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Modernize SkMutex and SkSemaphore.

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- use <atomic>
   - fuse SkMutex and SkBaseMutex
   - fuse SkSemaphore and SkBaseSemaphore

Still TODO:
   - replace SK_DECLARE_STATIC_MUTEX(name) with static SkMutex name

I just didn't want to bother fixing all that up until I know this CL sticks.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1947153002

No public API changes.
TBR=reed@google.com

Review-Url: https://codereview.chromium.org/1947153002
This commit is contained in:
mtklein 2016-05-04 11:31:29 -07:00 committed by Commit bot
parent 325474dd42
commit 427c2819d9
7 changed files with 75 additions and 139 deletions
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2
include/core/SkPixelRef.h
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@ -342,7 +342,7 @@ protected:
/** Return the mutex associated with this pixelref. This value is assigned
in the constructor, and cannot change during the lifetime of the object.
*/
SkBaseMutex* mutex() const { return &fMutex; }
SkMutex* mutex() const { return &fMutex; }
// only call from constructor. Flags this to always be locked, removing
// the need to grab the mutex and call onLockPixels/onUnlockPixels.

1
include/ports/SkFontConfigInterface.h
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@ -13,7 +13,6 @@
#include "SkRefCnt.h"
#include "SkTypeface.h"
struct SkBaseMutex;
class SkFontMgr;
/**

50
include/private/SkMutex.h
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@ -8,33 +8,20 @@
#ifndef SkMutex_DEFINED
#define SkMutex_DEFINED
// This file is not part of the public Skia API.
#include "../private/SkSemaphore.h"
#include "../private/SkThreadID.h"
#include "SkTypes.h"
#ifdef SK_DEBUG
#include "../private/SkThreadID.h"
#endif
// TODO: no need for this anymore.
#define SK_DECLARE_STATIC_MUTEX(name) static SkMutex name;
#define SK_MUTEX_SEMAPHORE_INIT {1, {0}}
class SkMutex {
public:
constexpr SkMutex() = default;
#ifdef SK_DEBUG
#define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0}
#else
#define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT}
#endif
SkMutex(const SkMutex&) = delete;
SkMutex& operator=(const SkMutex&) = delete;
// Using POD-style initialization prevents the generation of a static initializer.
//
// Without magic statics there are no thread safety guarantees on initialization
// of local statics (even POD). As a result, it is illegal to use
// SK_DECLARE_STATIC_MUTEX in a function.
//
// Because SkBaseMutex is not a primitive, a static SkBaseMutex cannot be
// initialized in a class with this macro.
#define SK_DECLARE_STATIC_MUTEX(name) namespace {} static SkBaseMutex name = SK_BASE_MUTEX_INIT;
struct SkBaseMutex {
void acquire() {
fSemaphore.wait();
SkDEBUGCODE(fOwner = SkGetThreadID();)
@ -50,20 +37,9 @@ struct SkBaseMutex {
SkASSERT(fOwner == SkGetThreadID());
}
SkBaseSemaphore fSemaphore;
SkDEBUGCODE(SkThreadID fOwner;)
};
// This needs to use subclassing instead of encapsulation to make SkAutoMutexAcquire to work.
class SkMutex : public SkBaseMutex {
public:
SkMutex () {
fSemaphore = SK_MUTEX_SEMAPHORE_INIT;
SkDEBUGCODE(fOwner = kIllegalThreadID);
}
~SkMutex () { fSemaphore.deleteSemaphore(); }
SkMutex(const SkMutex&) = delete;
SkMutex& operator=(const SkMutex&) = delete;
private:
SkSemaphore fSemaphore{1};
SkDEBUGCODE(SkThreadID fOwner{kIllegalThreadID};)
};
template <typename Lock>
@ -116,10 +92,10 @@ private:
Lock &fLock;
};
typedef SkAutoTAcquire<SkBaseMutex> SkAutoMutexAcquire;
typedef SkAutoTAcquire<SkMutex> SkAutoMutexAcquire;
#define SkAutoMutexAcquire(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexAcquire)
typedef SkAutoTExclusive<SkBaseMutex> SkAutoMutexExclusive;
typedef SkAutoTExclusive<SkMutex> SkAutoMutexExclusive;
#define SkAutoMutexExclusive(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexExclusive)
#endif//SkMutex_DEFINED

