreateEvent(NULL, FALSE, FALSE, NULL);
+  if (condition->waiting_sem_ == NULL ||
+      condition->received_sem_ == NULL ||
+      condition->signal_event_ == NULL) {
+    pthread_cond_destroy(condition);
+    return 1;
+  }
+  return 0;
+}
+
+static int pthread_cond_signal(pthread_cond_t* const condition) {
+  int ok = 1;
+  if (WaitForSingleObject(condition->waiting_sem_, 0) == WAIT_OBJECT_0) {
+    // a thread is waiting in pthread_cond_wait: allow it to be notified
+    ok = SetEvent(condition->signal_event_);
+    // wait until the event is consumed so the signaler cannot consume
+    // the event via its own pthread_cond_wait.
+    ok &= (WaitForSingleObject(condition->received_sem_, INFINITE) !=
+           WAIT_OBJECT_0);
+  }
+  return !ok;
+}
+
+static int pthread_cond_wait(pthread_cond_t* const condition,
+                             pthread_mutex_t* const mutex) {
+  int ok;
+  // note that there is a consumer available so the signal isn't dropped in
+  // pthread_cond_signal
+  if (!ReleaseSemaphore(condition->waiting_sem_, 1, NULL))
+    return 1;
+  // now unlock the mutex so pthread_cond_signal may be issued
+  pthread_mutex_unlock(mutex);
+  ok = (WaitForSingleObject(condition->signal_event_, INFINITE) ==
+        WAIT_OBJECT_0);
+  ok &= ReleaseSemaphore(condition->received_sem_, 1, NULL);
+  pthread_mutex_lock(mutex);
+  return !ok;
+}
+
+#else  // _WIN32
+# define THREADFN void*
+# define THREAD_RETURN(val) val
+#endif
+
+//------------------------------------------------------------------------------
+
+static THREADFN WebPWorkerThreadLoop(void *ptr) {    // thread loop
+  WebPWorker* const worker = (WebPWorker*)ptr;
+  int done = 0;
+  while (!done) {
+    pthread_mutex_lock(&worker->mutex_);
+    while (worker->status_ == OK) {   // wait in idling mode
+      pthread_cond_wait(&worker->condition_, &worker->mutex_);
+    }
+    if (worker->status_ == WORK) {
+      if (worker->hook) {
+        worker->had_error |= !worker->hook(worker->data1, worker->data2);
+      }
+      worker->status_ = OK;
+    } else if (worker->status_ == NOT_OK) {   // finish the worker
+      done = 1;
+    }
+    // signal to the main thread that we're done (for Sync())
+    pthread_cond_signal(&worker->condition_);
+    pthread_mutex_unlock(&worker->mutex_);
+  }
+  return THREAD_RETURN(NULL);    // Thread is finished
+}
+
+// main thread state control
+static void WebPWorkerChangeState(WebPWorker* const worker,
+                                  WebPWorkerStatus new_status) {
+  // no-op when attempting to change state on a thread that didn't come up
+  if (worker->status_ < OK) return;
+
+  pthread_mutex_lock(&worker->mutex_);
+  // wait for the worker to finish
+  while (worker->status_ != OK) {
+    pthread_cond_wait(&worker->condition_, &worker->mutex_);
+  }
+  // assign new status and release the working thread if needed
+  if (new_status != OK) {
+    worker->status_ = new_status;
+    pthread_cond_signal(&worker->condition_);
+  }
+  pthread_mutex_unlock(&worker->mutex_);
+}
+
+#endif
+
+//------------------------------------------------------------------------------
+
+void WebPWorkerInit(WebPWorker* const worker) {
+  memset(worker, 0, sizeof(*worker));
+  worker->status_ = NOT_OK;
+}
+
+int WebPWorkerSync(WebPWorker* const worker) {
+#ifdef WEBP_USE_THREAD
+  WebPWorkerChangeState(worker, OK);
+#endif
+  assert(worker->status_ <= OK);
+  return !worker->had_error;
+}
+
+int WebPWorkerReset(WebPWorker* const worker) {
+  int ok = 1;
+  worker->had_error = 0;
+  if (worker->status_ < OK) {
+#ifdef WEBP_USE_THREAD
+    if (pthread_mutex_init(&worker->mutex_, NULL) ||
