From d9f5d20f81b15190fa858eda1f536deae21e8e78 Mon Sep 17 00:00:00 2001 From: sclittle Date: Wed, 4 May 2016 18:23:30 -0700 Subject: Revert of Modernize SkMutex and SkSemaphore. (patchset #2 id:20001 of https://codereview.chromium.org/1947153002/ ) Reason for revert: This CL seems to have broken the Linux x64 and Mac bots, e.g. https://build.chromium.org/p/chromium/builders/Linux%20x64/builds/19052 https://build.chromium.org/p/chromium/builders/Mac/builds/15151 The error appears to have something to do with new static initializers being added. Original issue's description: > Modernize SkMutex and SkSemaphore. > > - use > - 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 > > Committed: https://skia.googlesource.com/skia/+/427c2819d9237d7d7729c59238036cfc73c072ea TBR=herb@google.com,mtklein@chromium.org,reed@google.com,bsalomon@google.com # Skipping CQ checks because original CL landed less than 1 days ago. NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true BUG=609340 Review-Url: https://codereview.chromium.org/1945343003 --- include/private/SkMutex.h | 56 +++++++++++++++++-------- include/private/SkSemaphore.h | 96 ++++++++++++++++++++++++------------------- 2 files changed, 93 insertions(+), 59 deletions(-) (limited to 'include/private') diff --git a/include/private/SkMutex.h b/include/private/SkMutex.h index b9af00f8a8..8c78e1205c 100644 --- a/include/private/SkMutex.h +++ b/include/private/SkMutex.h @@ -8,20 +8,33 @@ #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" -// TODO: no need for this anymore. -#define SK_DECLARE_STATIC_MUTEX(name) static SkMutex name; - -class SkMutex { -public: - constexpr SkMutex() = default; - - SkMutex(const SkMutex&) = delete; - SkMutex& operator=(const SkMutex&) = delete; - +#ifdef SK_DEBUG + #include "../private/SkThreadID.h" +#endif + +#define SK_MUTEX_SEMAPHORE_INIT {1, {0}} + +#ifdef SK_DEBUG + #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0} +#else + #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT} +#endif + +// 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();) @@ -37,9 +50,20 @@ public: SkASSERT(fOwner == SkGetThreadID()); } -private: - SkSemaphore fSemaphore{1}; - SkDEBUGCODE(SkThreadID fOwner{kIllegalThreadID};) + 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; }; template @@ -92,10 +116,10 @@ private: Lock &fLock; }; -typedef SkAutoTAcquire SkAutoMutexAcquire; +typedef SkAutoTAcquire SkAutoMutexAcquire; #define SkAutoMutexAcquire(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexAcquire) -typedef SkAutoTExclusive SkAutoMutexExclusive; +typedef SkAutoTExclusive SkAutoMutexExclusive; #define SkAutoMutexExclusive(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexExclusive) #endif//SkMutex_DEFINED diff --git a/include/private/SkSemaphore.h b/include/private/SkSemaphore.h index adee574bb7..cb2f58da4a 100644 --- a/include/private/SkSemaphore.h +++ b/include/private/SkSemaphore.h @@ -8,26 +8,43 @@ #ifndef SkSemaphore_DEFINED #define SkSemaphore_DEFINED -#include "../private/SkOnce.h" #include "SkTypes.h" -#include +#include "../private/SkAtomics.h" +#include "../private/SkOncePtr.h" -class SkSemaphore { -public: - constexpr SkSemaphore(int count = 0) - : fCount(count), fOSSemaphore(nullptr) {} +struct SkBaseSemaphore { - ~SkSemaphore(); + // 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); + } + } - // Increment the counter n times. - // Generally it's better to call signal(n) instead of signal() n times. - void signal(int n = 1); + // Increment the counter N times. + // Generally it's better to call signal(N) instead of signal() N times. + void signal(int N); // Decrement the counter by 1, // then if the counter is <= 0, sleep this thread until the counter is > 0. - void wait(); + 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(); -private: // This implementation follows the general strategy of // 'A Lightweight Semaphore with Partial Spinning' // found here @@ -37,40 +54,33 @@ private: // 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. - struct OSSemaphore; - - void osSignal(int n); - void osWait(); - - std::atomic fCount; - SkOnce fOSSemaphoreOnce; - OSSemaphore* fOSSemaphore; + int fCount; + SkBaseOncePtr fOSSemaphore; }; -inline void SkSemaphore::signal(int n) { - int prev = fCount.fetch_add(n, std::memory_order_release); +/** + * 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(); - // 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 wait(); -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(); - } -} + void signal(int n = 1); + +private: + SkBaseSemaphore fBaseSemaphore; +}; #endif//SkSemaphore_DEFINED -- cgit v1.2.3