96
include/private/SkSemaphore.h
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@ -8,43 +8,26 @@
#ifndef SkSemaphore_DEFINED
#define SkSemaphore_DEFINED
#include "../private/SkOnce.h"
#include "SkTypes.h"
#include "../private/SkAtomics.h"
#include "../private/SkOncePtr.h"
#include <atomic>
struct SkBaseSemaphore {
class SkSemaphore {
public:
constexpr SkSemaphore(int count = 0)
: fCount(count), fOSSemaphore(nullptr) {}
// Increment the counter by 1.
// This is a specialization for supporting SkMutex.
void signal() {
// Since this fetches the value before the add, 0 indicates that this thread is running and
// no threads are waiting, -1 and below means that threads are waiting, but only signal 1
// thread to run.
if (sk_atomic_fetch_add(&fCount, 1, sk_memory_order_release) < 0) {
this->osSignal(1);
}
}
~SkSemaphore();
// Increment the counter N times.
// Generally it's better to call signal(N) instead of signal() N times.
void signal(int N);
// Increment the counter n times.
// Generally it's better to call signal(n) instead of signal() n times.
void signal(int n = 1);
// Decrement the counter by 1,
// then if the counter is <= 0, sleep this thread until the counter is > 0.
void wait() {
// Since this fetches the value before the subtract, zero and below means that there are no
// resources left, so the thread needs to wait.
if (sk_atomic_fetch_sub(&fCount, 1, sk_memory_order_acquire) <= 0) {
this->osWait();
}
}
struct OSSemaphore;
void osSignal(int n);
void osWait();
void deleteSemaphore();
void wait();
private:
// This implementation follows the general strategy of
// 'A Lightweight Semaphore with Partial Spinning'
// found here
@ -54,33 +37,40 @@ struct SkBaseSemaphore {
// We wrap an OS-provided semaphore with a user-space atomic counter that
// lets us avoid interacting with the OS semaphore unless strictly required:
// moving the count from >0 to <=0 or vice-versa, i.e. sleeping or waking threads.
int fCount;
SkBaseOncePtr<OSSemaphore> fOSSemaphore;
struct OSSemaphore;
void osSignal(int n);
void osWait();
std::atomic<int> fCount;
SkOnce fOSSemaphoreOnce;
OSSemaphore* fOSSemaphore;
};
/**
* SkSemaphore is a fast mostly-user-space semaphore.
*
* A semaphore is logically an atomic integer with a few special properties:
* - The integer always starts at 0.
* - You can only increment or decrement it, never read or write it.
* - Increment is spelled 'signal()'; decrement is spelled 'wait()'.
* - If a call to wait() decrements the counter to <= 0,
* the calling thread sleeps until another thread signal()s it back above 0.
*/
class SkSemaphore : SkNoncopyable {
public:
// Initializes the counter to 0.
// (Though all current implementations could start from an arbitrary value.)
SkSemaphore();
~SkSemaphore();
inline void SkSemaphore::signal(int n) {
int prev = fCount.fetch_add(n, std::memory_order_release);
void wait();
// We only want to call the OS semaphore when our logical count crosses
// from <= 0 to >0 (when we need to wake sleeping threads).
//
// This is easiest to think about with specific examples of prev and n.
// If n == 5 and prev == -3, there are 3 threads sleeping and we signal
// SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2.
//
// If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0,
// so we don't call the OS semaphore, leaving the count at (prev + n).
int toSignal = SkTMin(-prev, n);
if (toSignal > 0) {
this->osSignal(toSignal);
}
}
void signal(int n = 1);
private:
SkBaseSemaphore fBaseSemaphore;
};
inline void SkSemaphore::wait() {
// Since this fetches the value before the subtract, zero and below means that there are no
// resources left, so the thread needs to wait.
if (fCount.fetch_sub(1, std::memory_order_acquire) <= 0) {
this->osWait();
}
}
#endif//SkSemaphore_DEFINED