+        pthread_cond_init(&worker->condition_, NULL)) {
+      return 0;
+    }
+    pthread_mutex_lock(&worker->mutex_);
+    ok = !pthread_create(&worker->thread_, NULL, WebPWorkerThreadLoop, worker);
+    if (ok) worker->status_ = OK;
+    pthread_mutex_unlock(&worker->mutex_);
+#else
+    worker->status_ = OK;
+#endif
+  } else if (worker->status_ > OK) {
+    ok = WebPWorkerSync(worker);
+  }
+  assert(!ok || (worker->status_ == OK));
+  return ok;
+}
+
+void WebPWorkerLaunch(WebPWorker* const worker) {
+#ifdef WEBP_USE_THREAD
+  WebPWorkerChangeState(worker, WORK);
+#else
+  if (worker->hook)
+    worker->had_error |= !worker->hook(worker->data1, worker->data2);
+#endif
+}
+
+void WebPWorkerEnd(WebPWorker* const worker) {
+  if (worker->status_ >= OK) {
+#ifdef WEBP_USE_THREAD
+    WebPWorkerChangeState(worker, NOT_OK);
+    pthread_join(worker->thread_, NULL);
+    pthread_mutex_destroy(&worker->mutex_);
+    pthread_cond_destroy(&worker->condition_);
+#else
+    worker->status_ = NOT_OK;
+#endif
+  }
+  assert(worker->status_ == NOT_OK);
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
--- a/src/utils/thread.h
+++ b/src/utils/thread.h
@@ -0,0 +1,86 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Multi-threaded worker
+//
+// Author: skal@google.com (Pascal Massimino)
+
+#ifndef WEBP_UTILS_THREAD_H_
+#define WEBP_UTILS_THREAD_H_
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#if WEBP_USE_THREAD
+
+#if defined(_WIN32)
+
+#include <windows.h>
+typedef HANDLE pthread_t;
+typedef CRITICAL_SECTION pthread_mutex_t;
+typedef struct {
+  HANDLE waiting_sem_;
+  HANDLE received_sem_;
+  HANDLE signal_event_;
+} pthread_cond_t;
+
+#else
+
+#include <pthread.h>
+
+#endif    /* _WIN32 */
+#endif    /* WEBP_USE_THREAD */
+
+// State of the worker thread object
+typedef enum {
+  NOT_OK = 0,   // object is unusable
+  OK,           // ready to work
+  WORK          // busy finishing the current task
+} WebPWorkerStatus;
+
+// Function to be called by the worker thread. Takes two opaque pointers as
+// arguments (data1 and data2), and should return false in case of error.
+typedef int (*WebPWorkerHook)(void*, void*);
+
+// Synchronize object used to launch job in the worker thread
+typedef struct {
+#if WEBP_USE_THREAD
+  pthread_mutex_t mutex_;
+  pthread_cond_t  condition_;
+  pthread_t       thread_;
+#endif
+  WebPWorkerStatus status_;
+  WebPWorkerHook hook;    // hook to call
+  void* data1;            // first argument passed to 'hook'
+  void* data2;            // second argument passed to 'hook'
+  int had_error;          // return value of the last call to 'hook'
+} WebPWorker;
+
+// Must be called first, before any other method.
+void WebPWorkerInit(WebPWorker* const worker);
+// Must be called initialize the object and spawn the thread. Re-entrant.
+// Will potentially launch the thread. Returns false in case of error.
+int WebPWorkerReset(WebPWorker* const worker);
+// Make sure the previous work is finished. Returns true if worker->had_error
+// was not set and not error condition was triggered by the working thread.
+int WebPWorkerSync(WebPWorker* const worker);
+// Trigger the thread to call hook() with data1 and data2 argument. These
+// hook/data1/data2 can be changed at any time before calling this function,
+// but not be changed afterward until the next call to WebPWorkerSync().
+void WebPWorkerLaunch(WebPWorker* const worker);
+// Kill the thread and terminate the object. To use the object again, one
+// must call WebPWorkerReset() again.
+void WebPWorkerEnd(WebPWorker* const worker);
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_UTILS_THREAD_H_ */