49
src/core/SkSemaphore.cpp
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@ -9,7 +9,7 @@
#if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
#include <mach/mach.h>
struct SkBaseSemaphore::OSSemaphore {
struct SkSemaphore::OSSemaphore {
semaphore_t fSemaphore;
OSSemaphore() {
@ -21,7 +21,7 @@
void wait() { semaphore_wait(fSemaphore); }
};
#elif defined(SK_BUILD_FOR_WIN32)
struct SkBaseSemaphore::OSSemaphore {
struct SkSemaphore::OSSemaphore {
HANDLE fSemaphore;
OSSemaphore() {
@ -41,7 +41,7 @@
// It's important we test for Mach before this. This code will compile but not work there.
#include <errno.h>
#include <semaphore.h>
struct SkBaseSemaphore::OSSemaphore {
struct SkSemaphore::OSSemaphore {
sem_t fSemaphore;
OSSemaphore() { sem_init(&fSemaphore, 0/*cross process?*/, 0/*initial count*/); }
@ -57,43 +57,16 @@
///////////////////////////////////////////////////////////////////////////////
void SkBaseSemaphore::signal(int n) {
SkASSERT(n >= 0);
// We only want to call the OS semaphore when our logical count crosses
// from <= 0 to >0 (when we need to wake sleeping threads).
//
// This is easiest to think about with specific examples of prev and n.
// If n == 5 and prev == -3, there are 3 threads sleeping and we signal
// SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2.
//
// If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0,
// so we don't call the OS semaphore, leaving the count at (prev + n).
int prev = sk_atomic_fetch_add(&fCount, n, sk_memory_order_release);
int toSignal = SkTMin(-prev, n);
if (toSignal > 0) {
this->osSignal(toSignal);
}
void SkSemaphore::osSignal(int n) {
fOSSemaphoreOnce([this] { fOSSemaphore = new OSSemaphore; });
fOSSemaphore->signal(n);
}
static SkBaseSemaphore::OSSemaphore* semaphore(SkBaseSemaphore* semaphore) {
return semaphore->fOSSemaphore.get([](){ return new SkBaseSemaphore::OSSemaphore(); });
void SkSemaphore::osWait() {
fOSSemaphoreOnce([this] { fOSSemaphore = new OSSemaphore; });
fOSSemaphore->wait();
}
void SkBaseSemaphore::osSignal(int n) { semaphore(this)->signal(n); }
void SkBaseSemaphore::osWait() { semaphore(this)->wait(); }
void SkBaseSemaphore::deleteSemaphore() {
delete (OSSemaphore*) fOSSemaphore;
SkSemaphore::~SkSemaphore() {
delete fOSSemaphore;
}
///////////////////////////////////////////////////////////////////////////////
SkSemaphore::SkSemaphore(){ fBaseSemaphore = {0, {0}}; }
SkSemaphore::~SkSemaphore() { fBaseSemaphore.deleteSemaphore(); }
void SkSemaphore::wait() { fBaseSemaphore.wait(); }
void SkSemaphore::signal(int n) {fBaseSemaphore.signal(n); }

9
src/lazy/SkDiscardableMemoryPool.cpp
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@ -29,7 +29,7 @@ public:
/**
* Without mutex, will be not be thread safe.
*/
DiscardableMemoryPool(size_t budget, SkBaseMutex* mutex = nullptr);
DiscardableMemoryPool(size_t budget, SkMutex* mutex = nullptr);
virtual ~DiscardableMemoryPool();
SkDiscardableMemory* create(size_t bytes) override;
@ -52,7 +52,7 @@ public:
#endif // SK_LAZY_CACHE_STATS
private:
SkBaseMutex* fMutex;
SkMutex* fMutex;
size_t fBudget;
size_t fUsed;
SkTInternalLList<PoolDiscardableMemory> fList;
@ -128,8 +128,7 @@ void PoolDiscardableMemory::unlock() {
////////////////////////////////////////////////////////////////////////////////
DiscardableMemoryPool::DiscardableMemoryPool(size_t budget,
SkBaseMutex* mutex)
DiscardableMemoryPool::DiscardableMemoryPool(size_t budget, SkMutex* mutex)
: fMutex(mutex)
, fBudget(budget)
, fUsed(0) {
@ -241,7 +240,7 @@ void DiscardableMemoryPool::dumpPool() {
} // namespace
SkDiscardableMemoryPool* SkDiscardableMemoryPool::Create(size_t size, SkBaseMutex* mutex) {
SkDiscardableMemoryPool* SkDiscardableMemoryPool::Create(size_t size, SkMutex* mutex) {
return new DiscardableMemoryPool(size, mutex);
}

3
src/lazy/SkDiscardableMemoryPool.h
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@ -52,8 +52,7 @@ public:
* the pool works.
* Without mutex, will be not be thread safe.
*/
static SkDiscardableMemoryPool* Create(
size_t size, SkBaseMutex* mutex = nullptr);
static SkDiscardableMemoryPool* Create(size_t size, SkMutex* mutex = nullptr);
};
/**